Brake Handbook 0895862328, 9780895862327

Citation preview

choose, install, test & service brakes. Disc- & drum-brake sign. Brake materials for racing or street. Air cooling & water ceding. Proportioning valves & balance bar Practical da'ta & formulas.

Fred Puhn

HPBooks@

11ArlDBOOK Fred Puhn Registered Professional Fred Puhn Engineer Registered Professional Engineer

I

3

3 4 Corvette rotor-ano-caliper assembly by Girlock, modified·for racing by Tilton Engineering. Neal Products brake-pedal , balance-bar, bracket & dual master-cylinder assembly ; Airheart master Corvette rotor-and-caliper for racing Engineering. cylinders shown. ·' . _ _assembly _ . . by - Girlock, 'modifled . - by Tilton -Neal Products brake-pedal, balance-bar, & dual master-cylinder assembly; Airheart master Tempilaq temperature-sensing paintfrornbracket Big"Three Industries; cylinders shown. Alston proportioning valve. .... 3. Tempilaq temperature-sensing paint from Big-Three Industries. 4. Alston proportioning valve. 1. 2. 1. 2. 3. 4.

Contents 11 2 3 3 4 5 6 6 7 7 8 8 9 9 10 10 11 11 11 22

Introduction ............................................ 33 Introduction ............................................ Basics................................................. Basics ................................................. 44 Drum Drum Brakes Brakes .......................................... .......................................... 1155 ........................................... 23 Disc Disc Brakes Brakes ........................................... 23 Friction Friction Material Material ....................................... ....................................... 34 34 Hydraulic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 42 Hydraulic Systems Systems .... ..................................... 42 Brake Brake Pedals Pedals & & Linkages Linkages ............................... ............................... 66 66 Power Assist .......................................... .......................................... 77 77 Other Types Types of Brakes Brakes ................................. ................................. 82 82 HighPerformance Brakes High-Performance Brakes .............................. .............................. 88 88 Testing Testing ............................................. ............................................. 104 104 ........................................ 1121 Maintenance Maintenance ........................................ 21 Modifications........................................ Modifications ........................................ 1 37 37 Trouble-Shooting Guide .............................. .............................. 166 1 66 Suppliers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 Suppliers List. List ........................................ 169 69 Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 71 Reference Tables ..................................... 71 Index ............................................... 174 174

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THANKS Thanks to the many brake brake suppliers and and experts experts who helped helped with technical information and Tilton Engineering, Bill Bill Neal Neal of Neal Neal and photographs. photographs. Special Special thanks to Mac Tilton of Tilton Products, and John Moore of AP Racing Racing for their personal contributions. Products, cohtributions. Thanks also to Carroll Smith Carroll Smith of Carroll Carroll Smith Consulting for helpful helpful suggestions given given after reading reading the finished manuscript. Special thanks to Garrett Van Camp, Camp, Van Camp Racing Racing Enterprises, Inc., 25192 Maplebrooke, Southfield, MI MI 48034. His His heroic efforts and and great technical knowledge gained Ford Motor brake-design engineer and and race-car brake-design gained over the years as a Ford made a significant contribution to the content and completeness of this book. consultant made book. It could been this quality without him. Thanks Garrett. could not have been

NOTICE: in this book is true and complete to the best of our knowledge. All NOTICE: The information contained in guarantees on the part of the author or recommendations on parts and procedures procedures are made without any guaranteeson the quality of parts, materials and methods are beyond control, author and HPBooks. Because thequality beyond our control, publisher disclaim all liability incurred in connection with the use of this information. information. SAE.; Senior Publisher: Rick Bailey; Editor: Randy Summerlin; Editorial Editorial Director: Monroe, P.E., Publisher: Bailey; Executive Editor: Director: Tom Monroe, P.E., S.A.E.; Editor: Don Burton; Editor: Ron Ron Sessions, Sessions, A.S.A.E.; A.S.A.E.; Art Director: Director: Don Burton; Book Design: Design: Paul Fitzgerald; Fitzgerald; Production Production Coordinator: Coordinator: B. Narducci; Coatsworth; Typography: Typography: Michelle Michelle Carter; Carter; Director of Manufacturing: Manufacturing: Anthony B. Narducci; Photos: Photos: Fred Fred Cindy J. Coatsworth; Puhn, Bill Keller Puhn, others noted; noted; Cover Photo: Photo: Bill

Published by HPBooks A Division of HPBooks, Inc. P.O. 50 P.O. Box 5367, 5367, Tucson, A2 AZ 85703 6021888-21 602/888-2150 0-89586-232-8 Library of Congress Catalog Number 84-62610 84-62610 ISBN 0-89586-232-8 Inc. Printed in U.S.A. U.S.A. ©1985 HPBooks, HPBooks, Inc. 01985 2nd Printing Printing 2

Introduction

When driving down a long hill on a crowded freeway, a situation can occur that demands good brakes. Many of the cars in this photo are going over 55 mph . If an emergency were to happen, the resulting chain-reaction braking would result in some drivers locking the wheels.

When driving down a long hill on a crowded freeway, a situation can occur that demands good brakes. Many of the cars in this photo are Most of55usmph. onlyIf an think about were brakes problems, too. chain-reaction braking would result in some drivers locking the wheels. going over emergency to happen, the resulting

when a panic stop occurs ahead in trafof we us only think about brakes ficMost and all see are brakelights and when a panic stop occurs ahead trafthe undersides of cars. Theseinnearfic and all weillustrate see are brakelights and emergencies how important the undersides of safety. cars. These brakes are to our Brakesnearare emergencies illustrate important, also a vital part of highhow performance brakes are can to our safety. Brakes are as any racer tell you . also a vital part of high performance, Because everyone wants higher peras any racerand cansafety, tell you. formance brakes deserve a Because wants pergreat deal everyone of attention. Wehigher not only formance and safety, brakes deserve want our car to go fast , but it shoulda great dealquickly of attention. We not also stop and safely. Anyonly car want powerful our car toand go fast, but it should with consistent brakes also stopconfidence quickly andin safely. Any car instills the driver. It with powerful and consistent brakes also increases driving pleasure. Bad instills confidence brakes are terrifying. in the driver. It also increases driving If racing is your game,pleasure. you needBad to brakes are terrifying. know more about brakes than the If racing is your game, what you need to casual driver. No matter type of know more about brakes than the racing you do, brake performance is casual driver.racing NO matter type of vital. Road is mostwhat demanding racing you do, brake drag performance is on brakes, although racing and vital. Road racing is most demanding oval-track events have special

on brakes, although drag racing and oval-track events have special

I talk about brakes as a system. This

problems, too. lines, pedals, levers includes fluid, I talk about a system. This and linkages, brakes as wellas as the brake includes fluid, lines, pedals, levers units. Wheels, bodywork and even and linkages, as well as the brake the frame structure become a part of units. Wheels, bodywork and affect even the brake system when they the frame structure This become a part of brake performance. book covers the brake system when they affect each part of the system and how it rebraketoperformance. book covers lates overall brakeThis performance. It each help part of andofhow it rewill in the the system selection compolates braketo performance. It nents toif overall you prefer design a brake will help in the selection of composystem. nents yousection prefer of to the design a brake The iffirst book deals system.particular parts of a brake with The first the book deals system. Thesection secondofsection, starting with particular parts of a brake with Chapter 9, describes how to system. second starting design , The install, test,section, maintain and with 9, system describesfor how to modifyChapter a brake racing design, install, test, maintain and applications. Race-car concepts also modify toa brake system for racing apply high-performance road concepts applications. vehiCles. I alsoace-bar note where there also are apply to differences high-performance road important between racing vehicles. I also note where t'here are and road use . important differences between racing and road use.

Braking is essential in winning races. These stock cars are competing on a road course-the severe for automoBraking is most essential in duty winning races. tive brakes. cars Notice thea right aresmoke from On road front tire on most car that's braking hard in the course-the severe duty for automocorner. tive brakes. Notice smoke from the right

front tire on car that's braking hard in the corner.

3

Basics

I

Good brakes are essential to overall vehicle performance. Even though engine performance, suspension and body aerodynamics approach perfection, race cars, such as this GTP Corvette, will not be competitive without good brakes. Photo by Tom Monroe.

Good brakes are essential to overall vehicle performance. Even though engine performance, suspension and body aerodynamics approach perfection, race cars, such as this GTP Corvette, will not be competitive goodtobrakes. by Tomthe Monroe. systems are without designed do Photo Brake brakes, friction materials rub

Most production sedans have drum brakes on the rear and disc brakes on the front. Drum brakes are sedans preferred on drum rear wheels Most ~roduction have brakes because a parking brake is easily adapted on the rear and disc brakes on the front,. This drum on the rear of awheels 2-ton Drumlarge brakes are ispreferred on rear sedan. a parking brake is easily adapted. because ~

-

- -

This large drum is on the rear of a 2-ton sedan.

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one thing-stop the vehicle. Sounds Brake designed to do easy, but systems problemsare start when brakes one the from vehicle. mustthing-stop stop a vehicle highSounds speed easy, but problems startdowhen brakes in a short distance, and it over and must stop a vehicle from high speed over again . We expect no failures or in distance,All andbrake do it over and lossa short of control. systems over again. expectThe no failures or should stop We a vehicle. difference loss of control. All brake systems between a good system and a bad one should stop ita vehicle. The difference is how well will perform under the between a good system and a bad one most adverse conditions. is All howvehicles well it will the haveperform brakes, under and they most adverse conditions. always did . Ever since m an discovered vehicles have itbrakes, and they theAll wheel , stopping was a problem. always did. Ever since discovered Carts, wagons and man carriages had the wheel, stopping it was a problem. brakes, usually simple blocks rubbing Carts, wagons carriagesa basic had on a wheel. This and established brakes, usually simple blocks rubbing that has yet to change, even with the on a wheel. This established a basic most sophisticated brake system: All that hasuse yetfriction to change, with the brakes to stopeven the vehicle.

most sophisticated brake system: All brakes usefiiction BRAKE TYPES to stop the vehicle.

When two parts rub together, the

BRAKE resulting TYPES friction generates heat. In When two parts rub together, the resulting friction generates heat. In

against metal surfaces . Different types brakes, friction materials of brakes the are arranged differently,rub or against metal surfaces. Different use different methods of forcing types rubof brakes are together. arranged There differently, or are also bing surfaces use different methods of forcing rubdifferences in dissipating heat once it bing surfaces together. There are also is generated. differences in dissipating heat once or it Either drum brakes or disc brakes, generated. of the two, are used on ais combination Either drum brakes disc brakes, most vehicles. Theseorterms refer or to ahow combination of the two, are usedand on friction surfaces are designed most vehicles. These terms refer to configured. how friction surfaces are and Drum Brakes-All eadesigned rly vehicles configured. used drum bra kes ; many of today's Drum early vehicles vehicles Brakes-All still do . The rubbing surface used drum brakes;called many of today's drum , is a metal cylinder a brake vehiclesmade still do. Theiron rubbing surface usually of cast . is aEarly metal drum cylinderbrakes called awere brake drum, exterusually made ofsurface cast iron. nal-rubbing was outside of brakes internal were extertheEarly drum.drum More modern drum nal-rubbing surface was outside of brakes have the rubbing surface inside the drum. More modern internal drum the drum. There are shoes inside the brakes with have frict the ion rubbing surface inside. drum material attached the drum. are isshoes inside This frictionThere material called lining.the It

drum with friction material attached. This friction material is called lining. It

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Honda disc brake is typical of front brakes on small sedans. Exposed rubbing I surface of disc brake aids cooling. Honda disc brake is typical of front brakes

Iused

used on small sedans. Exposed rubbing surface of disc brake aids cooling.

is designed to rub against the drum without burning, melting or wearing is designed rub are against theagainst drum The to shoes forced rapidly. without burning, melting or wearing the inside surface of the drum when rapidly. Thepushes shoes are the driver the forced brake against pedal, the insidefriction surfacebetween of the drum when the lining creating the driver pushes the brake pedal, and the drum surface . Drum brakes creating friction between in Chapter 2. the lining are covered and the drum surface. Drum brakes Disc Brakes - A modern brake are covered in Chapter 2. design is the disc brake. The drum is Disc modern replacedBrakes-A by a flat metal disc, or brake roto;; design is the disc brake. The drum is with a rubbing surface on each side. replaced by a flat metal disc, or rotot; The rotor is usually made of cast iron. with a rubbing surface on each side. Friction materials are inside a caliper, The rotor is usually made of cast iron. which surrounds the rotor. Disc-brake Friction materials are inside caliper, friction material-one on eacha side of which surrounds the rotor. Disc-brake the rotor- is called a brake pad, puck friction each side of or lining.material-one This caliper on is designed to the rotor-is a brake pad,ofpuck clamp the padscalled against the sides the or lining. This caliper designed to rotor to create friction.is Disc brakes clamp the pads against 3. the sides of the are covered in Chapter

Earliest automotive brakes were drum type with the rubbing surface on the outside of the drum. Because brakes frictionwere material surEarliest automotive drum type rounds outside of theon drum, coolwith thethe rubbing surface the little outside of ing air contacts the friction hot rubbing surface. the drum. Because material surExternalthe drum brakes are drum, simplelittle and cooleasy rounds outside of the to but have coolingsurface. ability. ingservice, air contacts thehorrible hot rubbing

External drum brakes are simple and easy to service, but have horrible cooling ability.

Finned aluminum drums give better cooling than plain cast iron. Caliper P = Clamping Force on Rotor

p

P

=

Clamping Force on Rotor

Caliper Mounting Bolt -

-

- Axle Centerline

Axle Centerline

rotor to create friction. Disc brakes are covered in Chapter 3.SYSTEM BRAKE-ACTUATING

Wheel Stud

Between the driver's foot and the BRAKE-ACTUATING SYSTEMthat wheel brakes are components Betweenforce the from driver'sthefoot and into the translate driver wheel brakes are components that friction force at the brake-rubbing translate force into surfaces. I callfrom this the thedriver actuating friction force at the brake-rubbing system. This system can be mechanisurfaces. I call this theor aactuating cal, hydraulic , pneumatic combisystem. This system canvehicles be mechanination of these . Future could cal, pneumatic or a combiWhatever the use hydraulic, electric systems. nation these. Future vehicles could type ofof actuating system, the result is use electricWhen systems. Whatever the the same: the driver operates typesystem, of actuating the .result is the brakessystem, are applied the same: When the driver operates Brake Pedal & Linkage-Brake the system, brakes areare applied. pedals and linkages integral parts Brake Pedal & Linkage-Brake

Stud

pedals and linkages are integral parts

Prewar MG used mechanical brakes. Front brakes are operated by cables that flex as the wheels steer mechanical and move up and down. Prewar MG used brakes. Front Finned aluminum drums better brakes are operated by give cables that cooling flex as thanwheels plain cast iron.and move up and down. the steer

ｾｒｯｴｲ＠

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Rotor Disc brake operates by clamping rotor between two stationary pads. Rotor turns with the wheel; caliper is mounted to a fixed part of the suspension, usually the spindle or upright. I I

Disc brake operates by clamping rotor between two stationary pads. Rotor turns with the wheel; caliper is mounted t o a fixed part of the suspension, usually the spindle or upright.

of a brake system. The pedal is the familiar lever that the driver pushes of a brake system. pedal the fawith his foot to The apply the is brakes. miliar lever that the driver pushes Regardless of the type of brakewith his system foot toused, apply the applicabrakes. actuating system Regardless the with type the of braketion always ofbegins driver actuating used, system operating system a pedal-or lever applicain rare tion always beginsdesign with determines the driver cases. Brake-pedal operating a pedal-or in rare the leg force required tolever stop the car.

cases. Brake-pedal design determines the leg force required to stop the car.

It is also a factor in determining how solid the brakes feel to the driver. It Trade-offs is also a factor in determining how when designing are made solid brakesLong feel to the driver. brakethe pedals. pedals reduce the Trade-offs are madetowhen pedal force required stop adesigning vehicle. brake pedals. Longpedals pedals have reducelong the However, long pedal force required to stop a vehicle. travel. They can also feel spongy to the However, long pedals long driver. Brake-pedal design have is detailed travel. They6. can also feel spongy to the in Chapter

driver. Brake-pedal design is detailed in Chapter 6 .

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Although most mechanically actuated brakes are found on antique cars, some are still being used. by APactuated Racing Although most Developed mechanically for useare onfound competition brakes on antiquerally cars,cars, somethis are modern caliper mechanically actuated. still being used. isDeveloped by AP Racing Independent the hydraulically actuated for use on of competition rally cars, this brakes, calipers are used onactuated. the rear modern these caliper is mechanically for high-speed on slick surfaces. Independent of control the hydraulically actuated Photo courtesy AP Racing. brakes, these calipers are used on the rear

for high-speed control on slick surfaces. Photo courtesy AP Racing.

Early race cars had no front brakes. Although this Peugeot was a winner with its advanced high-speed dual-overhead-cam engine, it used cable-operated rear-wheel brakes.

Early race cars had no front brakes. Although this Peugeot was a winner with its advanced high-speed dual-overhead-cam engine, it used cable-operated rear-wheel brakes.

In the '20s, Duesenberg introduced hydraulic brakes with large finned drums . This was probably the firstintroduced road car with In the '209, Duesenberg hyenough horsepower required great draulic brakes with that large finned adrums. improvement in braking. It didroad not car use with flex This was probably the first hoses, but instead ranthat fluidrequired through internal enough horsepower a great passages in the improvement in suspension. braking. I t did not use flex

hoses, but instead ran fluid through internal passages in the suspension.

The brake pedal is connected to a linkage that transfers force to the acThe brake pedal connected to asa tuating system. Thisislinkage can be linkage asthat transfers force to the ac-a simple a push/pull rod operating tuating hydraulic system. This linkage can beOr, as single master cylinder. simple as a push/pull rod operating the linkage may be a complicated, ad-a single master cylinder. Or, justablehydraulic balance-bar system for changthe linkage maybetween be a complicated, ading the balance front and rear justable balance-bar system for changbrakes. Early-design, mechanicaling the balance between front actuating linkage extends all and the rear way brakes. Early-design, mechanicalto the brakes themselves. Brakeactuating linkageis extends all inthemore way linkage design discussed to the brakes themselves. Brakedetail in Chapter 6. linkage designBrakes-The is discussed in more Mechanical simplest detail in Chapter 6. brake-actuating system is a mechaniMechanical Brakes-The simplest cal system. The brake pedal operates brake-actuating system is a mechanicables or rods that apply the brakes cal system. The isbrake pedal operates when the pedal pushed . Early sys-

cables or rods that apply the brakes when the pedal is pushed. Early sys-

6

tems were mechanical and are still used for parking brakes on presenttemsvehicles. were mechanical and are still day The mechanical linkage used fortheparking brakes onin presentmoves shoes outward a drum day vehicles. The mechanical linkagea brake, or clamps the pads against moves the shoes outward in a drum disc-brake rotor. brake, or clamps the pads against Hydraulic Brakes-Modern cars usea disc-brake rotor. In a hydraulically achydraulic brakes. Hydraulic Brakes-Modern tuated system, the cables or cars rodsuse of hydraulic brakes. In a hydraulically the mechanical system are replaced acby tuated system, or rods of fluid-filled lines the and cables hoses. The brake'the mechanical system are replacedinbya pedal linkage operates a piston fluid-filled linestoand hoses. The master cylinder pressurize thebrake: fluid pedal linkage operates a piston in a inside the lines and hoses. Fluid presmaster cylinder to pressurize the fluid sure in each wheel cylinder forces the inside the lines and hoses.the Fluid presfriction material against drum or sure eachChapter wheel cylinder the rotor.inSee 5 for aforces detailed friction material against the drum or explanation of how a hydraulic system rotor. See Chapter 5 for a detailed works. explanation of how a hydraulic system, Pneumatic Brakes-In a pneumatic works. or air-brake, system the brakes are Pneumatic by Brakes-In a pneumatic, controlled compressed air. Air or air-brake, system the are brakes are generally usedbrakes on large controlled compressed air. Air commercial by vehicles and trucks. An brakes are of generally used on brake large advantage the pneumatic commercial vehicles and trucks. An system is safety. Small leaks cannot advantage of the pneumatic brake cause a total loss of braking because system is safety. supplied Small leaks air is constantly by acannot comcause total stored loss ofinbraking because pressora and large volume. air is constantly suppliedoperation by a comPneumatic brake-system is pressor and stored in large described briefly in Chapter 8. volume.

Pneumatic brake-system operation is described briefly in Chapter 8. BRAKE HISTORY

The earliest brakes were derived BRAKE HISTORY from those used on horse-drawn The earliest derived wagons. As carsbrakes becamewere heavier and from those used on horse-drawn more powerful, these primitive

wagons. As cars became heavier and more powerful, these primitive

brakes soon were improved to the early external- type drum brakes, all brakes soon were improved to the mechanical-actuating systems. with early external-type drum all Early brakes were on brakes, the rear with mechanical-actuating systems. wheels only. The major reason for this Early brakes were on thean rear was the difficulty in designing acwheels only. The major reason for this tuating system on wheels that are was the difficulty designing acsteered. Engineersinavoided the an probtuating system on wheels that are. lem by omitting front-wheel brakes steered. the probAnother Engineers reason foravoided not using front lem by omitting front-wheel brakes was concern that the carbrakes. might Another reason for not usingbrakes front tip over on its nose if front brakesapplied was concern were hard! that the car might tipEarly over external-type on its nose if drum front brakes brakes were applied hard! used a band of friction material outEarly external-type brakes side the drum. This typedrum of brake was used to a band of but friction materialmateouteasy design, the friction side the drum. thehisdrum typefrom of brake was rial prevented cooling. easy to design, but the friction mateAlso, exposed friction materials were rial prevented the drum su bject to dirt, oil from and cooling. water Also, exposed friction materials were contamination. When the brake shoes subject to dirt, oil and water were relocated inside the drum, a contamination. Whenwas the born. brake These shoes modern drum brake were relocated theRenault. drum, a were first used oninside the 1902 modern drumfour-wheel brake was braking born. These Although was were first used on the 1902 Renault. tried early in the 20th century, most Although was early cars hadfour-wheel rear brakes braking only. Then, triedtheearly in the 20thdiscovered century, most in 1920s it was that early hadadded rear brakes front cars brakes greatlyonly. to aThen, car's in the 1920s it was discovered that stopping a bility, and they were judged front brakes added greatly to a car's safe. Four-wheel brake systems soon stopping ability, and they were judged became universal. safe. Four-wheel brake systems systems soon were Mechanicalac tuating became universal. still used on most cars until the late Mechanical-actuating systems came were '20s when hydraulic systems still most cars until late into used use . onMechanical brakesthewere '20s when hydraulic systems came used for auto rac ing long after hydrau-

into use. Mechanical brakes were used for auto racing long after hydrau-

Internal details of early Duesenberg hydraulic drum brake: Notice fluid passages through axle, kingpin and spindle. Sealing was a problem solved by use of flexible hydraulic lines. I

Ieventually

Internal details of early Duesenberg hydraulic drum brake: Notice fluid passages through axle, kingpin and spindle. Sealing was a problem eventually solved by use of flexible hydraulic lines.

.

This little disc brake started it all-first disc brake used on a mass-produced car. Goodyeardiscstarted brakesit were ofThis little Hawley disc brake all-first fered on Crosley Hotshot and Supersports disc brake used on a mass-produced car. roadsters in the early '50s. A were Crosley Goodyear-Hawley disc brakes ofHotshot won theHotshot first Sebring 12-hour fered on Crosley and Supersports endurance in race with these brakes. In later roadsters the early '50s. A Crosley years, they were for small 12-hour sportsHotshot won thepopular first Sebring racing cars.race with these brakes. In later endurance

years, they were popular for small sportsracing cars. were developed for passensystems lic ger cars. The simple mechanical brake lic systems developed system waswere reliable, easy for to passenunderger cars. The simple mechanical brake stand and maintain, and not subject to system was easy that to undersudden loss reliable, of braking could stand not subject happenandto maintain, a hydrau and lic system with toa sudden loss of braking that could failed line or seal. happen to a hydraulic system with After World War II, disc brakesa failed or seal. The first production began line to appear. War 11,wasdisc carAfter with World disc brakes thebrakes 1949 began to appear. The first production Crosley Supersport. Disc brakes were car disc brakes on was the the 1949 usedwithsuccessfully 24Crosley Supersport. Disc brakes hours-of-LeMans-winning Jaguarwere in

used successfully on the 24hours-of-LeMans-winning Jaguar in

Since the mid-'50s, disc brakes have been highly developed for both racing and road use. Companies such as JFZ Engineered Products have taken brake development far beyond the early concept. Rotors, brake-mounting haveand all benefited Since thedisc-brake mid-'50s, disc brakes havepads beenand highly developed forhardware both racing road use. from rigors of faster Photo courtesy Engineered Products. JFZ cars. Engineered Products.IFZ have taken brake development far beyond Companies such as race

the early disc-brake concept. Rotors, pads and brake-mounting hardware have all benefited from fasterbrakes race cars. Photo courtesy JFZ Engineered the rigors '50s. ofDisc soon became design, there Products. have been many impor-

popular on many race cars. Indianathe '50s. Disc used brakes became polis 500 cars discsoon brakes early popular on many race cars. Indianatoo, but they had little effect on the polis 500 of carsraces usedondisc early outcome thisbrakes fast track. too, but had little effect the at they LeMans, where carsonmust Only outcome of races on this fast track. decelerate from 180 to 30 mph every Only at do LeMans, lap, and it for 24where hours,cars weremust disc to limit. 30 mph every decelerate fromto 180 brakes tested their Even in lap, anddrum do it brakes for 24 hours, racing, are stillwere useddisc in brakes classes, tested tobut their Evenrace in certain mostlimit. modern racing, brakes are still used in cars use drum disc brakes. certain classes, but most modern race the basic changes in brake Beyond

cars use disc brakes. Beyond the basic changes in brake

tant improvements. Brake systems

design, there havesafe; beenand many importoday are very complete tant improvements. Brake systems system failure occurs rarely. Modern today are brakes can very go forsafe; yearsand withcomplete little or system failure in occurs rarely.use Modern no attention highway , but brakes years with or therein can lies go a for problem: Whenlittle really no attention in highway use, but needed , performance may be marginal therein a problem: When because lies of inattention . This bookreally will needed, may be marginal help you performance keep that from happening. because of inattention. This book will help you keep& that from happening. FRICTION ENERGY Friction is resistance to sliding . Any FRICTION & ENERGY Friction is resistance to sliding. Any 7

Type of Energy

..

Friction Force Friction Friction between the box and floor is what Force makes the box difficult to slide. If box weight frictionthe between floor and Friction or between box andthe floor is what box increases, sodifficult must theto force to slide it. makes the box slide. If box Heat is or developed on slidingthe surfaces as weight friction between floor and box is moved. so must the force to slide it. increases, Heat is developed on sliding surfaces as two isobjects box moved. in contact with and trying

to move relative to each other have two objects in contact and trying friction. It can be high with or low dependto move each other have ing on therelative types ofto surfaces in contact. friction. It can be high or low dependFriction helps keep your feet from ing o n the in contact. sliding outtypes fromof surfaces under you. When Friction helps keep your feet isfrom you are standing on ice, friction low sliding fromto prevent under you. When and it is out difficult slipping. you standing on ice, If are two surfaces in friction contactis low are and it is difficult to prevent sliding, the friction createsslipping. heat. You two surfaces contact your are canIf confirm this byin rubbing

sliding, the friction creates heat. You can confirm this by rubbing your KINETIC ENERGY OF ROTATION

KINETIC ENERGYan object with Strictly speaking, OF ROTATION kinetic energy can be either moving Strictly speaking, an object with in a straight line or rotating about its kinetic energyofcan be either own center gravity (CG).moving In a in a straightcar, line or rotating about its speeding kinetic energy is own gravity a mostlycenter in the of moving car. (CG). UnlessInthe speeding car, down kinetic is car is spinning the energy road, less mostly in the moving Unless the than 10% of the total car. kinetic energy car is spinning downparts the of road, is stored in rotating the less car. than 10%parts of theinclude total kinetic energy Rotating tires, wheels, is storedengine in rotating parts line. of the brakes, and drive ａ､ｩｾ＠ car. Rotating partsenergy include tires, in wheels, tional kinetic stored these brakes, engine and drive line. Addirotating parts must be absorbed in tional kinetic energy stored these the brakes. However, to makeincalcurotating simpler, parts must be absorbed in lations I ignore the small the brakes. However, to make calcuamount of kinetic energy stored in lations simpler, I ignore the small rotating parts. amount of kinetic in At high speed, energy kineticstored energy rotatinginparts. stored the rotating tire-and-wheel At high speed, kinetic energy assemblies increases significantly. stored If you in hitthe therotating brakestire-and-wheel hard at high assemblies increases significantly. speed, the rotating parts must be If you hitbefore the brakes hardcan at high stopped the wheel lock speed, the Itrotating partsand must be and slide. takes time pedal stopped the rotating wheel can lock effort to before stop this weight, and slide. takes time slow and at pedal even if the Itcar doesn't all. effort to stop this rotating weight, Consequently, it is more difficult to even if the car doesn't slow at all. lock the wheels when traveling at Consequently, it is Ironically, more difficultthis to higher speeds. lock the wheels traveling makes a car saferwhen at high speed at if higher speeds. the driver panics Ironically, and hits this the makes a safer at highinspeed brakes toocar hard. However, racing,if the driver panics it increases pedal and effort hits as the brakestries too hard. However, in racing, driver to reach the traction limit it the increases pedal effort as the of tires. driver tries to reach the traction limit of the tires. 8

Example

Heat Energy stored ina hot brake rotor. Type of Energy Example Sound Noise from exhaust. Heat Energy stored in a hot brake rotor. Ught Light from headlights. Sound Noise exhaust. Stored Mechanical Energyfrom stored in a compressed coil spring. Light Light from headlights. Energy in agallon of gasoline. Chemical Stored Mechanical Energy stored a compressed spring. Electrical Current from a in battery turning a coil starter. Chemical Energy in a energy gallon of Radiation Microwave in gasoline. a microwave oven. Electrical Current from a ina battery turning a starter. Kinetic Energy stored speeding bullet. Radiation Microwave energy in a microwave oven. Kinetic Energy stored initacan't speeding bullet. Energy can be changed from one form to another, but be created or destroyed. Here are some different forms of energy. Most forms are transformed into heat after energy does itscan useful work. Energy be changed from one form to another, but it can't be created or destroyed. Here are some different forms of energy. Most forms are transformed into heat after energy does useful work. handsitstogether rapidly back and forth. varies as the square of speed. To calcu-

You can feel the warmth. This friction hands together back and can help warm rapidly your hands on aforth. cold You can feel the warmth. This friction day. In brakes, friction is used to can help warm handsofo ncreating a cold create heat. Theyour process day. In brakes, heat stops the car. friction is used to create heat. T h eofprocess creating The amount frictionof between heat stops the car. two rubbing surfaces depends on the T h e amount of friction between materials and their roughness. The two rubbing surfacesis depends amount of friction describedo nbythea materials called and their e number the roughness. coefficient T hof amount of friction is described by a friction. A high number means a large number ofcalled the a coefficient of amount friction; low number A high number means a large .friction. means a small amount of friction. amount of about friction; a low Read more friction at thenumber beginmeans a small amount of friction. ning of Chapter 4. Read moreisabout frictionto atdothe beginEnergy the ability work. A ning of Chapter 4. moving car develops energy. The Energy is the ability to doenergy work. A faster it moves, the more it moving car energy. The develops. Thisdevelops type of energy is called faster moves, thespeed moreis energy kinetic it energy. When doubled,it develops. This type of energy is called four times the kinetic energy is kinetic energy. W h e n speed is doubled, developed. That is, kinetic energy

four times the kinetic energy is developed. That is, kinetic energy TEMPERATURE & HEAT

The difference between temperature TEMPERATURE & HEAT We all and heat may be confusing. The familiar difference between temperature are with temperature, meaand heat confusing. We all sured in may eitherbedegrees Farenheit are familiar with temperature, (F) or degrees centigrade (Cl. measured Farenheit Heat inis either a formdegrees of energy. When (F) or isdegrees (C).itstemheat added centigrade to a material, Heat is arises; form of energy. When perature when heat is heat is added a material, its temremoved, its totemperature drops. perature rises; when heat of is Thus, temperature is the effect removed, its temperature drops. adding or subtracting heat energy. Thus, ,Itemperature is the effect When say something heats up, ofI addingheat or subtracting mean is added. heat Whenenergy. I say When I say something heats up, InI cools off, I mean heat is removed. mean case, heat is When of I say either theadded. temperature the cools off, I mean heat is removed. In object changes. either case, the temperature the I measure kinetic energy inoffootobject changes. pounds (It-I b). However, it could be I measure footmeasured in kinetic British energy ThermalinUnits pounds it could be (BTU's), (ft-lb). just asHowever, engineers do .. One measured British Units BTU is the in amount of Thermal heat it takes to (BTU's), as engineers One raise the just temperature of onedo. pound BTU IS theby amount of heat Farenheit. it takes to of water one degree raise BTU the temperature oneIt-Ib pound One is equal to of778 of of waterorbyone oneft-Ib degree Farenheit. energy, equals 0.0013 One is equal to 778 offt-lb of BTU. BTU Although one pound water energy, or one ft-lb equals 0.0013 BTU. Although one pound of water

late kinetic energy of a car, use the folvaries as the square of speed. To calculowing formula:

late kinetic energy ofS2a car, use the folWc lowing Kinetic formula: energy = - -

29.9 W,S2 = Kinetic energy in foot-pounds (It-Ib) 29.9 W = Weight of Car in pounds (Ib) in c= foot-pounds S Speed of(ft-lb) car in miles per hour = Weight of Car in pounds (Ib) W, (mph) S = Speed of car in miles per hour Converting Energy-The first law of (mph)

thermodynamics says: Energy can Converting law of never be Energy-The created nor first destroyed. thermodynamics can However, energy says: can beEnergy converted neveronebeform created nor destroyed. from to another. However, canenergy be converted Differentenergy forms of are heat, from o n e form to another. sound, light, stored mechanical, Different electrical forms of energy heat, chemical, and are radiated. sound, electrical light, stored mechanical, Stored energy in a battery chemical, will convert electrical energy intoand heatradiated. or light Stored electrical energy by connecting the batteryin toa battery a light will into heat or light bulb.convert Stored energy mechanical energy in a by connecting battery to to kinetic a light spring can be the converted

bulb. Stored mechanical energy in a spring can be converted to kinetic changes temperature one degree F when one BTU of heat is added, F changes temperature one react degree other materials do not the when of heat change is added, sallle. one TheirBTU temperature is other materials do BTU not of react different when one heatthe is same. Their temperature change is added. different when one BTU of heat is The relationship between temadded. perature change and heat-energy The relationship temchange is governed between by a property perature change andEach heat-energy ca ll1ed specific heat. material change is governed by aasproperty has its own specific heat shown called specific heat. in Each for typical materials the material accomhas its own specific heatheat as shown panying table. Specific is the for typical materials thepound accomtemperature rise for in one of panying table. is the material when Specific one BTU heat of heat is temperature rise forspecific one pound added. A material's heat of is material when one of heat is very important to aBTU brake-design added. A material's spec~ficheat is engineer for calculating brakevery important to a temperature change for brake-design each stop. engineer for calculating Ideally, brakes should be brakemade temperature change eachspecific stop. from materials with for a high Ideally, should inbea made heat. This brakes would result small from materials high specific temperature r isewith for aa given amount heat.kinetic This would a small of energyresult put ininto the temperature rise for a given amount brakes. A small temperatur e rise of kinetic energywouput intofewer the means the brakes l1d have brakes. A small temperature rise problems. means the brakes would have fewer problems.

MELTING TEMPERATURE Material

Degrees F Degrees C MELTING TE'MPERATURE

Water Material Beryllium - pure Water Beryllium-QMV Beryllium-pure Magnesium-AZ 31 B-H24 Beryllium-QMV Aluminum-6061- T6 Magnesium-AZ 31 6-H24 Aluminum -2024-T3 Aluminum-6061 -T6 Carbon-pure Aluminum-2024-T3 Titanium-pure Carbonpure120VCA Titanium-B Titanium-pure Magnesium-HK 31 A-H24 Titanium-B 120VCA Stainless Steel-304 Magnesium-HK 31A-H24 Cast Iron Stainless Steel-304 Steel-C1020 Cast Iron Copper-pure

Degrees F

32 2340 32 2340 2340 1100 2340 1080 1100 940 1080 6700 940 3070 6700 3100 3070 1100 31 00 2600 1100 2750 2600 2750 2750 1980

Steel-C1020

0 1282 0 1282 1282 593 1282 582 593 504 582 3704 504 1688 3704 1704 1688 593 1704 1427 593 1510 1427 1510 151 0 1082

2750

1510

Degrees C

SPECIFIC HEAT SPECIFIC BTU/1 b/F

HEAT 1.00 BTU/l b/F

0.52 1.oo 045 0.52 0.25 0.45 0 .23 0.25 0.23 0.23 0 .16 0.23 0.14 0.1 6 0 .13 0.1 4 0 .13 0.1 3 0 .12 0.1 3 0.10 0.1 2 0.10 0.10 0 .09

0.10

Specific heats of various materials are1980 listed from the highest heat is Copper-pure 1082 to lowest. Specific 0.09 amount of heat energy required to raise one pound of material by one degree Fahrenheit . Material heats with highest specific heat are is not necessarily besttoforlowest. brakes. To be a good Specific of various materials listed from the the highest Specific heat is brake material, must withstand temperature, conduct heat and have a good amount of heat it energy required tohigh raise one pound of material by rapidly one degree Fahrenheit. rubbing surface. Material with highest specific heat is not necessarily the best for brakes. To be a good

brake material, it must withstand high temperature, conduct heat rapidly and have a good rubbing surface. energy when a wind-up toy car is released. Chemical energy stored in energy whenis converted a wind-up int toy car is gunpowder o sound, released. Chemical energy heat and kinetic energy when stored ignited in . gunpowder is converted intoroad sound, down the has A car moving heat andenergy. kinetic energy kinetic To stopwhen the ignited. car, you A car moving downkinetic the road has must dispose of this energy. kinetic stop bethedestroyed, car, you Becauseenergy. energy To cannot must of thistokinetic it mustdispose be converted anotherenergy. form. Because energy cannot be be destroyed, This kinetic energy could convertit be converted to another edmust into any of the forms listed onform. page This kinetic energy could convert8, but conversion to heat isbe easiest. By ed into anyfriction of the forms listed on page forcing material against 8, but conversion heatis iscreated easiest.and By drums or rotors , to heat forcing friction material against the car slows . If the brakes or tires drums, orsome rotors, heat energy is created and squeal sound is also the car slows. If the brakes or tires produced, but the amount of kinetic squeal, some sound energy isis small also energy converted to sound produced, tobut theenergy. amount of kinetic compared heat energy soundcaris using small If youconverted had an to electric compared to heat energy. batteries, you could brake the car by If you had electric car inusing converting the an electric motor to a batteries, you brake car by generator. Thiscould could be the done by converting the motor into switching the electric connections. Thea generator. could be done by motion of This the car would turn the switching putting the connections. generator, electric energy The into motion of the the the batteries. Thecarcarwould would turn s low begenerator, putting electric energy into cause power- kinetic energy in this the batteries. The car would slowelecbegenerator. Some case - turns the cause this tric carspower-kinetic maintain their energy battery in charge case-turns generator. Somecalled elecby using thistheform of braking tric cars maintain their battery charge regenerative braking. byItusing of braking wouldthis be form wonderful if fuel called could regeneralive braking. be put in the gas tank by hitting the It would be 'twonderful fuelallcould brakes. It can , however,if so that be put in the gas tank by hitting the kinetic energy is lost. On the other brakes.if Ityou can't, so allor that hand, drivehowever, more slowly ankinetic every energystop, is lost. theuseother ticipate you On could the hand, if you drive more slowly anbrakes less and, th us , conserveorfuel. ticipate every stop, you could use the Try this while driving to work. The brakes less and, conserve fuel. fuel energy used thus, to move the car is Try in thisheat while driving work. lost energy eachtotime youThe hit

fuel energy used to move the car is lost in heat energy each time you hit

the brakes. By minimizing braking , you increase mileage. theIf brakes. By the minimizing braking, you slow car without using you mileage. the increase brakes, the kinetic energy can be If you into slow two the different car without using changed forms. If the brakes, the kinetic energy can be you are driving on a flat road and take changed twothrottle, differenttheforms. If your foot into off the car will you driving on a flat road take slow.are Kinetic energy is lost in and air drag, your foot(heat) off the throttle, theand cardrive will friction in the engine slow. Kinetic energy is lost in air drag, line, and rolling resistance of the tires. friction (heat) in items the engine andkinetic drive Because these get hot, line, and rolling resistance of the tires. energy is converted into heat. Because these items slowing get hot, kinetic However, because takes energy longer andis theconverted items beinginto heatedheat. are However, slowing takes much larger,because drive-line components longer anddon't the items area nd tires reachbeing the heated high tem" much larger, drive-line components peratures achieved by the brakes. But, and tires isdon't the heat therereach . Put the yourhigh handtemon peratures by run the on brakes. But, your tires achieved after a fast the highthe heat is there. Put feel your hand the on way and see how they . Touch your tires after a fast run on the highrear-axle housing and the transway and. see how they feel. Touch mission A portion of the power of the the rear-axle and the transengine washousing lost supplying the energy A portion mission. to heat those parts. of the power of the engine was lost The other waysupplying yo u can the slowenergy a car to heat those parts. without the brakes is by coasting up a The other way you can toslow car hill. The car loses energy draga the without the brakes is by coasting up same as on a fl at road , but it slowsa hill. TheThe car kinetic loses energy drag the quicker. energyto is convertsame as on a flat road, but ed into potential energy as ittheslows car quicker.the The kinetic energy is convertclimbs hill. as another the car edPotential into potetltiol energyetiel,gy is just climbs the hill. form of stored mechanical energy. It Potential when energy is justis raised another a weight to is increased of stored greater height.mechanical As the carenergy. climbs Ita aform is increased a weight is raised to hill, some ofwhen its kinetic energy is conaverted greater height. As the car climbs to potential energy. This pote n-a hill, energy some ofcan its be kinetic energy is contial changed back into verted potential energy. kine tic to energy by all ow in gThis the potencar to tial energy back coast down can the be hillchanged with the e nginto ine kinetic energy by allowing the car of to shut off. The speed at the bottom coasthilldown hill than with the the original engine the will the be less

shut off. The speed at the bottom of the hill will be less than the original

Car parked at top of hill has zero kinetic energy. However, its position at top of the hill gives it potential Car parked at top ofenergy" hill hasThis zeropotential kinetic energy is changeditsinto kinetic as energy. However, position at energy top of the car gives coastsit down hill. energy. This potential hill potential

energy is changed into kinetic energy as car coasts down hill.

After coasting half way down the hill, car has lost half of its potential energy, but has gainedcoasting kinetic half energy. energy inAfter way Kinetic down the hill, car creases as car increases. has lost half of speed its potential energy, but has

gained kinetic energy. Kinetic energy increases as car speed increases.

All potential energy of coasting car is converted into kinetic energy at bottom of the hill where carenergy reaches speed and All potential of maximum coasting car is conkinetic verted energy. into kinetic energy at bottom of the

hill where car reaches maximum speed and

speed kinetic when energy.you began to coast up the hill because some energy is lost in fricspeed when yougoing beganuptothe coast the tion and drag hill,upplus hill energy becauselost some energy losthill. in fricthe going downisthe

tion and drag going up the hill, plus the energy lost going down the hill. 9

Tempera ture (OF)

Rubbing Surface

Temperature (" F)

Brakes Re leased

/

Temper at ure of Brakes Released

Rubbing Surface of Drum or Rotor Temperature of

,/ '\.. "

ｾ＠

T s L---__ｾＭ

Te mpe rature of I nterior of Drum or Rotorof Temperature Mater ia of l Interior

Drum or Rotor

Time of Stop

Rubbing Surface

Interior of Rotor _ Materi al

Interior of Rotor Material

In te rior of Drum Material Interior

Rotor Cross Section Rotor

Cross Section

of Drum

%

Rubbing Surface

Drum Cross Section Drum

Cross T m = Maximum temper ature reached at r ubbing surface . Section T a = Average temperature after stop. temperatur e before stop.at rubbing surface. T, s == Starting Maximum temperature reached T, = Average temperature after stop. T, = Starting temperature before stop. During a stop, brake rubbing-surface temperature increases more rapidly than interior temperature of a drum or rotor. Eventually, temperatures equalize after brake is released . Aver-I age brake temperature occurs at a point betweenincreases rubbing - more surface and than interior temperaDuring a stop, brake rubbing-surface temperature rapidly interior temtures before place. temperatures equalize after brake is released. Averperature of amuch drum cooling or rotor.takes Eventually, age brake temperature occurs at a point between rubbing-surface and interior temperatures before much cooling place. in a brake. The problem is that heat is is takes measured Potential energy

units of foot-pounds (ft-Ib). PotentialPotential energy measured in e nergy change equalsis the weight of units of foot-pounds by the Potentialchange in the object mUltiplied (ft-lb). energy equals thecoasts weightup ofa height. change If a 3000-1 b car the objectghmultiplied by the change in 100-ft-hi hill , it gains 300,000 ft-lb height. If a energy. 3000-lbIf al car coasts up isa l this energy of potential 100-ft-high back hill, itinto gains 300,000 ft-lb converted kinetic energy, of potential energy. If all this energy is the speed of the car can be calc ul ated converted back into kinetic 8. Byenergy, changfrom the formula on page the of the carusing can bealgebra, calculatedit ing speed the formula from the formula on page 8. By changcomes out as follows: ing the formula using algebra, it comes outf29.9E: as Speed ｾＭｰ＠ follows: in miles per hour We (mph) in miles per hour Ep = Potential energy of car in foot-pounds (ft-Ib) Ep = of car in (Ib) We = Potential Weight ofenergy car in pounds foot-pounds (ft-lb) W, Weight of le car Fo r=our examp , in pounds (Ib) ＬＮＢｾ［Ｍ Speed (29.9)(300 ,000) = 55 h For our=example. 3000 mp . Speed = is much faster th an Obviously, this3000 would happen if you tri ed it with a real this is much faster than car.Obviously, The difference between this would happen if you tried it sample problem and a real with test isa real the car. The difference this and friction. kinetic energy lost in dragbetween samplehot problem and aget realduring test is one the do brakes How kinetic energy lost in drag and friction. stop? -Because the brake-rubbing How hotaredoheated brakes get during it is one imsurfaces by friction, stop? -Because the thebrake-rubbing portant to know what temperature surfaces are stop heated friction, it istemimsurface is after one . P.byhigh portant to know what the temperature perature can cause fade or damage to is after one stop. P. high surface temperature can cause fade or damage to 10

=y

constantly being transferred from the afriction brake.surface The problem is that heat to is of the drum or rotor constantly being transferred from the air and cooler interior metal. This friction surface of surface the drumtemperature or rotor to makes the exact air and to cooler interior metal. This calculate. However, it is difficult makes exact surface temperature ate the average temperaeasy to the calcul difficult calculate. it is ture of a to drum or rotor However, after one stop'. easy to calculate the average temperaThe difference between surface temture of a and drum orrage rotor after one stop. perature ave temperature of a The between surface temn above. drumdifference or rotor is show perature and average temperature of a In calculating the average temperadrum or rotor is shown above. tu re of a drum or rotor, you must In calculating theptions. average temperamake so me ass um This makes ture caoflcualatidrum or rotor, youanswer must on easier and the the make some assumptions. This makes more accurate. Tests have shown that the fo calculation easier and are thevalid: answer llowing assumptions the more accurate. haveenergy shownfrom that • Assume that Tests all heat the following assumptions are valid: the stop fl ows into the drum or rotor. heatteenergy from is anall accura assum ption In Assume fact this that the stop flows into the drum or rotor. because th e frict ion material insulates In is an accurate assumption thefact rest this of the brake from heat and the because the friction material insulates metal drum or rotor is a very good the of the brake from heat and the heatrest conductor. metal drumdrag or rotor is car a very • Assume on the fromgood all heat conductor. sources is zero, including the effects on the car fromand all of Assume air drag,drag rolling resistance sourcesbraking. is zero,This including theassumpeffects is a good engine of rolling100resistance and mph because tionair for drag, stops below engine braking. This is a good assumpair drag is small compared to braking tion for stops below 100 mph because forces. air drag is kinetic small compared braking in • Ignore energy to stored forces. rotating parts of the car. This assumpIgnore kinetic energyof stored in tion and the assumption zero drag rotating parts of the car. This assumption and the assumption of zero drag

The heavier a drum or rotor, the lower its temperature rise during a single stop. Designed for a a3000-lb car lower powered The heavier drum or sports rotor, the its by a 300-HP large temperature rise engine, during a this single stop.drum Deweighs for 22 lb. signed a 3000-lb sports car powered

by a 3 0 0 - H P engine, this large drum weighs 2 2 Ib.

cause errors in opposi te directions. Thus, the error in the brakecause errorscalculation in opposite directions. is sma ll. temperature Thus, error ofinbrakes the during brake• Ignorethecooling temperature calculation is small. stop. Heat flo w into rotor or drum Ignore iscooling of brakes during to coo ling material rapid compared stop. time. Heat flow into rotor or drum material is step rapidiscompared cooling The first to calculatetothe temtime. perature change of the drum or rotor. Theincrease first step to calculate isthe temin istemperature known Any perature change of the drum or rotor. ture rise. Temperatures are as tempera Any increase in temperature is known to energy by always related as tetnperature Temperatures change -not byrise. the absolute valuesare of always or related to . It energy byt is importan energy temperature change-not by the values of to think of this as aabsolute change in energy energy or temperature. It is important in temperature. Temcausing a change change inused energy to think of this as abrake in the is ca by perat ure rise causing a change in temperature. a kinetic-energy reduction inTemthe peraturecar. rise in the brake is caused by moving a For kinetic-energy in the a particular reduction stop, figure the moving car. change in kinetic energy using th e For a onparticular stop,results figurein the the formula page 8. This change kinetic energy using the followinginrelationship: formula on page 8. This results in the = Kinetic energy change in footKe following relationship: pounds = Ks - KAin foot-pounds K c == Kinetic Kinetic energy energybefore change footKs the instop in K, - K, in foot-pounds pounds = foot-pou nds K, = the stop stop in in KA = Kinetic Kinetic energy energy before after the foot-pounds foot-pou nds K, = Kinetic energy after the stop in Obviously, if the car comes to a foot-pounds complete halt , KA is zero . The change if the car comes to comptoutea in Obviously, kinetic energy is used A is of zero. change complete halt, K rise the temperature theThe brake. For in kinetic used use to compute the weight energy of the is brake, only the the temperature rise of and/ the brake. For weight of the drums or rotors. the weight of the brake, use only the The temperature rise must be added weight of the drums and/or of the brake rotors. before to the temperature The rise must the temperature stop to obtain finabe l added brake to the temperature of the brake before temperature . the stop to obtain final brake temperature.

The temperature rise of the brakes is calculated as follows:

The temperature rise of the brakes is calculated as follows:Kc Temperature rise = - - 77.8 KcW B Temperature rise = (F) in degrees Fahrenheit 77.8the W, rotors and W B = Weight of all in degrees Fahrenheit (F) drums in pounds W, = Weight of all the rotors and For inexample, drums pounds let 's compare the

temperature rise in the brakes of a For example, let's compare the 3500-lb sedan stopping from 60 mph temperature rise in rise the of brakes of a to the temperature a 3500-lb 3500-lb sedan stopping fromfrom 60 rnph stock-car's brakes slowing 120 to the temperature rise of a 3500-lb mph to 60 mph. stock-car's from 120 First let'sbrakes figure slowing the temperature rnph to 60 rise for themph. sedan. Assume the brakes First 5let's figure forthea temperature weigh Ib each, total brake rise for the sedan. Assume the the change brakes weight of 20 lb. Calculate weigh 5 Ib each, for a total brake in kinetic energy slowing from 60 weight 20 From Ib. Calculate mph to of stop. page 8, the the change kinetic in kinetic energy car slowing from 60 energy of a moving is: rnph to stop. From page 8, the kinetic W S2

KinetiC energy = _ ccar _ is: energy of a moving 29.9 W,S2 - at 60 mph: Kinetic energy For our sedan= traveling 29.9 KB = (3500 Ib)(60 mph)2/29.9 For our sedan traveling at 60 mph: = 421,000 ft-Ib . K , = (3500 1nph)~/29.9 KB = Kineticlb)(60 energy before stop = 421,000 ft-lb. Kinetic energy after thestop stop = 0, K, = Kinetic energy before

because car now has zero speed. Kineticin energy the =stop = 0, Change kinetic after energy 421,000 because car now has zero speed. ft-Ib. From the above formula temChange perature in risekinetic of the energy brakes is:= 421,000

ft-lb. From the above formula tem. _ (421,000 ft-Ib) perature rise rise of the is: Ib) Temperature - brakes (77.8)(20

Tires on this car have reached their maximum coefficient of friction. Although a car stops faster if the wheels are not locked, most drivers hit the brakes too hard during a panic stop. This being at Goodyear's San Angelo, Texas, test track, is to see howstops tires Tirestest, on this carconducted have reached their maximum coefficient of friction. Although a car react during a paniC are stop.not Photo courtesy Goodyear. faster if the wheels locked, most drivers hit the brakes too hard during a panic stop.

This test, being conducted at Goodyear's San Angelo, Texas, test track, is to see how tires react during a panic stop. Photo courtesy Goodyear.

time, racing on a medium-speed track with short straights might result in time, racing a medium-speed tracka higher brakeon temperatu res than with short straights might result in high-speed track with long straights. higher brake temperatures than Both temperature rise per stop anda high-speed track long to straights. cooling time arewith critical brake Both temperature riseweighing per stopmore and performance. Rotors cooling time are critical to brake than 5 Ib would normally be used on a performance. weighing rotors more 3500-lb race Rotors car. Heavier than 5 Ib normallyrisebeper used on a reduce thewould temperature stop.

3500-lb race car. Heavier rotors

reduce the temperature rise per stop. DECELERATION Deceleration is a measure of how

DECELERATION quickly a car slows. Deceleration (77,i)(20 Decele~.a/ion is a measure of how

(421 000 ft-lb) Temperature rise = = 270F (132C)

For stock car slowing from 120 to 60 mph, change in kinetic energy is:

For stock car slowing from 120 to 60 K = (3500 Ib)(1 20 mph)2 mph, B change 29.9in kinetic energy is: (3500 IbI(l20 = 1,686,000 ft-IbmphI2 K, = 29.9 K = (3500 Ib)(60 mph)2 A = 1,686,000 29.9 ft-lb (3500 lb)(60 = 421,000 ft-Ib rnphI2 K, = 29.9 Kc = KB - KA = 421,000 ft-lb Kc = (1,686,000) - (421,000) Kc = 1,265,000 ft-Ib. KA energy K, == Kinetic 1,265,000 ft-lb.after stop KB = Kinetic energy before stop K, = energy after stop Kc = Kinetic Kinetic-energy change K, Notice = Kinetic energy before stop how much greater this change Kc = Kinetic-energy change in kinetic energy is compared

howEven much greater this to Notice the sedan. though the speed change in was kinetic is compared reduction the energy same 60 mph, the to the reduction sedan. Even thoughatthe speed speed occurring a higher reduction was the same 60 mph, the initial speed resulted in much greater speed reduction occurring a higher energy put into the brakes at . The teminitial speed in much perature rise resulted for the stock car greater in the energy put into the brakes. The temrace is: perature rise for the stock car in the Temperature rise = (1,265,000 ftrace is: Ib)/(77.8)(20Ib) = 813F (434C). Temperature rise = of (1,265,000 ftHowever, because less cooling lb)/(77.8)(20Ib) = 81 3F (434C).

However, because of less cooling

means slowing the car-acceleration

quickly a car itslows. Deceleration means speeding up. means the car-acceleration Both slowing acceleration and deceleration means speedinginit units up. of gravity-g's. are measured Both acceleration and deceleration One g is the force exerted by an object are in units gravity-g's. due measured to gravity at ofthe Earth ' s One g is the exerted by anweighs object surfacehowforce much an object due to gravity at the Earth's while at rest. One g is also a measure surface-how object weighs of accelerationmuch or an deceleration - 22 while at rest. One Zero g is also a measure mph per second. g occurs in a of acceleration or deceleration-22 weightless environment. Acceleration rnph per second. Zero isg negative. occurs in a is positive; deceleration weightless environment. Acceleration Once the brakes are applied, a car is is positive; negative. stopped by deceleration the friction is force between the brakes are applied, a car is theOnce tires and the road. During stopped by the friction force between braking, friction acts on the tires in a the tiresopposite and the road. During direction to movement. The braking,the friction acts on the in a higher deceleration, thetires greater direction opposite to movement. The this friction force becomes . Maximum higher the deceleration, the greater possible deceleration occurs at the this friction force becomes. Maximum maximum coefficient of /riction bepossible occursThis at hapthe tween the deceleration tires and the road. maximum fiiction bepens just as coeflicient the tires areofabout to skid. tween the tires and the road. This hapOnce tires lose traction and skid, pens just as the tires are about deceleration drops. Read on to forskid. an Once tires of losecoefficient traction ofand skid, explanation friction, deceleration drops. Read on for an or si mply friction coefftcient. explanation of coefficient of friction, or simply ,f,.ictiot7 coeJficient.

INERTIA FORCES

More than 200 years ago, Sir Isaac INERTIA FORCES Newton wrote the basic law relating a More 200 years Sir Isaac force on than an object to itsago, acceleration. Newton wrote Newton's the basic Law law relating a Simply stated, is:

force on an object to its acceleration. Acceleration of an object = ｾ＠ in g's Simply stated, Newton's Law is:

F of an object in g's in Acceleration force = on object F = Unbalanced pounds F == Weight Unbalanced force on object in W of object in pounds pounds In this formula, the force F causes W = Weight of object in pounds

acceleration. If a car weighing 3000 Ib formula, causes hasIna this braking forcethe of force -1500F lb, the acceleration. weighing 3000 Ib Ib stopping forceIf isa car -1500 Ib -7- 3000 has a braking force of 1500 Ib, the = -0.5 g. stopping force pushes is - 1500 + 3000 to Ib If the force in aIbdirection = -0.5theg.object to speed up , the force cause the force in a direction to is If positive andpushes acceleration is a posicause the object to speed up, the force tive number. If the force causes the is positive and acceleration a posiobject to slow, the force is isnegative tive number. If the force causes the and acceleration is negative. We call object to slow, the force is negative the negative acceleration deceleration . and acceleration is negative. We call The force referred to in Newton's the acceleration Lawnegative is unbalanced force. decele~.arion. That means Theforce forceis referred to inby Newton's if the not resisted opposing unbalanced force. That means Law is force, the object is free to move, or if the force is not resisted by opposing accelerate. If I push on a tree with a force, freewill to not move, or force ofthe 100object Ib, theistree move. accelerate. I push on a tree with The 100-lb If force is resisted by the treea force 100a Ib, the tree will so notthere move. roots of with 100-lb force, is The 100-lb force is resisted by the no unbalanced force on the tree.tree To roots with a 100-lb either force, positive so there or is cause acceleration, no unbalanced force tree. To negative, the force on on the the object must cause acceleration, either positive or be unbalanced. negative, the force on the object must To understand how unbalanced be unbalanced. forces work on a car, assume you are To understand how strip. unbalanced driving a car on a drag At the forces work on a car, assume youpush are start, you let out the clutch and drivingona the car accelerator, on a drag strip. At fricthe down and the start, you let out thetheclutch tion force between tires and and push road down on the accelerator, and thestart, fricpushes the car forward . At the

tion force between the tires and road pushes the car forward. At the start, 11

air drag is zero, so the forward force is not resisted by anything but drive-line friction and tire drag, or rolling resistance. The forward force is almost unbalanced. Consequently, acstart. celeration is maximum at the start. As the car gains speed, air drag increases. It opposes the forward force on the tires that is trying to accelerate the car. The unbalanced force is the forward force minus the rearward force. As speed increases, the unbalanced force becomes smaller because of air drag. Consequently, acceleration also gets smaller. Near the end of the drag strip, the car is moving so fast that the air-drag force approaches the forward force of the tires against the road. Assuming engine rpm and track length aren't limiting factors, factors, speed will increase until no force unbalance exists and acceleration becomes zero. The car has reached its maximum speed. The only way to accelerate the car to a higher speed would be to increase the forward force (more engine power), or reduce (Jess air drag). the rearward force (less drag). Every race-car designer knows that more power or less drag will increase car speed. speed. In addition to the basic relationship between force force and acceleration, Newton came up with other important laws of of nature. nature. He t l e discovered that every moving object has inertia. That is, an object always always moves at the same same speed and in the same same direction until acted on by an unbalanced force. force. Inertia is is what keeps the Earth moving around the Sun and keeps satellites in orbit. orbit. There is no air drag in outer space, space, so so once an an object is is at speed, it keeps moving forever. forever. Only a force force can change its speed or direction. direction. A car also acts acts according to Newton's laws. laws. Once Once it is moving, a car wants to continue in a straight line line at the the same same speed. speed. Every part of the the car and its passengers also want to keep moving. moving. When the brakes are applied, applied, a force force is is applied to to the the car by the tires, causing deceleration. deceleration. Because Because passengers passengers tend to to continue at the the same same speed, speed, they will will move forward forward in in the seat seat and strike strike the the instrument panel unless held by restraint devices, devices, legs or friction friction against the the seat. seat. This This forward forward force force that tends tends to to "throw" "throw" a passenger forforward during during braking is is called called inertia force. ,force. Inertia force force acts acts on on everything in in aa car as as its its speed speed changes. changes. 12

--

. . Inertia Force

Friction Forces ForCes on Tires Friction

-

-

Tire friction forces are external forces that cause deceleration. deceleration. The road road pushes pushes on the opposite direction direction of motion. tires in in the opposite motion. Inertia lnertia force of the car acts in the same direction as motion equals friction friction force. force. motion and equals

Therefore, if a car accelerates, the inertia force acts toward the rear; if it decelerates, the inertia force acts forward. forward. Inertia force in g's is equal to car's car's acceleration or deceleration. deceleration. Inertia forces are easy to calculate in pounds if you know the acceleration. acceleration. W object in W == Weight of the theobject in pounds a= = Acceleration of the object in in g's

Inertia force is measured in pounds. If the car is decelerating, decelerating, the inertia force is negative-it negative-it acts in a forward direction. direction. Try visualizing visualizing what happens when a car decelerates. decelerates. It is easier to visualize the forces if you imagine a driver trying to stop stop so so quickly that he locks the wheels. wheels. Imagine a car skidding with all all four wheels locked and smoke smoke pouring off the the tires. tires. Assume the the car weighs 3000 lb Ib and the coefficient of friction friction between the tires and road is is 0.7. The The friction friction force force on all all four tires 0.7. is: is: Friction p FN FN Friction force == f.L p = = Coefficient Coefficient of friction friction between between two f.L

Inertia lnertia forces forces act on on every every part of a car. car. This passenger resists resists inertia inertia force on on his his This body with his his arms arms against the the dash, dash, feet body against the floor, floor, and and seat belt around around his his against waist. waist. Inertia lnertia force force on on his his hat is is not not resisted by by anything, anything, so so it it flies flies forward forward into into the ed windshield. windshield.

Acceleration of car == F F/Wc IW c F == Unbalanced Unbalanced force forceon in pounds ~ounds F on car in We Wc == Weight of car in in pounds pounds

Acceleration of of car Acceleration Ib) == -0.7 -0.7 g. g. Ib)

= =

00 Ib)/(3000 lb)/(3000 (-2100

Friction Friction force force = = (0.7)(3000 (0.7)(3000 Ib) Ib) = = 2100 lb. Ib.

The unbalanced force force has a minus minus The sign because it acts acts in in a direction direction sign car. Remember: Remember: Negaopposite to the car. tive acceleration means deceleration; deceleration; tive car to to slow. slow. itit causes the car deceleration is is 0.7 0.7 g, E., every everv Because deceleration part of the car has an inertia force force on it g. The inertia force force on a 200-lb of 0.7 g. passenger is: is: passenger

This This friction friction force force on the the tires tries tries to to decelerate decelerate the the car. car. The The deceleration deceleration is is easy to calculate calculate from from Newton's law, law, easy page 11: 11:

Inertia lnertia force force == Wa Wa w == Weight Weight of of the the passenger passenger in in W pounds pounds Acceleration of the the passenger passenger in in aa == Acceleration g's g's

sliding surfaces sliding FN Force pushing pushing the the two surfaces F, == Force together in nds in pou pounds

In this this example, example, p == 0.7 0.7 and and FN FN== 3000lb 3000 Ib f.L

-

- - -

~

~-~

If there were some way to support a car at its center of gravity (CG), it would be balanced. Rotate the tocar to another If there were some way support a car at position, as on a (CG), side, and it would its centersuch of gravity i t would be remain balanced. CGcar is the supbalanced. RotateThe the to only another port pointsuch where exists regardless position, asbalance on a side, and it would of position. remain balanced. The CG is the only sup-

port point where balance exists regardless of position. I nertia force = (200 Ib) (-0. 7 g) =-140Ib.

Inertia force = (200 Ib)(-0.7g) The minus = sign the force is -1 40means Ib. forward. If there is little friction beThe sign means the seat, forcethe is tweenminus the passenger and the forward. If there is little friction be140-lb inerti a force acts on his seat tween belt or the legs.passenger and the seat, the 140-lb forcetheacts his seat In thisinertia example, car on decelerates belt or legs. at only 0.7 g. With the wheels locked In sliding, this example, the car decelerates and the coefficient of friction at g. With the wheelspossible locked is only lower0.7 th an its maximum and sliding, the coefficient of friction value. Maximum deceleration of a car is determined lower than by itsmany maximum lis factors,possible includvalue. Maximum deceleration car aerodynamic forces,of aroad ing tires, pis determined by many factors, includcondition and brake-system design. ing tires, forces, road Most cars aerodynamic on street tires can reach condition and deceleration brake-system on design. about 0.8-g dry Most cars Race on street tires can reach pavement. cars can decelerate at about well over0.8-g 1 g. deceleration on dry pavement. Race cars can decelerate at well over 1 g. WEIGHT TRANSFER A car's inertia force acts at its center

WEIGHT TRANSFER of gravity, or CG, of the whole cal'. The

forcewhich acts atthe its entire center CGA iscar's the inertia point about of graviry, or CG, of the whole car, car is balanced. If you could hang The the CG by is the pointattached about which car a cable a t itsthe CGentire , the car would is balanced. you hang the car balanceIf in anycould position. carThe by aCG cable at its is attached the center ofCG, all the the car would balance in any position. weight. All the inertia forces on the inof togethall the The CG dividual partsis ofthe the center car added weight. inertia on the iner are All the the same as forces a single inertia dividual parts of the car added togethforce for the whole car acting at its er the same as a CO single inertia CG.areBecause a car's is always force for whole car acting its above thethe road, inertia force at from CG. Because car'sto CG braking always atries load isthealways front above theliftroad, inertia force from tires and the rears . This effect is brakingweight always tries to load the front transfer. called tires and lift the rears. This that effectthe is Weight transfer means called weightare transfer. front tires loaded more during a Weight transfer means that the stop, and the rear tires are unloaded.

front tires are loaded more during a stop, and the rear tires are unloaded.

A front-wheel-drive car, such as this VW, has majority of weight at front. When brakes are applied hard, more weight is transferred to the front. The nose drops and tail rises during braking due to weightcar, transfer. A front-wheel-drive such as this VW, has majority of weight at front. When brakes are

applied hard, more weight is transferred to the front. The nose drops and tail rises during braking due to weight transfer.

t ｾｉ＠

F, = vertical force on front tires Ob) F, = vertical force on rear tires (Ib) Xeg horizontal Ff ==vertical forcedistance on frontfrom tiresfront (Ib) axle to CG .) F, =(in vertical force on rear tires (Ib) I = wheelbase length (in.) from front axle to Xcg = horizontal distance Y CG height (in.) CG (in.) eg = (Ib) (in.) We Car weight I = =wheelbase length fJ. == Coefficient friction Ycg CG heightof(in.) Wc = Car weight (Ib)

F

,

=

W _F e

,

+ We fJ.I Y cg

wc P YYCg I eg F =WcXCg·_W c fJ.Y 'I I wc xc;WC P Ycg F, = I I Yea Weight transfer = W efJ.

Ff=Wc-F,+-

I

Weight transfer

= Wcfi

Ycq

p. = Coefficient of friction I Ignoring aerodynamic forces, these forces act on a car during hard braking. Maximum weight transfer can be calculated if tire coefficient of friction is known.

Ignoring aerodynamic forces, these forces act on a car during hard braking. Maximum weight transfer can be calculated if tire coefficient of friction is known.

The weight of the whole car does not change. Weight added to the front The of the whole car rear doestires not is subtracted from the tires weight change. Weight added to the front during weight transfer. The forces tires is on subtracted from the rear tires a car during braking are acting during transfer. Thedrawing forces. shown inweight the accompanying acting on a car during aerodynambraking are In this simple illustration, shown in the accompanying drawing. ic forces are not shown. Aerodynamic In this simple aerodynamforces changeillustration, the amount of the ic forcesbut arenot not the shown. forces, basicAerodynamic principle of forces change the amount of the weight transfer. forces, but weight not thetransfer basic principle of Because loads the weight transfer. front tires, additional friction force weight transfer loads tires the canBecause be developed by the front

front tires, additional friction force can be developed by the front tires

before they skid. To produce this extra friction force, front brakes have before skid. produce to work they harder thanToif there was this no extra force, front brakes weightfriction transfer. At the same time,have the to hardercan than do if there no rearwork brakes less was work. weight transfer. At the same time, the Typically, front brakes supply about rear brakes less force work. two-thirds of thecan totaldo braking in Typically, front about Thebrakes ratio issupply even higher a hard stop. two-thirds of the total braking car. forceBein on an extremely nose-heavy acause hard the stop. T h e ratio is even higher front brakes do most of the on an they extremely car. rear Bework, need tonose-heavy be larger than cause front brakes most higher of the brakes.the The forces are do usually work, they need to larger than rear on front brakes, so be they must absorb brakes. The forces are usually higher more heat energy.

on front brakes, so they must absorb more heat energy. 13

BRAKE FADE Brake fade is loss of braking due to overheating. It can cause lo'nger pedal travel as the brakes get hotter-maybe to the paint where the pedal goes to the floor. Pedal effort may also increase as heat bu'ilds up, even to the point where pushing with maximum force won't lock the wheels! Many times, fade causes a combination of both longer pedal travel and increased pedal effort. Whatever fade is, the driver is faced with a panic situation. Brake fade typically occurs at the worst posSible moment-going down a long hill pulling a trailer, at the end of a long race, or during a panic stop from freeway speed in heavy traffic. This is when you need your brakes the most. Consequently, brake fade is always scary, and often dangerous.

Geoff Brabham is at the traction limit of his Toyota Celica in this turn. Combination of braking and cornering forces causes tires to slip and pOint at extreme angles to the direction of travel. When carisisatat tractionlimit limit, attempt to corner, or brakeofharder Geoff Brabham theitstraction of any his Toyota Celica in thisaccelerate turn. Combination brakwill throw it into a forces skid. causes tires to slip and point at extreme angles to the direction of ing and cornering

travel. When car is at its traction limit, any attempt to corner, accelerate or brake harder will throw it into a skid.

BRAKING LIMITS With a modern brake system, how BRAKING LIMITS good can brakes be? What determines a modern brakeperformance? system, how theWith limits to brake good can brakes be? What determines What makes your car stop quicker the limits than the nextto car,brake or vice performance? versa? What quicker Theremakes are your limits car thatstop determine than the next car, or vice versa? how quick a car can stop. Some of There arecanlimits that determine these limits be altered by design how quick a car can Somelaws of or maintenance, so onlystop. the basic these limits cana car be ' altered by ability. design of nature limit s stopping or maintenance, so only Brake-performance limitsthe are:basic laws of l.nature limit a car's stopping ability. Force Brake-performance limits are: 2. Deflection 1. Wear Force 3. 2. Deflection 4. Temperature 3. Wear 5. Tire traction

4. Temperature 5. A Tire braketraction system should be designed

and maintained so that tire traction A brake system should your be designed determines how quickly car can and maintained so other that tire stop. If any of the fourtraction limits determines howstopping quickly quicker, your caryour can keep you from stop. any the other four limits brakesIfare notofadequate. keep you from your Force limit stopping means quicker, the driver brakes are not adequate. pushes as hard as possible with his Force means foot and limit the car can't the stopdriver any pushes as possible with his quicker. In hard otheraswords, if the driver foot carthecan't stop stop any could and push the harder, car would quicker. This In other the driver quicker. limitwords, can beif altered by

could push harder, the car would stop quicker. This limit can be altered by

14

reducing master-cylinder size, putting on different lining, using power-assist reducing size,I putting brakes, ormaster-cylinder other methods. discuss on different lining, using power-assist how to reduce the force a driver has to brakes,later or inother methods. I discuss exert the book. In some cases, to reduce the force a driver has to ahow force limit occurs when the brakes exert later in the book. In some get hot . This is called brake fade.cases, The a force limit occurs when the answer here is dissipating heat.brakes Perget brake fade. The hapshot. theThis forceis called limit you've encounanswer is dissipating heat. limit. Pertered is here really a temperature haps to the forceexcess limit heat you've encounHow handle is discussed tered is really a temperature limit. in Chapters 10 and 12. How to handlelimit excess is discussed Deflection is heat reached as the in Chapters andat12. brake pedal 10 stops the floor or stop. Deflection limit is reached as the This means the pedal is moving too brake pedal stops at the floor or stop. far to get maximum efficiency from This means Athedeflection pedal is limit moving the brakes. can too be far to get maximum efficiency from eliminated by design changes such as deflection limit can be the brakes.theA pedal-support stiffening structure, eliminated design changessize, such inas increasing by master-cylinder stiffeningstiffer the pedal-support stalling brake hoses , structure, changing increasing master-cylinder size, into stiffer calipers, or other modistalling stiffer brake hoses, changing fications. Maintenance can eliminate stiffer calipers, other modiato deflection limit if or air is trapped in fications. Maintenance can eliminate the brake lines. a deflection limit if airhappen is trapped in Wear limit won't when the brake lines. brakes are new. However, if friction Wear limit happen it when material is wornwon't excessively, may brakes friction be wornare outnew. just However, when you ifneed the material is worn excessively, it may brakes most-such as at the end of a

be worn out just when you need the brakes most-such as a t the end of a

long race. Wear limits can be eliminated or reduced by changing linings, long Wear limitsorcanbybedissipating eliminatusingrace. larger brakes, ed reduced changing inlinings, wear by is discussed Chapheat.orBrake using larger ters 4 and 12. brakes, or by dissipating heat. Brake wearlimit: is discussed ChapTemperature Brakesincannot ters 4 and absorb the12.full power of an engine Temperaturewithout limit: some Brakes time cannot continuously to absorb the full power of an engine is cool. When the temperature limit continuously without time to reached , you can reachsome a force limit, cool. Whenlimit, the temperature limit is deflection or greatly increase reached, you can reach a force limit, the wear at the same time. Other deflection limit, or greatly increase things can happen , too , such as comthe at theofsame time. orOther pletewear destruction the brakes total things can too,part. suchExcessive as comof ahappen, structural collapse plete destruction. the brakescause or total temperature is aofcommon of collapse of a structural part. Excessive brake problems. temperature is a Ifcommon of Traction limit: brakes arecause properbrake problems. ly designed and maintained, and don't If brakes are propergetTraction too hot,limit: the only stopping limit is ly maintained, and don't tiredesigned traction.and If you try to stop quicker get hot,traction the onlylimit stopping limitthe is thantoothe allows, If you try to stop quicker tjre traction. wheels lock up and the tires skid. The than thelimit traction limittheallows, the traction is always limit with wheelsbrakes, lock upbut andit the The good cantires be skid. increased the limit with traction is always through limit correct adjustment of brake good brakes, but it can be increased balance. Adjusting brake balance is through correct adjustment of brake discussed in Chapter 10. Modificabrake balance is balance. tions to Adjusting allow brake-balance adjustdiscussed in Chapter 10. Modificament are described in Chapter 12.

tions to allow brake-balance adjustment are described in Chapter 1 2 .

2

DrumBrakes

Drum Brakes Backing

ｐｉＢ･ｾ＠ Hole Covers

ｾ＠

ｾ＠

ｾ＠

!;

Wheel Cylinder Assembly

&(

)

Anchor-Pin Plate

ｾ＠

Secondary

fJ

a ｾ＠

Hold-Down Pin or Rod

Adjusting Lever

Return Spring

rr;;

r

Cup

Spring Retainer

Retainer

hoe Hold-Down

Modern drum brake automatically adjusts shoes outward as friction material wears. Drum is not shown. Drawing courtesy Chrysler Corporation. Modern drum brake automatically adjusts shoes outward as friction material wears. Drum is not shown. Drawing courtesy Chrysler Most cars have used internal drum Corporation.

brakes over the years. They continue carson have to Most be used theused rear internal of most drum road brakes over the years. They continue cars. to Even be used on thedrum rear brakes of most share road though cars. common features, details may differ. Even Each hasthough a metaldrum drum,brakes usuallyshare cast common iron. Thefeatures, drum details rotates may withdjffer. the Each a metalthedrum, cast wheel.has Within drumusually are brake iron. The with drum rotates with This the shoes lined friction material. wheel. Within the drum are brake material, consisting of various organic lined with friction material. This shoesmetallic and compounds, is the brake material, consisting of various organic lining. The brake shoes are moved and metallic compounds, is thebybrake against the inside of the drum pis*The brake shoes are moved lining. tons inside the wheel cylinders. Hyagainst the of the drum by draulic fluidinside under pressure in pisthe Hytons inside the wheel wheel cylinders moves cylinders. the pistons. draulic fluid under in the Wheel cylinders and pressure brake shoes are wheel cylinders moves the pistons. mounted on a metal backing plate. Wheelbacking cylinders and isbrake shoes are This plate bolted to the plate. mounted a metal orbacking car's axleonhousing suspension This backing plate is bolted to the upright.

car's axle housing or suspension upright.

Cable Guide

ｾ＠

Cable Guide

Adjuster cable!

""

Adjuster-Lever Spring

I

rgIiUli€l4S---' Pa ingBrake Strut " t" Ad JUS 109 Shoe Hold-down Parts

ｎｴＯｾ＠

Pivot u

Adjusting Screw Automatic-Adjuster Parts

Shoe Hold-down Parts Automatic-Adjuster Parts Bendix duo-servo rear brake is typical of drum brakes found on American cars. Brake features automatic adjuster and high servo action. Included is linkage to operate shoes from the parking-brake Drawing courtesy Bendix Corp.found on American cars. Brake feaBendix duo-servo cable. rear brake is typical of drum brakes tures automatic adjuster and high servo action. Included is linkage t o operate shoes from the parking-brake cable. Drawing courtesy Bendix Corp.

15

r

Trailing Shoe

Leading Shoe

Wheei Cylinder Hydraulic Force

\Trailing

Shoe

Pressurized Hydraulic on Leading Shoe Fluid r Hvdraulicｾｌ･｡､ｩｮｧ＠ Force ｾ＠ Shoe

Friction Force on Friction Trailing Force Shoe on

Trailing Shoe Pivots Away From Drum

Friction Force on Leading Shoe

Trailing Shoe

ｾ＠

I

L ~ h o Pivots e Single leading-shoe drum brake-sometimes called a lea dingand-trailing-shoe brake-has one leading and one trailing shoe. As drum clockwise, friction force on leading shoea forces it Singlerotates leading-shoe drum brake-sometimes called leadingagainst drum, creating servo one action, or force multiplication. Drum and-trailing-shoe brake-has leading and one trailing shoe. As rotation tends clockwise, to reduce shoe-to-drum of trailing shoe. drum rotates friction forceforce on leading shoe forces it

I

against drum, creating servo action, or force multiplication. Drum rotation tends to reduce shoe-to-drum force of trailing shoe.

1// ｾｆｲｩ｣ｴｯｮ＠

'Leading Shoe Pivots Toward Drum

Force on Shoe

Drum Rotation

Drum

Shoes in this single leading-shoe brake both pivot toward the right Rotation when acted on by friction forces. Although wheel-cylinder force keeps both the drum, friction forces modify Shoes in thisshoes singleagainst leading-shoe brake both pivot toward thepresright sure shoe. Leading-shoe pressure increases; when exerted acted onbybyeach friction forces. Although wheel-cylinder force trailing-shoe pressure decreases. is forces little overall keeps both shoes against the drum,There friction modify servo presaction with thisbytype of shoe. brake, Leading-shoe as friction-force effectsincreases; on shoes sure exerted each pressure cancel out each other. decreases. There is little overall servo trailing-shoe pressure

action with this type of brake, as friction-force effects on shoes cancel out each other.

SERVO ACTION There are many varIatIOns of SERVO ACTION design. Designs simple drum-brake There variations of differ in are the many amount of forcesimple drum-brake design. Designs multiplication, or servo action . Imagine forcediffer amount of brakes driving in one the car with standard servo action. multiplication, and another or equipped with Imagine powerdriving one car withamount standardofbrakes assist brakes . The pedal and another equipped force is greatly reduced with with powerpowerassist brakes. Servo The amount of much pedal assist brakes. action acts force is greatly reduced withthepowerlike power assist-it reduces force assist brakes. Servobrake actionpedal acts much required on the for a reducesHowever, the force like power assistof- itbraking. given amount required on the brake pedal for a servo action occurs within the brake given itself. amount of braking. However, servo action occurs withinhelp theunderbrake Leading or Trailing-To itself. stand servo action, let's look at how or Trailing-To under-a Leading brake shoes are mounted.help Imagine stand look howa brake servo shoe piaction, voting let's at one endatand brake shoes are mounted. Imagine wheel cylinder pushing on the other.a brake shoe pivoting at mount one enda brake and a There are two ways to wheel ascylinder the other. shoe, leading pushing shoe or ason/railing shoe. Theredepends are two ways to mount This on which end aofbrake the shoe, aspivots leaditillginshoe or as trailing shoe. shoe relation to drum This depends whichdrum end rotates of the rotation . If theonbrake shoe pivots in relation to end drum from the free (wheel-cylinder) of rotation. If the brake drum rotates the shoe toward the pivoted end, it is from the free (wheel-cylinder) of a leading shoe. If the brake end drum the shoeistoward the pivot pivoted it is motion from the endend, toward atheleading shoe. If the brake drum free end, the shoe is trailing. motion is from the pivot end applied toward Now let's look at the forces the free end, the shoe is trailing. to each type of brake-shoe arNow let's The look at the forces rangement. friction forceapplied on a to eachshoe type arleading tendsof to brake-shoe rotate the shoe rangement. The friction force on around its pivot and against the drum.a leading shoethe tends to rotate theinshoe This assists wheel cylinder ap-

around its pivot and against the drum. This assists the wheel cylinder in ap16

Single leading-shoe found on rear wheels has low leading-shoe servo action, Single in bothon directions. found rear wheels

brake is generally only. Although brake itbrake works is equally well generally

only. Although brake has low servo action, it works equally well in both directions.

plying the brake shoe. A trailing shoe is just the opposite-the friction force plying shoe.from A trailing shoe moves the the brake shoe away the drum, is just the opposite-the friction force thus counteracting the force of the moves the shoe away from the drum, wheel cylinder. thus counteracting the drum forcerotation of the With a leading shoe, wheel cylinder. increases pressure between the shoe With a leading drum rotation and drum, givingshoe, increased friction increases pressure between theaction. shoe and braking force. This is servo and driver drum, doesn't giving increased friction The have to push the and force. Thisa isleading-shoe servo action. pedalbraking as hard with The have the to push the drumdriver brake.doesn't It is just opposite pedal as hard with a leading-shoe with a trailing-shoe brake. The driver drum brake. It hard. is just the opposite has to push very with a trailing-shoe brake.leading-shoe The driver When car with has to push very hard. brakes on all wheels is backed up, the

a

When a car with leading-shoe brakes on all wheels is backed up, the

reversed direction of the wheel rotation changes all the leading shoes into reversed direction the wheel trailing shoes. The of driver noticesrotathis tiona changes all the leading as huge increase in pedalshoes forceinto retrailing toshoes. Thecar. driver this quired stop the For notices this reason, as a huge increase in pedal of force redrum brakes have a mixture leading quired to stop the -car. For this reason, and trailing shoes two leading shoes drum a mixture of leading leading on thebrakes front have wheels and one and trailing shoes-two leading and one trailing shoe on eachshoes rear on the front wheelssome and one leading wheel. This gives amount of and one trailing shoe on one eachsetrear servo action and still allows of wheel. toThis some shoes amount of shoes workgives as leading when servo action and still allows one set of braking in reverse. shoes to work as leading when Duo-Servo-Another typeshoes of brake, braking in reverse. which differs from leading- or trailingDuo-Servotype of brake, shoe types, Another is the duo-servo drum which differs from leadingbrake. Its features are shownorintrailingthe acshoe types, drawing. is the duo-servo drum companying brake. featuresbrake are shown acThe Its duo-servo does in notthe have companying drawing. a simple pivot on its brake shoes. The The are duo-servo brake have shoes connected to does each not other at athe simple on its shoes. The end pivot opposite thebrake wheel cylinder shoes are connected to link eachtransmits other at by a floating link. This the end opposite the wheel the force and motion of one cylinder shoe to by floating link. linkpin transmits the aother shoe. AnThis anchor next to the motionkeeps of one to the force wheeland cylinder theshoe shoes the shoe.with An anchor pin next to fromother rotating the brake drum. the wheel cylinder keeps the shoes The two shoes are called the primary from rotating with the shoe. brakeThe drum. the secondaty prishoe and primary The shoes are called mary two shoe pushes on thethe secondary shoe and the secondary The prishoe through the link; shoe. the secondary mary shoe pushes on the secondary shoe pushes on the anchor pin. When shoe through the link; the secondary braking in reverse, the action reverses shoethe pushes onchange the anchor When and shoes roles.pin. The pribraking in reverse, the action reverses mary shoe then becomes a secondary and the shoes shoe in the way change it works.roles. The pri-

mary shoe then becomes a secondary shoe in the way it works.

Anchor Pin

Anchor Pin

Anchor Pin

Anchor Pin rimaf hoe

Forward Braking Typical duo-servo front brake used on large front-engine, rear-drive American cars; pin is front above brake wheel used cylinder. Typicalanchor duo-servo on Adjuster joins lower rear-drive ends of shoes. Only large front-engine, American .cars; rigid connection between backing plate anchor pin is above wheel cylinder, and shoesjoins is at anchor pin. of shoes. Only Adjuster lower ends

rigid connection between backing plate and shoes is at anchor pin.

Duo-servo brakes have servo action regardless of rotation. The Duo-servo brakes have forward servo brake is designed for mostly action regardless of rotation. motion or rotation. Lining wearThe is brake is designed forward equalized betweenforthemostly primary and motion or shoes rotation.by Lining is secondary puttingwear more equalized between the primary and lining on .the face of the secondary secondary shoes the by driver puttingcanmore shoe. However, feel liningdifference on .the face of theaction secondary when little in servo shoe. driver can feel brakingHowever, in reversethe . Duo-servo brakes little difference in servo action when were used on most American cars brakingrear-wheel in reverse. drive Duo-servo with and brakes drum were onthe most cars brakesused before use American of disc brakes. with rear-wheel duo-servo drive brakesand havedrum the Because brakes before the use disc well brakes. most servo action, theyofwork on Because brakes have the heavy carsduo-servo . most action, they work well the on Pedal servo Effort-Let' s compare heavy three cars. types of brake-shoe arrangePedal Effort-Let's compare ments and see how the servo action the afthree types of brake-shoe fects pedal effort. Pedal effortarrangeis the mentsthe anddriver see how the servo action afforce applies to the pedal. fects effort. Pedal effort the accompanying ch art , it is isobviIn thepedal forcethat thethe driver appliesbrake to thehaspedal. ous duo-servo less In the accompanying chart, is obvipedal effort for a given it rate of ous that the duo-servo brake has less deceleration. pedal for bad a given rate of Now effort comes the part-we never deceleration. get something for nothing. Let 's see Nowhappens comes the bad brakes part-we getnever what when too get nothing. Let's see brake-lining material, hot. something With most for what happens when with brakesincreasing get too friction decreases hot. With most brake-lining material, temperature. As an example, assume friction decreases withbetween increasing the friction coefficient the temperature. As lining an example, assume brake drum and drops from 0.5 the between the gets hot. The comparito 0.4friction when itcoefficient brakeisdrum andinlining from 0.5 son shown the drops accompanying to 0.4 when it gets hot. The comparitable for each type of drum brake . The son is shown the loses accompanying duo-servo druminbrake the most table for force. each type of ,drum brake. The braking Thus the brake that duo-servo drum brake servo loses actiontheis most also has the greatest braking Thus, the one force. affected the the mostbrake by a that dehas thein greatest crease friction . servo action is also

the one affected the most by a decrease in friction.

Primary Shoe

Reverse Braking

Forward Braking Duo-servo drum-brake operation: Notice that primary shoe Reverse is pushedBraking away from anchor pin in forward braking. It moves until it is stopped against the drum. When backing up, rotation reverses and other shoeoperation: acts as primary courtesy Bendix Corp. Duo-servo drum-brake Noticeshoe. that Drawing primary shoe is pushed away from anchor pin in forward braking. I t moves until i t is stopped against the drum. When backing up, rotation reverses and other shoe acts as primary shoe. Drawing courtesy Bendix Corp. 160 Single Leading-Shoe or Leading-and- TrailingShoe Brake SingleDrum Leading-Shoe or

140

Leading-and-TrailingShoe Drum Brake 120

Two Leading-Shoe Drum Brake

Two Leading-Shoe

100 Pedal Effort

80

(I b)

60

40 40 -

20

20 .2

.3

.4

I

I

I Lining Coefficient of Friction

.5 I I

.4 .5 Duo-servo drum brake gives lowest pedal effort for all practical friction coefficients. Lining Coefficient of Friction .2

.3

Duo-servo drum brake gives lowest pedal effort for all practical friction coefficients.

Pedal Effort at

Pedal Effort at

Percent Increase

CF=O.5 CF=O.4 in Pedal Effort Pedal Effort at Pedal Effort at Percent Increase Duo-servo 107.61b 115.2% 50lb Brake Type CF = 0.5 CF = 0.4 in Pedal Effort 50lb 99.81b Two-leading shoe 99.8% 50 1b 107.6 Ib 176.0% 15.2% Duo-servo Leading-trailing 50lb 88.01b 50 Ib 99.8 Ib 99.8% Two-leading Disc brake shoe 50lb 62.51b 25.0% 88.0 1b 76.0% 50 Ib Leading-trailing 25.0% 50 could Ib 62.5 fade. 1b Pedal effort brake 0.1Disc friction-coefficient drop occur from brake more than doubles Brake Type

A with duo-servo drum brakes. Disc brakes have no servo action, so effect of fade is considA 0.1 friction-coefficient drop could occur from brake fade. Pedal effort more than doubles erably less.

with duo-servo drum brakes. Disc brakes have no servo action, so effect of fade is considerably less.

17

I

Cast-iron brake drum is large and heavy compared to disc-brake rotor of equal effectiveness. Many '60s and '70s Cast-iron brake drum is large and Ameriheavy can cars have drums of this This compared to disc-brake rotortype. of equal front-brake drum has'60s integral wheel hub effectiveness. Many and '70s Ameriand can bearings. cars have drums of this type. This

During later days of race-car drum-brake development, a great deal of work was spent cooling-fin design. This type of Duringon later days of race-car drum-brake radial-finned drum pumps air was bedevelopment, a great dealcooling of work tween wheel and drum. spent the on cooling-fin design. This type of

front-brake drum has integral wheel hub Duo-servo and bearings. brakes are most sus-

ceptible to the type of brake fade Duo-servo brakes are most suswhere a force limit is reached. Thus , if ceptible to the brake fade they are ever usedtype in a of racing or highwhere a force limit is reached. Thus, if performance application, care must they are ever used in a racing or highbe taken to use linings that do not performance carewith must have a drastic application, drop in friction inbe takentemperature. to use linings do with not creasing Carsthat fitted have a drastic in friction induo-servo frontdrop brakes have a with tendencreasing temperature. Cars fitted with cy to pull to the right or left if the fricduo-servo front brakes have a tendention in one brake is slightly higher cy to the pullother. to the right or left if the fricthan tion in one slightlyin higher More is saidbrake aboutis linings Chapthan the other. ter 4.

More is said about linings in Chapter 4. BRAKE DRUMS The brake drum is a large, critical

BRAKE brake system. If the drum is part of a DRUMS brake is athe large, critical tooThe small or drum flexible, brake will part of a poorly brake system. If the drum is perform under severe use, no too small flexible, the brake matter howorgood the system may will be. perform severe ause, no Let ' s seepoorly what under constitutes good matter how good the system may be. brake drum. The important properties Let's see what constitutes a good are: brake drum. properties • Must haveThe a important hard wear-resistant are: rubbing surface and the surface finish Must a the hardlining. wear-resistant must not have damage rubbing surface the surface finish • Must be strongand enough to withstand must not damage the lining. the hardest braking, while at high Must be strong enough to withstand temperatures . the hardest braking, while toatdistorhigh • Must be stiff and resistant temperatures. tion and warping. Must bedissipate stiff and heat resistant to distorrapidly and • Must tion and warping. withstand excessive temperatures. Must dissipate rapidlyof grey and Most brake drumsheat are made withstand excessive cast iron, because it temperatures. is hard and wearMost brake are madecarbon, of grey resistant. Castdrums iron contains cast iron, because it is hard and wearwhich prevents galling and seizing resistant. Cast iron contains carbon, when hot. It's also a good d,y rubbing which without preventslubrication. galling and seizing surface when also arigid good dry rubbing Casthot. ironIt's is very , compared to surface without lubrication. most metals. Therefore, the drum reCastdistortion iron is very rigid,load compared to sists under . Because most metals. Therefore, the drum re-, the drum is cast at high temperature sists distortion under load. Because the drum is cast at high temperature, 18

Racers soon discovered that bigger brakes are better. This old Talbot Grand Prix car used wheels-brake drums are Racers18-in. soon discovered that bigger brakes bigger! Fitting into wheel its are better. Thisdrum old Talbot Grandlimits Prix car size. used 1 8-in. wheels- brake drums are

bigger! Fitting drum into wheel limits its size.

it resists warpage when repeatedly heated and cooled. it However, resists warpage whenis repeatedly cast iron not the heated andmetal cooled. strongest in the world; it tends cast iron Tois avoid not this, the to However, crack if overstressed. strongest metal in the world; it tends thick sections are used in a drum . to crack if overstressed. Tostrengthens avoid this, This extra metal not only thickdrum, sections used the in astiffness drum. the but itare increases This extra metal not only strengthens of the drum. It also reduces temperathe but during it increases turedrum, buildup hard the use.stiffness When of thearedrum. also help reduces temperafins used,It they reduce tem'ture buildup duringby hard use. When peratures quickly exposing more fins used, tothey help reduce temmetalare surface the cooling air. When peratures quicklyarebyused, exposing all design tricks a drummore will metal surface to strength. the cooling When have adequate In air. addition, all tricks are used, a drum heatdesign dissipation is improved with will the have adequate strength. In addition, fins and extra metal. heat dissipation is improved with the Drum Cooling-High-performance fins anddrums extra metal. brake must be BIG; bigger the Drum Cooling-High-performance befter is the key for reducing temperathe brake drums must be BIG; tures and eliminating fade. bigger A large the key has for reducing temperabetter is drum diameter the added advantures ofand eliminating fade. A large tage reducing pedal effort because drum diameter has the added advanof the increased "leverage" of the tage of reducing pedal effort friction material-similar to abecause longer of increased "leverage" the pry the bar. Racing drum brakes are of usualfriction material-similar to a longer ly the largest possible diameter that pry bar. Racing brakes are usualwill fit inside thedrum wheel. ly The the largest possible that size and weightdiameter of a brake will fit inside the wheel.in determining drum are important Themuch size heat and energy weightit of brake how can aabsorb. drum are important in determining Brake drums are measured by the how much heat of energy it can inside diameter the drum andabsorb. width Brake drums The are drum measured by surthe of the linings. rubbing inside diameter of the drum and width face is slightly wider than the lining to of the linings. The Don drum allow clearance. ' t rubbing measuresur-a face istoslightly widerlining than width. the lining to drum determine

allow clearance. Don't measure a drum to determine lining width.

radial-finned drum pumps cooling air between the wheel and drum.

Swept Area-The brake-drum inside circumference multiplied by lining Swept inside width isArea-The the brake brake-drum swept area, an imcircumference multiplied by lininga portant measure of how effective width is. the brakea car's sweptbrake area, specifian imbrake is Usually portant measurea ratio of how effective cation includes of brake swepta brake tois. the Usually a car's brake specificar weight. A figure of area cation ratioin.)of brake swept square includes inches a(sq per ton is figurearea of area to Athecarcar weight. typical. with a highAswept square in.) per ton is per ton inches will have(sqlong-wearing, fadecar with a high swept area typical. Abrakes, resistant with all other factors per tonequ will long-wearing, being al. have A typical road carfadehas resistant brakes, with all other about 200 sq in. per ton of sweptfactors area; equal. typical car has may A have twice road this amount. abeing race car about 200 sqdrum-brake in. per ton of swept area; Calculate swept area by athis race car may have twice this amount. formula:

Calculate drum-brake swept area by

Swept area = 3.14 DL in square inches this formula: D = Brake-drum inside diameter in Swept inches area = 3.14 DL in square inches D Brake-drum inside diameter in L = =Lining width in inches inches ToLining calculate area per ton, L= width swept in inches

divide swept area of all four brakes by calculate swept theTo car's weight in tons. area per ton, divide swept area of all four by To help remove heat andbrakes cool the the car's weight in tons. drum, fins are necessary. If the fins Towheel help remove heat and and are designed as acool unitthe to drum, are necessary. If as theanfins promotefins airflow, they can act air and wheel are designed as a unit to pump. Some older race-car drum promote airflow, they can act as an air brakes were highly sophisticated in pump. air Some older race-car drum forcing around the hot parts, as the brakes show. were highly sophisticated in photos forcing air around the hot further parts, as imthe Bimetallic Drums-To photos show. prove cooling, a high heat-conducting Bimetallic Drums-To further immaterial is used outside the cast-iron prove cooling, a highThis heat-conducting rubbing surface. is usually material is used outside the has cast-iron aluminum, although copper been rubbing surface. This is usually tried. Such drums are called bimetaflic. aluminum, although copper Aluminum carries heat from has the been rubtried. Such drums called fins bimetallic. to theare cooling more bing surface Aluminum heat from thebenerubrapidly than carries iron. An additional

bing surface to the cooling fins more rapidly than iron. An additional bene-

Drum

l +

A

Bellmouthing, which results from overheating and hard use, createsBrake angle Shoe A between drum and shoe. This angle causes shoe distortion, extra pedal movement, and faster lining wear on inside edges.

Airflow

Vintage sports car is powered by fuel-injected Chrysler hemi. Because of its high weight and a top speed of over 160 mph, it needed all the brakes it could get. Buick aluminum/cast-iron bimetallic drums were some of the best ever produced for passengercar use.

Bellmouthing, which results from overheating and hard use, creates angle A between drum and shoe. This angle causes shoe distortion, extra pedal movement, and faster lining wear on inside edges.

Airflow Vintage sports car is powered by fuel-injected Chrysler hemi. Because of its high weight and a top speed of over 160 mph, it needed all the brakes it could get. Buick aluminum/cast-iron bimetallic drums were some of the best ever produced for passengercar use.

A

Plate

lron Sheet Steel

.

Cast- lron Drum

Composite Drum Cast Iron

'

Sheet Steel

y

Composite Drum

Aluminum

Cast-Iron Drum

cast 1.0"

Bimetallic Drum

Cast Aluminum

Centrifugally Cast Composite Drum

Of commonly used designs, bimetallic drums cool best due to high heat transfer of aluminum. Bimetallic drums are also the lightest. Bimetallic is lighter. Centrifugally minum around the iron, known as the fit is that aluminum Cast Composite A /-fin process. For an Drum aluminum/iron drum to There Drum are four basic types of brakework properly, the aluminum must be drum construction. The simplest is attached tightly to the iron. The drum Of commonly used designs, bimetallic drums cool best due to high heat transfer of cast in one piece from iron. Another, will not cool sufficiently if there are aluminum. Bimetallic drums are also the lightest. lighter drum style, is the composite air gaps between the two metals. A drum. This type uses a sheet-steel once-popular type of bimetallic drum aluminum is lighter. fitused is that around therim iron, the h u b with an iron castknown to it. Aasvariaa special process for casting alu- minum

For an aluminumliron drum to work properly, the aluminum must be attached tightly to the iron . The drum will not cool sufficiently if there are air gaps between the two metals. A once-popular type of bimetallic drum used a special process for casting alu-

A I-fin process. There are four basic types of brakedrum construction. The simplest is cast in one piece from iron. Another, lighter drum style, is the composite drum. This type uses a sheet-steel hub with an iron rim cast to it. A varia-

Wheel Rim

Angled lip on drum can help cooling. If lip has fins, drum rotation can pump air between the wheel and drum. If lip extends inboard past wheel and backing plate, additional cooling is realized.

tion of the composite drum uses a stamped sheet-steel drum with a castAngled lip on drum can inside help cooling. lipa iron rubbing surface it. LastIf is has fins, drum rotation can pump air bebimetallic drum, made of aluminum tween the wheel and drum. If lip extends inand cast board pastiron. wheel and backing plate, addiDrum Design-The tional cooling is realized. design of the open edge of the brake drum is critical tion of the performance. composite drum uses a to a drum's The stiffness stamped sheet-steel drumwill withkeep a castof the lip at the edge the rubbing it. Last (egg is a iron drum from surface going inside out-of-round bimetallic , made of aluminum bellmouthing (diameter inshaped) ordrum and cast iron creasing at . open end) under severe Drum Design-The design of Also, the loads and high temperatures. open edge ofofthethe brake is critical the shape lip drum can determine tohow a drum's stiffness well aperformance. drum cools. The An angled lip of lip promote at the edge will around keep the canthehelp airflow the drum going out-oj-round (egg drum.from Because airflow around a drum shaped) or bel/mouthing (diameter inis complicated and affected by other creasing at open end) under severe parts on the car, drum cooling can loads and high temperatures. Also, only be determined by tests. the Besides shape of the lip and can cooling determine stiffening the how wellthe a lip drum lip drum, alsocools. matesAn withangled the backcan airflow around ing help plate.promote This helps keep dirt the and drum. around a drum water Because out of airflow the drum. The usual isdesign complicated and affected by other has a groove at the edge of the parts the car, brakeondrum. T h e drum outer cooling edge ofcan the only be determined by tests. Besides stiffening and cooling the drum , the lip also mates with the backing plate. This helps keep dirt and water out of the drum. The usual design has a groove at the edge of the brake drum . The outer edge of the

19

Fins on Alfa-Romeo aluminum/cast-iron drum are designed to pump air between drum and Alfa-Romeo tight-fitting aluminum/cast-iron wheel. Drum goes Fins on with brake assemblyto pictured on page 22. drum are designed pump air between Photo and by Ron Sessions. wheel. Drum goes drum tight-fitting with brake assembly pictured on page 22. Photo by Ron Sessions.

backing plate is flanged. This flange fits into the groove, but does not backing is This flanged. Thisfor flange touch theplate drum. is a seal dirt fits water, into the groove, but does not and making it difficult for fortouch the drum. This is a seal for dirt eign matter to blow or splash into the and water, it difficult for fordrum. The making brake-lining surfaces are eign to from blow contamination. or splash into the thus matter protected A drum. are problemThe withbrake-lining this seal is surfaces it also prethus protected contamination. A vents cooling from air from entering the problem with this seal is i t also preinterior of the brake.

vents cooling air from entering the

interior of the brake. BACKING PLATE The backing plate is a bracket on BACKING which the PLATE brake shoes and wheel The backing is serves a bracket on cylinders mount.plate It also to prowhich brake ofshoes and wheel tect thetheinterior the drum from cylinders mount. as It also serves to procontamination, just discussed. tect the interior of the drum from Braking torque is transmitted from contamination, as just discussed. the shoes to the suspension of the car Braking is transmitted from through torque the backing plate. A good the shoes to the suspension of the car backing plate must be stiff and strong through the backing plate. A good so the shoes stay in alignment with backing plate musta be stiff and strong the drum. When backing plate deso the excessively shoes stay inunder alignment flects load, with the the drum. driver feels When this asa abacking spongy plate pedaldeor flects excessively under load, the as excessive pedal travel. driver this asplates a spongy pedal or Mostfeels backing are stamped as excessive pedal travel. from heavy sheet steel. Ridges, Most and backing plates are stamped bumps edge lip stamped into the from heavy sheet steel. Ridges, backing plate increase its strength and bumps andCritical edge lipareas stamped into the stiffness. for strength backing increase its strength and are the plate brake-shoe-pivot and wheelstiffness. Critical areas for strength cylinder mounting points. Any cracks areother the brake-shoe-pivot wheelor weakness in thoseand areas can cylinder mountingsituation. points. Any cracks cause a dangerous or Some other backing weaknessplates in those areas race can on older cause a dangerous situation. cars are cast aluminum or magnesium backingThese plates are on older race forSome lightness. not good cars are cast or magnesium materials for aluminum this application because for These are not good they lightness. lack sufficient stiffness and materials for this application because strength. By the time an aluminum or they lack sufficient stiffness and strength. By the time an aluminum or

20

Early race-car drum brake has finned backing plate to help cooling. Unfortunately, the designer neglected usehas vents. And, beEarly race-car drum to brake finned backcause thetobacking plate Unfortunately, doesn't get very ing plate help cooling. the hot, theseneglected cooling fins help much. designer to don't use vents. And, because the backing plate doesn't get very hot, these cooling fins don't help much.

magnesium casting is sufficiently beefed up to equal the strength of a magnesium castingit will is be sufficiently steel backing plate, nearly as beefed up to equal the strength of a heavy. steel plate, it will nearly as Thebacking backing plate is be a precision heavy. part. Brake-shoe mounting points Thebebacking is brake a precision must aligned plate with the drum part.proper Brake-shoe points for operation.mounting A bent or twisted must be aligned the brake drum backing plate is with useless, so inspect for proper operation. A bent or twisted each one carefully for damage when backing plate is useless, so inspect working on your car. You should each one for damage when never pry carefully on a backing plate to working a on your car.This Youwillshould remove brake drum. bend neverbacking pry onplate a backing plate the to the and misalign remove a brake drum. This will bend brake shoes. theA backing plate isand misalign backing plate usually boltedthe to shoes. upright or axle flange abrake suspension A backing plate high-strength is usually bolted to with tight-fitting, bolts. aIt suspension upright or axle flange is important that this joint is tight with tight-fitting, and cannot shift high-strength under load. bolts. This It is important that this joint tight brings up an important point. isWhen and cannot working on shift brakes,under makeload. sure This the brings up an important point. bolts are the correct lengthWhen and working for on the brakes, make sure the strength application. bolts are theCooling-The correct length and Drum-Brake backing strength for the application. plate has little brake-cooling effect. It Drum-Brake never gets as Cooling-The hot as the otherbacking brake plate has little brake-cooling It parts. Therefore, fins or air effect. blowing never as hot other brake on the gets backing plateasisthe ineffective. Efparts. to Therefore, fins orbrake air blowing forts cool a drum should on the backing plate is ineffective. Efalways be directed to the drum. forts to backing cool a drum brake should Some plates are vented or always be directed to theon drum. have scoops mounted them. The Some backing plates are vented or purpose is to direct cooling air into have scoops mounted on them. The the interior of the brake drum. This purpose is to direct cooling into setup is found on most drumair brakes the interior of the brake drum. This used for racing, if the rules allow it. setupproblem is found with on most drumbacking brakes The ventilated used for racing, if the rules allow it.

The problem with ventilated backing

Large forward-facing scoop was used on 520-HP Auto Union Grand Prix cars from the mid-'30s. These cars usedwas huge drums Large forward-facing scoop used on and butPrix brake cooling 5 2 0 -hydraulic H P Auto actuation, Union Grand cars from withmid-'30s. that muchThese powercars was used a realhuge problem. the drums and hydraulic actuation, but brake cooling with that much power was a real problem.

Although most brake shoes are made of steel plate, cast aluminum has been used. Aluminum most is lighter, weakens at exAlthough brakebut shoes are made of treme temperatures. If youhas arebeen building a steel plate, cast aluminum used. car with aluminum make sure Aluminum is lighter,shoes, but weakens at they exwon't temperatures. be subjected Iftoyouextremely high treme are building a temperatures. Never use metallic racingcar with aluminum shoes, make sure they brake linings on aluminum won't be subjected to shoes. extremely high temperatures. Never use metallic racingbrake linings on aluminum shoes.

plates is that the venting may allow entry of water, dirt or other plates is that the venting maybraking allow contamination. This creates entry of particularly water, dirt or side other problems, if one of contamination. This more createsthan braking the car is affected the problems, particularly if one sideside of other. Grabbing or pulling to the the car is affected more than the while braking can result. other. Grabbing to the side A scoop shouldorbepulling designed to keep while braking can result. out contamination. To do this, some A scoop should be designed to keep people place a screen flush with the out contamination. To do this, some scoop intake. This restricts airflow to people place a screen flush the the brake, thus defeating the with purpose scoop intake. AThis to of the scoop. goodrestricts solutionairflow is to use the brake, thus defeating the purpose a long air duct with a coarse screen re-

of the scoop. A good solution is to use a long air duct with a coarse screen re-

Adjuster Cab le

Hold -

Return springs and hold-downs have been removed from these brake shoes. Springloaded hold-downs the shoes against Return springs and keep hold-downs have been flats on the backing shoeSpringedges removed from these plate. brakeThe shoes. rub against these flats asthe they moveagainst in and loaded hold-downs keep shoes out. on the backing plate. The shoe edges flats rub against they Thus move ,inonly and cessed intothese the flats duct asinlet. out.

Adjuster Levers

ｾ＠

1 .,-)

fine partic les are likely to reach the

cessed ductwill inlet. Thus, only brake . into The the screen tend to repel fine particles are likely to reach the stones and other large objects entering brake. Thebut screen tendairflow to repel the duct, won'twill block as stones other large objectsthat entering much . and However, be aware dust the but brake won't and block as will duct, enter the mayairflow increase much. However, be aware that dust lining wear and drum-surface scoring. will enter the brake and may increase lining wear and drum-surface scoring. BRAKE SHOES Brake shoes are rigid metal assem-

BRAKE blies to SHOES which friction material is Brake shoes are rigid metalorassemattached. Friction material, brake blies material is lining, tois which ri veted friction or bonded to the brake attached. Friction material, or brake shoe. Brake shoes are usually or basis bonded to can the lining, sold on isan riveted exchange so they brake shoe.by Brake shoes usually be rebuilt installing newarelining on sold on an exchange so they the old shoes. Brakebasis shoes can can be be rebuiltandby used installing new lining on repeatedly unless relined the Brake shoes can be they old haveshoes. been damaged. relined and used unless Most brake shoesrepeatedly are fabricated of they have been damaged. sheet steel with a tee-shaped cross Most brake fabricated of section. Someshoes are are made of cast sheet steel. The with shoe a tee-shaped cross is shaped to aluminum section. Some made ofof cast match the insidearediameter the aluminum. shoe is shaped to drum , with The new full-thickness lining match the inside diameter of the installed . Accurate fit between the drum, and withdrum newisfull-thickness lining lining assured by machininstalled. Accurate fit between the ing the lining after it is attached to the lining This and drum is assured by machinshoe. machining process is called it is exact attached to the ing thethe lining afterThe lining. radius of arcing shoe. This machining process is called the arc is determined by the inside arcing the lining. TheIfexact radiushas of radius of the drum. the drum the arc is determined by the inside been turned to an oversize diameter, drum has radius of the drum. the lining-arc radius Ifis the increased to been turned to an oversize diameter, match. theBrake lining-arc increased to shoes radius have is rubbing points match. that are contacted by wheel-cylinder Brake shoesand havebrake rubbing points mechanisms adjusters. that are contacted by wheel-cylinder Also, there's a mechanical linkage mechanisms andparking brakebrake adjusters. connected to the , which Also, there's a mechanical operates the rear brake shoes. linkage These connected to the which rubbing points areparking subjectbrake, to wear and operates the rear brake shoes. These rubbing points are subject to wear and

Adjusting-Hole Cover

ｾ

Adjusting-Screw Spring

ｾ＠

Adjust in g-Screw Assemb ly

Assembly in the typical drum brake. This is a duo-servo rear brake Various types of springs are usedAdjusting-Screw with an automatic adjuster. Drawing courtesy Bendix Corp. Various types of springs are used in the typical drum brake. This is a duo-servo rear brake with an automatic adjuster. should be lubricated withDrawing specialcourtesy high- Bendix Corp.

temperature grease for maximum life .

should lubricated with special highBrakebeshoes have holes in them for temperature grease for maximum life. locating pins and return springs. Brakebuying shoes new have shoes, holes inmake themsure for When locating pins and ones return springs. the holes in the new match those. When new shoes, in the buying old shoes. Shoes make often sure get the holes in the new ones match those., mixed up when relining is performed in carefully the old comparing shoes. Shoes so old ofter! to newget is mixed up when relining is performed, worthwhile. When installing the new so carefully oldwhere to newthe is shoes, pay comparing attention to worthwhile. When installing the new return springs connect. Some shoes shoes, pay attention the have extra holes toforwhere various return springs applications. If aconnect. spring isSome placedshoes in a have hole, extra poor holes various wrong brake for performance applications. a spring is grabbing placed inora can result, in Ifthe form of wrong hole, poor brake performance dragging brakes. canBrake result, in grabbing or shoesthe getform very ofhot in racing dragging brakes. use, but not nearly as hot as the drum . Brake shoes hot the in racing If the shoe gets get too very hot and lining use, butworking, not nearly as hotofasthe the liningdrum. is still failure If the shoe gets toocould hot and the lining to-shoe bonding occur. Foris still working, failure of the tunately, most heat generatedliningby a to-shoebrake bonding occur. drum goes tocould the drum andFornot tunately, heat generated the shoes,most so overheated shoesbyarea drumBrakes brake goes theed drum and linnot rare. using to bond metallic the shoes, so overheated shoes are ings are the type for which bonding rare. Brakes using bonded metallic linstrength is extremely important. ings are the type design for which bonding Lining-material is more imstrength is extremely important. portant than brake-shoe design . See Lining-material design is discussion more imChapter 4 for an in-depth portant than brake-shoe design. See of brake linings. Chapter for anshoes in-depth discussion Usually4, brake are held to the of brake linings. Usually, brake shoes are held to the

Girlock of Australia manufactures this lightweight mechanically-operated brake for use asofa parking brake on '84-and-later Girlock Australia manufactures this Chevrolet It has all the features lightweightCorvettes. mechanically-operated brake of standard drum brake, including an adforause as a parking brake on '84-and-later juster and Corvettes. return springs. in Chevrolet It hasDrum all theinstalls features the hat. including Photo courtesy of a disc-brake-rotor standard drum brake, an adGirlockand Ltd.return springs. Drum installs in juster the disc-brake-rotor hat. Photo courtesy backing plate with a spring clip or Girlock Ltd.

spring-loaded pin. This pin lightly backing platebrake with shoe a spring clip the or presses the against spring-loaded pin. This pin lightly backing plate. Flats are provided on presses brakeforshoe against the the backithe ng plate the edge of the backing plate.against. Flats are provided on shoe to rest Pressure of the the backing plate for the edge of the shoe hold-down springs is low, so fricshoe rest against. Pressure of the tion isto minimal.

shoe hold-down springs is low, so friction is minimal. RETURN SPRINGS Drum-brake shoes are pulled away

RETURN SPRINGS Drum-brake shoes are pulled away 21

Brake adjuster is operated by turning star wheels. This type adjuster is used between the on byaturning leadingBrake brake adjuster shoes is operated star and-trailingdrum brake. Adjuster wheels. This shoe type adjuster is used between housing is mounted to backing plate.leadingthe brake shoes on a

and-trailing-shoe drum brake. Adjuster housing is mounted to backing plate.

from the drum-retracted-after application by a set of return springs. Befrom the apcause the drum-retracted-after force exerted by these plicationisbyhigh, a set of return springs. springs a special tool is Berecause to theinstall forcethem. exerted quired Thereby are these varisprings is high, a and special tool for is the reous arrangements mounts quired install them. There are return tosprings, depending on varithe ous arrangements and mounts for the specific design. return on thea If the springs, brake hasdepending any servo action, specific design. loss of return-spring force can cause the brake hasorany theIf brake to lock grabservo . Thisaction, may bea lossdangerous of return-spring can cause as as a lossforce of braking. For the brake if to only lock or grab. Thisloses may be instance, one wheel its as dangerous as a loss of side braking. For return-spring force , that can lock instance, if only one swerve wheel or loses a sudden skidits . up and cause return-spring force, that side can lock Some manufacturers provide difup and return cause a springs sudden swerve or skid. ferent that give a difSome manufacturers provide different force when installed. Springs ferent return springs by thatcolor. give Check a difare usually identified ferent force when installed. Springs with your parts supplier to be sure you are usually identified by color. Check have the correct ones on your vehicle. with your parts supplier to be if sure This is particularly important theyou car have the correct ones on yourorvehicle. is fitted with heavy-duty racing This is particularly important if the car brakes.

is fitted with heavy-duty or racing brakes. BRAKE ADJUSTERS

The return springs pull the brake BRAKE ADJUSTERS shoes away from the drum a minimum The return springs pulldistance the brake specified distance . If the the shoes away from the drum a minimum shoes must travel before contacting specified If theexcess distance the the drum distance. is too great, brakeshoes must results. travel before pedal travel Thus , contacting some adthe drum must is toobegreat, excessto brakejustment provided minipedal travel results. Thus, admize shoe clearance and to some compenjustment mustwear. be provided to minisate for lining mize shoeare clearance and to of compenThere two types brake sate for lining wear. adjusters, ma nua I and a uloma lie. There are two and types automaticof brake Both manualadjusters,designs man~/aland adjuster use aautomatic. cam or screw-

Both manual- and automaticadjuster designs use a cam or screw-

22

Prior to disc brakes, some drum-brake designs got pretty exotic. This three-leading-shoe drum brake was used on some Alfa Romeo sports cars. Although they did a good job of stopping the little sports cars, they weredesigns heavy and Notice that each shoe has its Prior to disc brakes, some drum-brake got complex. pretty exotic. This three-leading-shoe own drumwheel brakecylinder. was used on some Alfa Romeo sports cars. Although they did a good job of

stopping the little sports cars, they were heavy and complex. Notice that each shoe has its own wheel cylinder.

thread mechanism to move the brake shoes toward or away from the drum. thread mechanism move the brakea The duo-servo tobrake uses shoes toward or away from the drum. turnbuckle-like threaded link between The duo-servo brake uses the primary and secondary shoes.a turnbuckle-like threaded link between There are right-hand threads on one the primary and secondary shoes. end and left-hand threads on the There are right-hand threads on other. A star-shaped wheel, whichone is end and left-hand on thea rotated manually withthreads a tool through star-shaped wheel, is other. hole inA the brake drum or which backing rotated manually with a tool through plate, turns the threaded link. This ro-a hole the brake or backing tation in makes the drum link shorter or plate, the threaded link. This rolonger,turns increasing or decreasing shoetation makes the link shorter or to-drum clearance. longer, increasing or decreasing shoeAutomatic adjusters have a linkage to-drum clearance. that rotates the star wheel as the vehihave a linkage cleAutomatic is backedadjusters up and brakes are that rotates the star wheel as the vehiapplied. This is a ratchet-type cle is backed only up and brakes are mechanism-it works in one applied. . Automatic This is adjusters a ratchet-type direction are not mechanism-it only worksThere in one actuated in forward driving. is a direction. Automatic adjusters are not limit to the stroke of the actuating in forward driving. There the is a actuated linkage. When clearance between limit and to the of the actuating shoe the stroke drum reaches a certain linkage.the When clearance between the value, actuating linkage jumps shoe and the drum reaches a certain over the next tooth on the star wheel. value,feature the actuating jumps That prevents linkage the automatic over the next tooth on the star wheel. adjusters from overtightening the That brakes.feature prevents the automatic adjusters from overtightening thea Other types of brake adjusters use brakes. cam or an eccentric bolt for adjusting

Other types of brake adjusters use a cam or an eccentric bolt for adjusting

the shoes. These are actuated manually by turning a bolt that protrudes the shoes.the These are actuated manualthrough backing plate or by using ly by turning a bolt that protrudes a screwdriver through a hole in the through the backing plate or by using brake drum. a screwdriver throughisa covered hole in the Adjusting brakes in brake drum. Chapter 11 .

Adjusting brakes is covered in Chapter 1. WHEEL1CYLINDERS Brakes are applied by hydraulic WHEEL CYLINDERS fluid inside wheel cylinders. One or two Brakesin are pistons eachapplied cylinderbyarehydraulic moved fluid inside cylinders. One orwhen two outward by wheel brake-fluid pressure pistons in each cylinder are moved the driver pushes on the brake pedal. outward by brake-fluid pressure when Piston movement is transmitted to the pushes onthe thebrake brakeshoe pedal. the driver movable end of by movement is transmitted to aPiston pushrod or other linkage. theThere movable of the brakeofshoe by are end many types wheel acylinders. pushrod or other linkage. Cylinders are made from There are types are of singlewheel aluminum or many iron. There cylinders. Cylinders are made from or dual-piston cylinders, depending aluminum or iron. Duo-servo There are singleon brake design. brakes or cylinders, depending havedual-piston one cylinder operating two on brake brakes shoestwodesign. pistons Duo-servo are used with this have cylinder operating design. one Others have one cylinder two on shoes-two pistons are used with this each shoe-one-piston cylinders are design. used. Others have one cylinder on each shoe-one-piston cylinders are Wheel cylinders and other hydraulic used. components are discussed in more Wheel cylinders5. and other hydraulic detail in Chapter

components are discussed in more detail in Chapter 5.

Disc Brakes

3

Racing-brake setup on this March Indy Car uses four-wheel disc brakes with dual master cylinders pressurized by remotely adjustable balance bar. Brake cooling is critical at Phoenix International's one-mile oval. Photo by Tom Monroe.

Racing-brake setup on this March lndy Car uses four-wheel disc brakes with dual master cylinders pressurized by remotely adjustable balance bar. Brake cooling is critical at Phoenix International's one-mile oval. Photo by Tom Monroe.

Rotor

Caliper

Shield

Transfer Tube

Splash Shield

Major parts of disc brake are caliper, rotor and splash shield. A transfer tube connects hydraulic cylinders on opposite sides of Major parts of disc brake are caliper, rotor this fixed caliper. othertube fixedconnects calipers and splash shield. Many A transfer have internal fluid passages. Photosides courtehydraulic cylinders on opposite of sy Bendix Corp. Many other fixed calipers this fixed caliper.

have internal fluid passages. Photo courtesy Bendix Corp.

Disc brakes are used on the front of most modern road cars, and on all Disc brakesofaremost usedrace on the front of four wheels cars. Disc most modern road cars, and on all brakes were first introduced on cars in four wheels race cars. the late '40s. ofBymost the early '70s, Disc disc brakes first introduced on carson in brakes were had replaced drum brakes the late '40s. By the early '70s, disc the front. brakes had replaced brakes on typesdrum of disc brakes Two common the front. are single and multiple disc, both with Two common of disc brakes discs or types rotors. Single-disc rotating are single and multiple disc, both with types have a rotor, which is clamped rotating discs or rotors. Single-disc on by friction material called brake types Multiple-disc have a rotor, which clamped pads. types, is commonly brake on byonfriction used aircraft,material have acalled number of Multiple-disc types, commonly pads. rotating discs separated by stators, or used on aircraft, have a number stationary discs. Operation is by ofa stators, or rotating discs separated by large-diameter hydraulic piston in the stationary discs. Operation by a backing plate moving outward,isclamplarge-diameter piston in the ing the rotors hydraulic and stators together. backing plate moving outward, clampMultiple-disc brakes are 100% ing the , rotors stators types together. metallic while and single-disc use Multiple-disc brakes are 1000/o organic/metallic friction material.

metallic, while single-disc types use organic/metallic friction material.

ADVANTAGES OF DISC BRAKES The auto industry changed from ADVANTAGES DISC BRAKES drum brakes toOF disc brakes for a The auto industry changed from number of reasons: drum brakes to disc brakes for a • More resistant to brake fade. number reasons: • Better of cooling. More resistant to brake fade. and dirt resistant. • Water Better cooling. • Less maintenance. Water andsurface dirt resistant. • Greater area for a given Less of maintenance. weight brake. Greater surface area for given The main advantage disc a brakes weight of brake. have over drum brakes is their inThe main advantage disc reasons brakes creased resistance to fade . The havethisover for are : drum brakes is their increased resistance to fade. Theexposed reasons • Friction surfaces directly for this are: to cooling air. surfacesis directly exposed • Friction Drum deflection eliminated. to cooling air. have no servo action. • Disc brakes Drum deflection eliminated. The lack of servoisaction is a disadDisc brakes have no action. vantage with a heavy servo car. Resulting The lack of servo action is disadpedal effort is too high. As aa result, vantage with almost a heavyalways car. Resulting brakes require disc pedal effort is too high. As a result,

disc brakes almost always require

23

AHeatlnput

Air Cooling

Heat Input

" I_\J" ｾ＠

Drum

Drum

Heat lnput Drum Brake

Drum Brake

Rotor Disc Brake

Rotor

Why a disc brake has superior cooling is illustrated here. Heat generated by brake drum Disc Brake must flow through drum before air can cool the brake. On a disc brake, hot rubbing surfaces are directly exposed to cooling air; heat-to-air transfer begins immediately Why a disc brake has superior cooling is illustrated here. Heat generated by upon brakebrake drum application. must flow through drum before air can cool the brake. On a disc brake, hot rubbing surfaces

are directly exposed t o cooling air; heat-to-air transfer begins immediately upon brake application. Expansion

Adapted to a hot rod, early Chrysler Imperial disc brake looks like a drum brake and works like Adapted toaaclutch. hor rod,Although early ~ nneat r y s llooking, e Imper it worklooks as well a modern rialdoesn't disc brake like as a drum brakedisc and brake. like Rubbing surfaces on brake are on works a clutch. Although neat looking, inside of finned i t doesn't work housing. as well as a modern disc

brake. Rubbing surfaces on brake are on inside of finned housing.

Direction

Expansion Direction

Expansion Direction

Expansion Direction Pad

Drum

Drum

_

d$$ ... -..._. .. . _ . ..__-_.... , . Drum Brake

&pad ... ..,.. 8 .

... ..I

Shoe

Drum Brake

Rotor

Disc Brake

Disc Expansion of hot brake drum is away from brake shoes. This requires extra pedal travel. A Brake disc-brake rotor expands slightly toward the pads. Therefore, extra pedal travel due to heat expansion is brake not a problem hot disc brake. Expansion of hot drum is with awaya from brake shoes. This requires extra pedal travel. A

disc-brake rotor expands slightly toward the pads. Therefore, extra pedal travel due to heat expansion is not a problem with a hot disc brake.

SPOT BRAKES & -, DISC BRAKES SPOT BRAKE9 & first called a The disc brake was

Disc brakes were used on many race cars in the mid-'50s. This car, built in 1955, is powered by were a 300-HP Chevy. Disc brakes used on many Tiny race solid cars rotors would never becar, used today on such is in the mid-'50s. This built in 1955, a powerfulby car.a 300-HP Chevy. Tiny solid powered

rotors would never be used today on such assist, apower powerful car. while drum brakes with

high servo action may not. On race power assist, while drumless, brakes cars , weight is much so with disc high servo action may not. On race brakes usually do not require power cars, weight is much less, so disc assist. brakes usually part do not The hottest of arequire brake power is the assist. metal surface contacted by the friction The hottest a brake the On a part drumofbrake, thisis surmaterial. metal surface contacted by the friction face is inside the drum; on a disc material. Onthe a drum brake, thisrotor. surexterior of the brake, it is face is inside the drum; on a disc For a drum brake to cool, the tembrake, it is the exterior of the rotor. perature of the entire drum must first For aThen drumthebrake theattemdrumto iscool, cooled the rise.

perature of the entire drum must first rise. Then the drum is cooled at the 24

DISC BRAKES spot brake or spot disc brake. The dlsc brake was first acalled a This distinguished it from type of spot brake brake that or spot brake. disc has adisc clutch-like a type of This dlstlnguished full circle of frictionIt from material. This disc brake thatof has ctufcblike unusual type disca brake was full of frlction material. This Chrysler Imperial in usedcircle on the unusual was the early type '50s, of butdisc was brake discOritintheofChryder Imperial in used ued i'non favor the traditional drum the early '50s, but was discolltln-brake. ued In favor ofmultidisc the traditional Full-circle brakesdrum are brake. Full-circle multidisc brakes are

exterior by surrounding air. A disc brake is cooled immediately by air exterior A disc the disc'sair. rubbing blowing byonsurrounding brake is cooled immediately by air surfaces. blowing on the disc's rubbing drum expands-ID A brake surfaces. increases-when it gets hot, increasbrake expands-ID ingA pedal travel.drum The drum can also increases-when it gets warp from temperature hot, or increasbraking ing travel. The deflection drum can also deforce.pedalBrake-drum warp temperature or braking creasesfrom performance and causes fade. force. Brake-drum derotor is essenHowever, a disc-brake deflection creases performance and causes fade. tially a flat plate. Temperature expanHowever, disc-brake rotortheisfriction essension of thearotor is toward

tially a flat plate. Temperature expansion of the rotor is toward the friction

used on large aircraft. Light aircraft typically use more conventional used on large Light alrcraft spot-type discaircraft. brakes. There's a typlcelb use more convent~onal brief discussion of aircraft brakes spot-type disc brakes. There's a in Chapter 9. brief discussion aircraft brakes To keep things of simple, I call the in Chapter automotive 9. standard disc ', brake -simply To keep th'inggsimple, I call the a disc brake because the standard brake brake is nodisc longer in term spot automotive simply a use. disc And, brake I beaause the common call aircraft term spotbrakes brake simply Is no longer in multidisc multidisc cbrakes. m m n use. And, I oall aircraft

multidisc brakes simply multidiso brakes.

material rather than away from it. Squeezing a disc cannot cause suffimaterial rather tothan from it. cient deflection affectaway performance. Squeezing a disc cannot cause The lack of servo action meanssuffithat cient deflection performance. a disc brake to is affect affected little by The lack servo action that changes in of friction. As I means mentioned aearlier, disc drum brake brakes is affected little by with maximum changes in friction. As I mentioned servo action are also affected the most earlier, drum brakes maximum by friction changes. Awith slight drop in servo action most friction, suchare as also thataffected caused the by heat, by friction changes. A slight drop in is magnified by the servo action . The friction, such as that caused by heat, driver senses this as fade. Disc brakes is magnified by the servo action. The as sensitive as drum are simply not

driver senses this as fade. Disc brakes are simply not as sensitive as drum

JFZ disc brake is designed to stop a oval-track race car. Four-piston, I lightweight caliper is is massive to reduce JFZ disc brake designed to stopde-a flections minimize temperature. Photo powerful and oval-track race car. Four-piston, courtesy JFZ Engineered Products. lightweight caliper is massive to reduce de-

Changing brake pads on most disc brakes is easy. Pads are sometimes retained with quick-release pins. New being inChanging brake pads on pads mostare disc brakes stalled thisare transaxle-mounted caliper is easy. in Pads sometimes retained with for bedding in. pins. New pads are being inquick-release

flections and minimize temperature. Photo courtesy JFZ Engineered Products.

stalled in this transaxle-mounted caliper for bedding in.

Ipowerful

Rotor bolts to lightweight aluminum hat. Assembly then bolts to wheel hub or axle . . Deep flexes when rotor aluminum expands from Rotor hat bolts to lightweight hat. high temperature and to minimizes brake heat Assembly then bolts wheel hub or axle. transferred to thewhen wheelrotor hub expands and bearings. Deep hat flexes from Photo courtesy JFZ Engineered high temperature and minimizesProducts. brake heat

transferred to the wheel hub and bearings. Photo courtesy JFZ Engineered Products.

brakes to changes in friction. The shape of a drum brake also conbrakes in friction. tributestotochanges fade. Many organic brake The shape of a drum con-. linings expel gases brake when also heated tributesgases to fade. Many brake These can act as aorganic lubricant belinings expel when causing heated. tween the lininggases and drum, These as a lubricant befrictiongases loss can andact severe brake fade. tween the lining and drum, causing The cylindrical surface of a brake friction and severe brake infade. drum is loss similar to bearings an The cylindrical surfacehigh-pressure of a brake engine. For example, drum is similar bearings in an oil between a main tobearing and crankengine. For example, high-pressure shaft journal keeps the surfaces apart oil between bearing and and friction atomain a minimum. A crankbrake shaft journal keeps the surfaces drum and shoes act much like an apart oiled and friction to a minimum. A gas brake bearing and journal when hot is drum and shoes act much an oiled expelled between them.like They are bearing when hot gas is pushed and apartjournal by the high-pressure expelled between them.andThey are gas , reducing friction causing pushed apart by the high-pressure brake fade. gas, frictionarea andof causing Thereducing small surface a discbrake brake fade. pad and the flat face of the rotor surface area of a discdoThe not small simulate a bearing container. brake pad and the flat face of the There may be some gas coming rotor from do simulate a bearing the not lining, but because it iscontainer. not conThere someisgas coming tained may well,bethere little effect.from To the lining, it is on nota conrepeat, any but dropbecause in friction disc tained well, there littleon effect. To it lessis than a drum brake affects repeat, any drop in friction on a disc brake because the disc brake has no brake action affects. it less than on a drum servo brake because cooling the discisbrake no Disc-brake betterhasthan servo action. drum-brake cooling because the rotorDisc-brake cooling is better than contact surfaces are directly exposed drum-brake cooling becausethis themakes rotorto cooling air. However, contact surfaces are directly exposed the contact surfaces "potentially" to cooling air. However, this makes more vulnerable to damage from corthe contact surfaces "potentially" rosive dirt or water contamination. more vulnerable corFortunately, theto damage constantfrom wiping

rosive dirt or water contamination. Fortunately, the constant wiping

action of the pads against the rotor keeps the surfaces clean. Also, cenaction the tends pads to against rotor trifugal of force throwthe material keeps the surfaces clean. Also, cenoff the rotor. Because water is wiped trifugaltheforce tends throw material from rotor, discto brakes are less off the rotor. Because water is wiped sensitive to this contamination than from the rotor, disc brakes less drum brakes. On the otherarehand, sensitive to this contamination than water lubricates a drum brake well. drum more brakes. On action the other And, servo meanshand, less water lubricates a drum brake well. braking. And, more servo action less Disc-brake pads are easymeans to change braking. on most cars. Usually, disc pads can padsremoving are easy the to change beDisc-brake changed after wheel on most cars.locking Usually, disc Some pads 'can and a simple device. inbe changed after removing the wheel stallations requires removing the and a simple locking device. Some incaliper. stallations requires removing the Another advantage of disc brakes caliper.drums is adjustment. Drum over Another of disc brakes brakes mustadvantage be manually adjusted or over drums is adjustment. must have the added complexityDrum of an brakes must be manually adjusted or automatic-adjusting system . Disc must added to complexity an brakeshave are the designed run with of little automatic-adjusting system. each Disc clearance, and are self-adjusting brakes are designed to run with little time they are applied . clearance, and are rotor self-adjusting each The disc-brake has a contact time they are applied. surface on each side; the brake drum rotor has contact hasThe a disc-brake contact surface onlya on the surface on each side; thearea brake drum inside. Disc-brake swept is larger has contact surface only brake on the whena compared to a drum of inside. Disc-brake swept area is the same diameter and weight. larger More when compared a drum brake of swept area means to better cooling.

the same diameter and weight. More swept area & means better cooling. ROTORS HATS

The rotor, usually made of cast ROTORS HATSand heaviest part of iron, is the&largest The rotor, of disc cast a disc brake. Itusually is a flatmade circular iron, is the largest and heaviest part of with a contact surface on each side.

a disc brake. It is a flat circular disc with a contact surface on each side.

The rotor may either be solid or it can be vented with cooling passages The rotorit.may either be solid or i t can through be vented with iscooling passages HatsThe rotor usually attached through to a hat, it. which in turn is attached to a Hats-The rotor is flange. usually The attached wheel hub or axle hat to a hat, which in turn is attached to a gives a long path for heat to travel wheelthe hub or rubbing axle flange. The hat from brake surface to the gives long pathThis for heat travel wheel a bearings. keepsto wheelfrom thetemperature brake rubbingdown. surface to the bearing The hat wheel bearings. This keeps wheelsometimes is cast integral with the bearing temperature hat rotor, and sometimes down. it is a The separate sometimes is cast integral with the part. rotor, it is aorseparate Hatsand are sometimes made of iron lighter part. material, such as aluminum. ProHats are hats madeareof usually iron oriron lighter duction-car and material, such aluminum. Prointegral with the as rotor. Most race-car duction-car hats are iron and hats are separate and usually made of alumiintegral with the rotor. Most race-car num alloy. hats are non-integral separate and rotors, made ofthe alumiWith hatnum alloy.attachment can be either of to-rotor With rotors, the hattwo typesnon-integral , bolted or dog-drive. A dogto-rotor attachment can be either of drive is a series of radial slots in the two types, bolted or dog-drive. A dogrotor with metal driving dogs attached drive seriesact of asradial slots the to the is hat.a They a spline to in transrotor with metal driving dogs and attached mit torque between brake hat. to the hat. actthe as arotor splinetotoexpand transThese dogsThey allow mit torque between brake and hat. freely while keeping the rotor cenThese dogsthe allow rotorfreedom to expand tered on hat.theThis to freely keeping cenexpand while eliminates loadsthe therotor hat would tered on get thewhen hat. the This freedom otherwise rotor gets hot.to expand loadstothe would If the eliminates hat is bolted thehat rotor, it otherwise get when the rotor rotor gets must expand with the as it hot. gets If the hathat is bolted to the thin rotor,andi t hot. If the is relatively must expand with the rotor as i t gets flexible, it works without breaking. hot. Ifbolted the hat is relatively thin and The connection between the

flexible, it works without breaking. The bolted connection between the

25

Slots on Surface

Slots on Surface

,

Rotor Rotation Direction Curved Vent Holes Curved

Vent Holes Racing rotor from AP Racing uses a dogdrive rather than bolts to transfer braking action the from hat. Dogs on hatuses fit ina slots Racing to rotor AP Racing dogmachined in than edge bolts of rotor 10. Slightbraking cleardrive rather t o transfer ance between hatDogs dogsonand action t o the hat. hat rotor fit in slots allow rotorintoedge expand uniformly, but remain machined of rotor ID. Slight clearcentered. Cleverhat mounting arrangement is ance between dogs and rotor slots called rotor castel/a ted drive by AP allow t o expand uniformly, but Racing. remain Photo courtesy APmounting Racing. arrangement is centered. Clever

called castellated drive by AP Racing. Photo courtesy AP Racing.

On this racing rotor, metal is removed at outer edge to reduce weight and slots are cut in rotor faces to reduce of On this racing rotor, metal ispossibility removed at fade. Photo courtesy Racing. outer edge to reduceAP weight and slots are

cut in rotor faces to reduce possibility of fade. Photo courtesy AP Racing.

Highly developed AP Racing Sphericone rotor-notice projections cast inside ventJ holes-transmits cooling air more Highly developedheat AP to Racing Sphericone efficiently standardcast vented rotor-noticethan projections insiderotor. vent Design is used onheat Grand Prix cars, holes-transmits t o cooling airwhere more every ouncethan of rotor weight vented counts. Photo efficiently standard rotor. courtesy Racing. Design isAP used on Grand Prix cars, where

every ounce of rotor weight counts. Photo courtesy AP Racing. must use high-strength two items

bol ts wi th close-fitting, un threaded two items mustbolts use are high-strength shanks . Aircraft often used boltsthiswith close-fitting, for purpose, because unthreaded they come

shanks. Aircraft bolts are often used for this purpose, because they come 26

A rotor that has curved vent holes or angled slots must rotate in a particular direction be has effective. rotation A rotor tothat curvedCorrect vent holes or relative slots to vents and slots in is ashown. angled must rotate particular di-

rection to be effective. Correct rotation relative t o vents and slots is shown.

Here's what eventually happens to a rotor when thermal stresses are high. Because race-car rotors undergo such atobeating, Here's what eventually happens a rotor they should inspected and when thermalbestresses are frequently high. Because replaced ifrotors cracksundergo are detected. race-car such a beating,

they should be inspected frequently and replaced if cracks are detected.

with accurately machined unthreaded shanks. with accuratelyhats machined Aluminum reduce unthreaded weight and shanks. thermal stress on the rotor. Because Aluminum hatse xpands reduce atweight and aluminum alloy a gre ater thermal the to rotor. Because rate thanstress iron , itontends equalize the aluminum alloy expands at a greater expansion difference caused by exrate thantemperature iron, i t tends of to equalize ther. treme the roto expansion difference caused by exAdditionally , aluminum alloy is about treme temperature of the rotor. one-third as rigid as iron, so there is Additionally, aluminum alloy is about much less force put on the rotor fo r a one-third as rigid as iron, .so there is given amount of e xpansion The lightmuch less force put on the rotor for er aluminum hat aids the car ' s per-a given amount of expansion. lightformance and handling . One The disadvaner aluminum hat aids the car's tage of the aluminum-alloy hat is perthal formance handling. One iron. disadvanit conductsand heat better than This tage of the causes the aluminum-alloy wheel bearingshattois that* run ithotter. conducts heat better than iron. This causes the wheel bearings run Rotor Design-A disc-braketo rotor hotter. has many features common with that Rotor Design-A rotor of a brake drum. The disc-brake material is usualhas many that ly grey castfeatures iron forcommon the samewith reasons of a brake drum. The material is usualit is popular for brake drums. Cast ly greyhas cast good iron for the same iron wear and reasons friction itproperties, is popularis rigid for brake drums. and strong at Cast high iron has good and friction temperatures, and wear is inexpensive and properties, is rigid and strong at high easy to machine. temperatures, and is inexpensive and A rotor is measured by its outside easy to machine. diameter and its total thickness across rotorcontact is measured by its theA two surfaces. A outside vented diameter and its total thickness rotor is always thicker than aacross solid the two surfaces. A vented rotor. Thecontact diameter of the rotor is usurotorlimited is always than a solid ally by thethicker wheel size. rotor. Thearea diameter of theisrotor is usuSwept of a brake an imporally by of theitswheel size. tant limited measure effectiveness. The Swept area a brake imporswept area of of a disc brakeis isanthe total tant measure effectiveness. The area contactedofbyitsboth the brake pads swept of a disc brake is the total in one area revolution. area contacted by both thearea brakeofpads The combined swept a ll in one revolution. brakes divided by the weight of the combined swept area all carThe is one way of indicating how of effecbrakes by the the tive its divided brakes are likelyweight to be.ofWith

car is one way of indicating how effective' its brakes are likely to be. With

Tiny cracks on race-car-rotor surface are caused by thermal stresses. Rotor should be replaced before larger cracks form. Tiny cracks on race-car-rotor surface are Small cracksstresses. can oftenRotor be removed caised surface by thermal should by be grinding. replaced before larger cracks form.

Small surface cracks can often be removed by grinding. good brake design, high swept area

per ton indicates a high-performance

good design, swept brake brake system. Brake high swept area area for per ton cars indicates a on high-performance various is given page 28 . brake Brakeslots swept area mafor Somesystem. rotors have or holes various cars is given on page 28. chined in their contact surfaces . Some rotorshot-gas have slots holes maThese reduce and or dust-particle chined in their pad contact surfaces. buildup between and rotor. AlThese reduce hot-gas and dust-particle though fade caused by gas buildup is buildup padthan and for rotor. Alless for abetween disc brake a drum though fade caused by gas buildup is brake , some fade can still occur. This lessmore for a prevalant disc brakewith than large for a brake drum is brake, some fade stillhas occur. This pads , because the can hot gas a harder is more prevalant with large brake time escaping than with small pads. pads, because theorhot gas have has a greater harder Therefore, slots holes time escaping withpads small effect in racing,than where are pads. large Therefore, slots orareholes and temperatures veryhave high.greater Holes effect in racing, where pads large increase the tendency for are cast-iron and temperatures are very high. Holes rotors to crack, so they should be increase used only the whentendency required. for cast-iron rotors crack, so they be Vented to Rotors-Many rotoshould rs are cast used only when required. with radial cooling passages in them. Ventedact Rotors-Many rotors are cast These as an air pump to circulate withfrom radial passages in them. air thecooling rotor center through the These act as an air pump to circulate air from the rotor center through the

Tension Tenslon

1m I Compression Compression

Shear

Three ways stress act on a material: Tension pulls; compression crushes; and and shear rips rips Each stress occurs simultaneously in in a hot brake component, particularly particularly if one sideways. Each area area of the part is hot and and another is cool.

.' THEflMALSTRESS

Lightweight race-car rotor has has no hat. Rotor heat flows directly from rotor to t o aluminum minum hUb. hub. Such a design design should only be be used used on light cars with small small engines, where little heat is generated. Wheel bearings ings in in this hub hub have to t o be be replaced replaced several times a season.

'Stress is a measure of the internal force' inasolio material, usually giVen. in pounds per square inch (psj).:.,..the same units for measuring 'l1y-

(/J OJ (/J.:.t:.

OJ

ro

0: cO

O.4g

Ｈｾｲｏｰｯｴｩｮｧ＠

Changeover

Ｍｾ

Ｍ

ｾＭ

Ｍｾ

front and drums on rear. Drawing courtesy Bendix Corp.

Kelsey- Hayes adjustable proportioning valve was used on 1965-'68 Corvettes and some Ford products. It has been used Kelsey-Hayes adjustable proportioning for adjusting brake on many race valve was used on balance 1965-'68 Corvettes cars. ValveFord is adjusted loosening jam and some products,by has been used nut and turningbrake threaded shaft. for adjusting balance on many race

cars. Valve is adjusted by loosening jam nut and turning threaded shaft.

54

Relationship With Proportioning Valve

ldeal Relationship For Maximum Deceleration

Pressure In Front-

Ideal pressure curve plotted with curve from proportioning valve : Brake System (psi) At pressures above changeover pressure A , proportioning valve ldeal pressure curve with curve Notice from proportioning valve: reduces pressure riseplotted to rear brakes. that proportioning valve does notabove reproduce ideal curve, but itA,comes close . Without At pressures changeover pressure proportioning valve a proportioning valve pressure at pOint pressure to reduces pressure risemodifying to rear brakes. Notice thatA,proportioning rear brakes would continue to curve, rise in but direct proportion frontvalve does not reproduce ideal i t comes close.toWithout brake pressure. valve modifying pressure at point A, pressure to a proportioning

rear brakes would continue t o rise in direct proportion to frontbrakepressure.

valve comes t o this ideal curve, the faster a car will stop under inside theany combination condition.

This proportioning valve looks like a brake fitting. It contains a spring-loaded valve that changes pressure-rise rear This proportioning valve looksrate like atobrake brakes. IValves sucha as this are found in fitting. t contains spring-loaded valve many changes production cars with disc brakes on that pressure-rise rate to rear front andValves drums such on rear. brakes. as Drawing this are courtesy in Bendixproduction Corp. many cars with disc brakes on

Without Proportioning

Valve Relationship With Valve

Pressure In FrontBrake System (psi)

Pressure in Front-Brake System (psi) Upper curve represents ratio of front-to-rear brake Pressure in Front-Brake System (psi)pressures in system not using a proportioning valve. Pressure ratio is built into master cylinder or balance Ideal pressure relationship Upper curve represents ratiobar. of front-to-rear brake pressuresfor in maximum regardless of surface, is ratio shown in lower system notdeceleration, using a proportioning valve. Pressure is built into curve. would bar. look ldeal like this if brake system could masterPressure cylinder curve or balance pressure relationship for automatically proportionregardless pressures ofto surface, make front and rear tires maximum deceleration, is shown in lower reach a system proportioning curve. traction-limits Pressure curvesimultaneously. would look likeThe this closer if brake could valve comes toproportion this ideal curve, the faster a carfront will stop any automatically pressures t o make and under rear tires condition. reach traction-limits simultaneously. The closer a proportioning

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valve. Therefore, don't be concerned if you inside find the combination can't a metering valve on valve. your Therefore, don't be concerned if you car as a sepa rate unit. Metering valves can't find a used metering valve on even your are seldom on race cars, car a separate unit. Metering valves withasdisc/drum-brake setups because are seldom on very race hard, cars, and evena race braking used is done with disc/drum-brake setups because metering valve isn't needed in hard race braking is done very hard, and a braking. metering valve isn't hard The metering valve needed operatesin much braking. like a residual-pressure valve. A The meteringpoppet valve valve operates much spring-loaded is seated like a residual-pressure valve. A with a precise amount of spring ｦｯｲ｣ｾＮ＠ spring-loaded poppet valve is seated When hydraulic pressure exerts suffiwith aforce precise of spring force. cient on amount the poppet, the spring When hydraulic pressure exerts suffiforce is overcome and the poppet cient force on the poppet, the spring opens to aJlow fluid flow. Another force is allows overcome the through poppet passage fluid and return opens to allow fluid flow. Another the valve when the brake(s) is passage allows fluid return through re leased. the valve when the brake(s) is

BRAKE BALANCE As discussed in Chapter 1, a car unBRAKE BALANCE dergoes weight transfer during a carfront unAs discussed braking. WeightinisChapter added to1, the dergoes transfer during wheels as itweight is removed from the rear braking.inWeight is amount. added toThe the probfront wheels the same it is removed from the wheels as lem is that braking force should berear apwheels the same The probwheelamount. in proportion to plied toineach lem weight is that braking force weight, should be apthe on it-more more plied to and eachvice wheel in proportion to braking, versa. theWeight weighttransfer on it-more weight, more depends on vehicle braking, and vice versa. deceleratio n deceleration. Maximum Weight mostly transferondepends vehicle depends frictiononbetween deceleration. Maximum deceleration the tires and road surface. If the fricdepends mostly of on the friction tion coefficient tires between is high , the tires and road surface. fricdeceleration is high, as Ifis the weight tion coefficient of surface the tireswith is ahigh, transfer. On a slick low deceleration is high, is weight friction coefficient, bothasdeceleration transfer. Ontransfer a slick are surface and weight low . with a low

friction coefficient, both deceleration and weight transfer are low.

Correct brake balance means that front-to-rear braking forces are proCorrect so brake balance means that portioned neither front nor rear front-to-rear braking forces are prowheels lock first. Pu t another way, the portioned so neither front norsimulrear front and rear brakes wiJl lock wheels lock iffirst. Put another way, the taneously correctly balanced. If front andwas rearadjusted brakes will lock simulbraking to be equal on taneously if correctly balanced. If both the front and rear wheels , a hard braking adjusted be equal on stop withwas high weight to transfe r would both the and rear wheels, a hard cause the front rear wheel to lock up first. If stop with high weight transfer the brakes were proportioned onwould thi s cause rearbraking wheel tooccurred lock up on first.the If car so the more yropot.tiot?ed on this the brakes were front, the car could stop quicker. car so more braking occurred the Greatest deceleration occurs onwhen front, the car could stop quicker. both front and rear tires reach their Greatest deceleration occurs traction limit at the same time . when Tires both frontmaximum and rear grip tires ju reach their develop st before traction at the same time. Tires they slid.limit Remember, slatic friction is develop maximum grip just before higher than sliding/riction. they slid. Remember, static.fr.iction is Correct slidingfriction. brake balance is different higherthan for high deceleration than for low . Correct brake for balance is different Brakes balanced dry pavement will for deceleration thanpavement. for low. not high be balanced for wet Brakes balanced for dry will For examp le , a hard stoppavement on wet pavenot be balanced for wet pavement. ment will give less deceleration than For example, a hard stop on wet pavefo r dry pavement; less weight transfer ment will less wheels deceleration than occurs and give the front lock up. forAdry pavement; less weight transfer system that corrects the various occurs and the front iswheels lockProporup. traction conditions needed. A system that corrects the various tioning valves are designed to do this. traction conditions issystem needed, hasPt.opor.a cerA hydraulic-brake tionirig valves are designed to do this. tain ratio between front and rear A hydraulic-brake a cerbrake pressures. A system tandemhas mastertain ratio between front and rear cylinder brake system with equal brake pressures. A tandem masterpiston diameters has the same prescylinder brake system with equal sures front and rear. This means that piston diameters thewith same presif you push on thehas pedal enough sures front and rear. This means that force to produce 100 psi in the front if YOU lines push , on pedal withlines enough brake thethe rear brake will forcehave to produce 100them. psi inIf the also 100 psi in you front step

brake lines, the rear brake lines will also have 100 psi in them. If you step

down harder and raise the pressure to 400 psi, both front and rear brakes down harder and raise the pressure to will have 400-psi pressure. This is not 400ideal psi, situation both front rear brakes an for and maximum stopwill pressure. This is not pinghave on all400-psi surfaces. anLet's ideal assume situation that for maximum we have astopcar ping all surfaces.disc brakes . Disc with on four-wheel Let's have assume that we havesoa that car no servo action, brakes with four-wheel disc brakes. Disc simplifies this example. Let 's also brakes have action, are so that assume that no all servo four brakes the simplifies thisdiameter example.andLet's also same-rotor caliperassume thatare all the four brakes the piston sizes same. Thisare means same-rotor diameter and caliperthat the torque output of the brakes is piston sizesfront are the means the same and same. rear ifThis front and that the torquepressures output ofare thethebrakes rear hydraulic same.is theWesame frontassume and rear front will also thatif the car and has rear hydraulic pressures are the same.of a 50/50 weight distribution-50% will also assume that wheels the car and has theWe weight is on the front a50% 50/50 distribution-50% of is onweight the rear. If we make a panic the weight is on the front wheels and stop on a slick surface , weight transfer 50% is onzero. the rear. we maketorque a panic is nearly EqualIf braking is stop on a from slick surface, weightand transfer desired both front rear is nearlyIfzero. Equal braking torque we are trying to stop in is a brakes. desired from both front and rear hurry on ice, the condition of hard brakes. we are to stop in a brak ing Ifwith lowtrying weight transfer hurry on ice, exist. the condition of hard might actually braking Now lewith t's trylowto weight design atransfer brake might actually exist. system that gives maximum Now let's regardless try to design brake deceleration, of thea coeffisystemof friction that between gives themaximum tires and cient deceleration, regardless of the coeffithe road. This brake system would cient of friction between tires and have to adjust the ratio the of pressures the road.thThis brake would between e front and system rear brakes to have to adjust ratio of in pressures account for thethe difference weight between the and brake rear brakes to transfer. Thefront ideal system

account for the difference in weight transfer. The ideal brake system

flects high deceleration rates obtained with high tire grip and the resulting flects deceleration rates obtained weighthigh transfer.

would be designed to lock all four wheels at once, regardless of weight would transfer.be designed to lock all four wheels once, onregardless weight In theatgraph page 54, ofI plotted transfer. the relationship between front- and In the graph on page plotted rear-brake pressures for 54, our Iexample the relationship between frontcar. If master-cylinder-piston sizes and are rear-brake our example equal , therepressures is alwaysforequal pressure car. If master-cylinder-piston sizes are in the front- and rear-brake systems. equal, there is always equal This is the straight line in thepressure graph . in the the frontand rear-brake systems. When pressure in the front-brake This is the in the system is straight doubled,linethe reargraph. also When the pressure in the front-brake doubles. This is not ideal for maxisystem is doubled, thevarious rear tracalso mum deceleration under doubles. This is not ideal for maxition conditions. mum under various tracWithdeceleration a high-traction surface, tion conditions. weight transfer increases. This reWithlessa pressure high-traction quires at the rearsurface, brakes weight transfer increases. This the reand more at the front because quires pressure at the reartires brakes verticalless force on the front is and more thethe front because the greater thanat on rears. A brake vertical with forceequal on brake the front tiresand is system pressure greater than on the rears. A brake equal brake torque will lock the rear system equal wheels with before the brake fronts.pressure This is and not equal brake will lock the rear desirable fortorque maximum deceleration wheels beforeA the This is rear not or stability. car fronts. with locked desirable for maximum deceleration wheels and rolling front wheels will or spinstability. easily. A car with locked rear wheels and rolling front the wheels The lower curve shows ratio will bespin easily. tween front-and rear- brake pressures The lower curve shows ratio beautomatically changed to the account for tween frontandItrear-brake weight transfer. shows thepressures need to automatically changed account for the to percentage of gradually reduce weight transfer. It shows the needrear to brake pressure going to the gradually reduce increased. the percentage of brakes as traction This re-

with high tire grip and the resulting weight transfer. PROPORTIONING VALVE

Now that we have an ideal frontPROPORTIONING to-rear brake-pressureVALVE curve for this an the idealstraightfrontcar,Now howthat can we we have modify to-rear brake-pressure curve forclose this line pressure relationship to get car, how can we modify the straightto the ideal curve? Answer: It is done line relationship with pressure a proportioning valve. to get close to Atheproportioning ideal curve? Answer: It is done valve reduces the with a proportioning pressure increase tovalve. the rear brakes. A does proportioning reduces the This not meanvalve that pressure to pressnre increase to the rear the rear brakes is preven tedbrakes. from This does merely not mean to rising-it risesthat at apressure lower rate the rear brakes ispressure prevented froma than front-brake when rising-it merely riseschangeover at a lower presrate specified pressurethan front-brake pressure when sure-is reached. Th e curve of front-a specified pressurecharigeover presto-rear- brake pressure with a proporstlre-is valve reached. Therear curve of line fronttioning in the brake is to-rear-brake pressure with plotted in the graph, page 54 . a proportioning valve in the rear brake curves line is The accompanying pressure plotted the graph, pageaxes 54. because do not in have numbered Thevary accompanying pressure they with each car. Exactcurves presdo not have numbered axes because sures in a brake system vary with they vary with each car. Exact brake preshydraulic-cylinder dimensions, sures a brake systemweight vary with location, and design,in CG hydraulic-cylinder brake wheelbase of the dimensions, car. The curve design, has CGthelocation, weightin and always shapes shown the wheelbase of the car. The curve two figures, but the numbers vary always the shapes shown in the from carhas to car. twoMost figures, but the numbers proportioning valves vary are from car to car. preset at the factory . They cannot be Most orproportioning are adjusted serviced later. valves Each valve

brake pressure going to the rear brakes as traction increased. This re1100

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AP Racing Adjustable Proportioning Valve CP 2611-3 Adjustable AP Racing

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100 Tilton Engineering offers this AP Racing adjustable proportioning valve. Lever has five positions, each with a different changeover pressure. Valve is ideal road occasionally raced on racing Tilton Engineering offersfor this APcar Racing adjustable proportioning tires. weight each transfer racing tires means valve. Improved Lever hasgrip fiveand positions, withwith a different changeover less pressure should go to Photo courtesy AP Racing. pressure. Valve is ideal forbrakes. road car occasionally raced on racing

tires. Improved grip and weight transfer with racing tires means less pressure should go to brakes. Photo courtesy AP Racing.

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changes to rear brakes. With valve at setting 2, pressure rises as if thereshows were no until 200-psi proportioning-valve changeover point is pressure reached. Graph APvalve, Racing adjustable Pressure tothen at With a lesser This effectively changes rearrises brakes. valverate. at setting 2, pressure reduces rises as pressure-rise rate to rear delays orpoint prevents rearif there were no valve, until brakes 200-psiand changeover is reached. wheel lockup. Tiltonrate. Engineering, Inc. Pressure thenGraph risescourtesy at a lesser This effectively reduces

pressure-rise rate to rear brakes and delays or prevents rearwheel lockup. Graph courtesy Tilton Engineering, Inc.

55

is suitable for use only on the car for which it was adjusted. This is unfortuis suitable for you use may only like o n the car for nate because an adjustwhich it was adjusted. This unfortuable proportioning valve as ais means of nate because youhigh-performance may like an adjustbalancing your or able proportioning valve as a means of race-car brakes. Fortunately, some balancing yourvalves high-performance or proportioning allow an external race-car brakes. some adjustment. Some Fortunately, of these are shown proportioning valves photos. allow an external in the accompanying adjustment. S o m e of these are shown Porsche, Chrysler, Chevrolet and in the accompanying photos. Ford have adjustable proportioning Porsche, Chrysler, Chevrolet and valves for high-performance use. The Ford have proportioning Porsche 914 adjustable uses an adjustable val ve valvescanForbehigh-performance use. T h ea that changed by loosening Porsche 914 uses an adjustable valve lock nut and turning a screw. Turning that screw can beinward changed by loosening the on this valve putsa lock and turning a screw. morenut pressure on the rear Turning brakes the screw inward o n this valve puts during a hard stop. Adjusting the more ispressure o n the rear brakes valve a trial-and-error process, as during a inhard stop.10.Adjusting the described Chapter valve a trial-and-error as The isChevrolet Corvetteprocess, adjustable described in Chapter 10. proportioning valve, 3878944, is T h e Chevrolet Corvette adjustable available both from Chevrolet and proportioning valve, specializing 3878944, in is from racing shops available both fromChrysler's Chevroletvalve, and brake components. from racingis available shops specializing in P4120999, through their brake components. Chrysler's valve, performance-parts division, Direct P4120999, is available their Connection. Ford's through proportioning performance-parts division, through Direct valve, M-2328-A is available Connection. Ford's dealers. proportioning Ford Motorsport These valve, M-2328-A valves work muchis available the samethrough as the Ford dealers. begins These PorscheMotorsport valve. Proportioning valves work much t h e same as the between 100 and 1000 psi, depending Porsche valve. Proportioning begins where adjustment is set. between 100 and 1000 psi, depending Another proportioning val ve, where adjustment is set. which operates like the Porsche and Anothervalves, proportioning Corvette is available valve, from which operates like and Alston Industries the of Porsche Sacramento, Corvette valves, available from California. This oneis was designed by Alston Airheart Industries Sacramento, Frank to goof with his highCalifornia. o n e was designed by performanceThis dual, tandem master Frank Airheart to go with his highcylinder. performance dual,valve tandem master A proportioning is installed in cylinder. line between the master cylinder and valve in theA proportioning rear brakes. It willis installed work with line between cylindercylinand either a singlet hore amaster dual master the inrear will work with der the brakes. system, Itbecause all it does either a single or a dual master cylinis affect the maximum pressure at the der in t h e system, because all it does rear brakes. is An affect t h e maximum pressure valve, at the adjustable proportioning rear brakes.is sold by Tilton EngineerCP2611-3, proportioning ingA n ofadjustable Buellton, California. valve, This CP2611-3, is sold by Tilton Engineerdevice can be mounted in the cockpit inga race of car Buellton, Thisit of so the driCalifornia. ver can adjust device can be mounted in the acockpit during a race. He can move lever of a anyone race car so the driver canpositions adjust it into of five different during a race. H e can move as brake or track conditions, aorlever the into anydistribution o n e of five of different weight the carpositions changes as brake o r track conditions, or the during a race. weight distribution the car changes Curves of inlet ofpressure versus during a race. outlet pressure for this valve are Curves of inlet pressure versus shown on page 55. Note that pressure outlet for this are rises in pressure a one-to-one ratio valve until the

shown o n page 55. Note that pressure rises in a one-to-one ratio until the 56

Inlet and Outlet ,-------- Ports are 7/1624 Thread for 3/16Inlet and Outlet or 1 /4-in.-OD Ports are 7/16-Tubing 24 Thread for 3/16or 1/4-in.-OD Tubing

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Kelsey-Hayes adjustable proportioning valve is available from Kelsey Products Division Front-Brake Pressure (PSI) and many U.S. automobile dealers through their high-performance catalogs. Valve functions the same as APadjustable RaCing valve except it'svalve infinitely adjustable between and 1000 psi. Kelsey-Hayes proportioning is available from Kelsey100 Products Division Adjustments are made withdealers thumbscrew. courtesy Kelsey-Hayes Corp. automobile throughDrawing their high-performance catalogs. Valve functions and many U.S. the same as AP Racing valve except it's infinitely adjustable between 100 and 1000 psi. Adjustments are made with thumbscrew. Drawing courtesy Kelsey-Hayes Corp.

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Ideal Front vs. Rear Fluid Pressure Relationships For Different Weight Distributions ldeal Front vs. Rear Fluid Pressure Relationships For Different Weight Distributions Car A Car weight, wheelbase, and CG height are Tail-Heavy Car the same for all three cars. Only With front-to-rear weight distribution varies.are Car A40/60 Weight Car weight, wheelbase, and CG height DistributionCar Tail-Heavy the same for all three cars. Only With 40/60 Weight front-to-rear weight distribution varies. Distribution Car B

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Pressure In Front-Brake System (psi) cars with different weight Ideal front-to-rear brake-system pressures for three different distributions: Nose-heavy car has less pressure to rear wheels; tail-heavy car has more. Ideal front-to-rear brake-system pressures for three different cars with different weight distributions: Nose-heavy car has less pressure to rear wheels; tail-heavy car has more.

changeover pressure is reached. For position 5, pressure rises as if the prochangeover pressure For portioning valve is notis inreached. the system position 5, pressure rises as if the prountil about 950 psi is reached. At that portioning valve is not inpoppet the system point, the spring-loaded valve until about 950 psi is reached. that inside the proportioning valve At opens, point, the spring-loaded poppet valve and output-pressure increase is reinside with the proportioning valve opens, duced increasing input pressure. and output-pressure increase is reMeanwhile, front-brake pressure is duced with increasing not affected. It increasesinput as it pressure. did withMeanwhile, front-brake out a proportioning valve. pressure is notMost affected. increases as it did withroad Itcars have proportioning out a proportioning valve. valves that give approximate correct Mostbalance road cars brake withhave an proportioning average load

valves that give approximate correct brake balance with an average load

using street tires. If the car is set up for racing, its total weight, weight using street and tires.tire If grip the car set up distribution are islikely to for racing, its total weight, weight change from the average values the distribution and tire arebrake likelybalto car was designed for. grip Thus, change the average valueseven the ance mayfrom be incorrect for racing, car was designed for. Thus, brake balthough it has a proportioning valve. ance may be incorrect for racing, even Remember, a proportioning valve thoughtheit approximate has a proportioning gives correct valve. brake Remember, proportioning balance over aa limited range of valve tracgives the approximate correct brake tion conditions. balance range of tracIf you over drivea a limited car on the street and tion conditions. race it on occasion, you may want to youadjustable drive a car o n the streetvalve and useIf an proportioning

race it o n occasion, you may want to use a n adjustable proportioning valve

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to change brake balance. For street driving, the car should be correct as to For change brake balance. street is. racing, brake balanceFor probably driving, should be tocorrect as havethe to car be readjusted provide will is. For racing, brake balance probably more braking force on the front-less will haverear. to be readjusted to provide on the Racing tires have more more than braking forcetires; on the front-less grip street thus, weight on the rear. Racing under tires have more transfer is greater maximum grip than street tires; thus, weight braking . transfer is greater maximum Let's say you haveunder a sports car that braking. you drive to work and slalom on the Let's say With you have a sports car that weekends. the quick-adjustable you drive to work and on the Tilton valve, you don't slalom even have to weekends. With the quick-adjustable get your hands dirty. In the example Tilton valve, yourun don't to given, you might the even valve have at posiget In drop the example tion your 5 for hands street dirty. use and to posigiven, the valve at posi4 reduces tion 4 you for might racing run . Position tion 5 for street use and drop to posirear-wheel braking, starting at a lower tion 4 forthan racing. Position 4 reduces pressure position 5. This comrear-wheel starting at a translower pensates forbraking, the greater weight pressure than position 5. This fer when braking on racing comtires. pensates for setting the greater weightbalance transMore about up brake fer when 10. braking on racing tires. in Chapter More about setting up balance One disadvantage of brake proportioning in Chapter 10. valves is that they increase pedal One without disadvantage of proportioning effort reducing displacement valves high-deceleration is that they increase during stops. pedal effort without reducing displacement If you wish to add a proportioning during stops. valve tohigh-deceleration a car that doesn't have one, If you to does add anot proportioning make surewish the car have a diagvalve to a car thatsystem doesn't have rearone, brake . Some onally split not have a diagmake sure the car does wheel-drive cars and most frontonally split brake system. Somesorearwheel-drive cars are designed the wheel-drive and most left-front andcars right-rear brakesfrontare wheel-drive carssame are designed so the operated by the half of a tandem left-front and right-rear brakes are master cylinder; right-front and leftoperated by the same half of a tandem rear brakes are operated by the other master cylinder; and alefthalf of the masterright-front cylinder. With direar brakes arebrake operated by the other agonally split system, a single half of the master cylinder. valve With awill diadjustable proportioning

agonally split brake system, a single adjustable proportioning valve will

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In different Front-Brake System (psi) Two ideal pressure curves Pressure for cars of weight distributions show how one proportioning valve can be adjusted to work with either. Two ideal pressure curves for cars of different weight distributions show how one proportioning valve can be adjusted t o work with either.

not work. It only works where both rear brakes are fed by a single hydraunotline. work. I t only works where both lic I cover adding a proportioning rear brakes are fed by a single hydrauvalve to an existing car in Chapter 12.

lic line. I cover adding a proportioning valve to an existing car in Chapter 12. PRESSURE-LIMITING VALVES

A pressure-limiting valve is used on PRESSURE-LIMITING VALVES some cars with disc brakes on the A pressure-limiting valve is used on front and drums on the rear. It persome with function disc brakes on the forms cars a similar as a proporfront drums on pressure-limiting the rear. It pertioningandvalve. The forms a similar function as ata the proporvalve prevents the pressure rear tioning valve. The pressure-limiting brakes from exceeding a preset value. valvedifference prevents the pressure at the rear The between a proportionbrakes from exceeding a preset value. ing valve and a pressure-limiting

The difference between a proportioning valve and a pressure-limiting

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valve can be seen by comparing the accompanying graphs. valve be seen by between comparingpressure the acThecan relationship companying graphs. in the front-brake system and rearThe system relationship between brake is shown in thepressure graph , in the Note front-brake and rearhow thesystem pressure-limiting below. brake system shown in the graph, valve differs isfrom a proportioning below. Note how the pressure-limiting valve . Remember, a proportioning valve differs the from a proportioning valve allows pressure in the rear valve. proportioning system Remember, to rise if thea driver pushes valve pressure rear harderallows on thethe pedalbut atina the reduced system to rise if the driver pushes rate. However, a pressure-limiting harder the pedal-but reduced valve on limits pressure toat athe rear rate. However, a pressure-limiting brakes. valve pressure rear Whenlimits this preset valueto is the reached,

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Honda Civic has diagonally split braking system with two proportioning valves. Valves are shown at bottom. One adjustable proportioning cannot besplit used with system diagonally braking Honda Civicvalve has diagonally braking withsplit two proporsystem.valves. Two proportioning valves at willbottom. work, but tioning Valves are shown Oneadjustment adjustable must probe synchronized. Portioning valve cannot be used with diagonally split braking

Relationship between front- and rear-brake system pressure of pressure-limiting valve : Compare curve to that of ideal pressure curve on pagebetween 54. Withfronta proportioning valve, system pressure continues Relationship and rear-brake pressure of to rise in rear-brake system beyond changeover With pressure-limiting valve: Compare curve to that of pressure. ideal pressure pressure-limiting changeover pressure is continues reached, curve on page 54.valve, With aonce proportioning valve, pressure that's as it gets. For a high-performance car,pressure. use a proporto riseasinhigh rear-brake system beyond changeover With tioning valve, not avalve, pressure-limiting valve-unless car is extremepressure-limiting once changeover pressure reached, ly nose-heavy. that's as high as i t gets. For a high-performance car, use a propor-

system. Two proportioning valves will work, but adjustment must be synchronized.

tioning valve, not a pressure-limiting valve-unless car is extremely nose-heavy.

57

Both proportioning valves are adjusted by spring between rear axle and proportioning-valve lever. Valve adjustment changes with rearsuspension travel from weight on rear wheels. Rear-axle movement moves lever and changes valve setting. As weight on rear wheels increases, so doesvalves rear-wheel-brake pressure. Cars that suchproportioning-valve large weight-distribution changes, such changes as this with Plymouth Both proportioning are adjusted by spring between rearhave axle and lever. Valve adjustment rearVoyager/Dodge Caravan (left) or stationRear-axle wagon (right), will benefit from a height-sensing proportioning suspension travel from weight onPeugeot rear wheels. movement moves lever and changes valve setting. valve. As weight on rear wheels increases, so does rear-wheel-brake pressure. Cars that have such large weight-distribution changes, such as this Plymouth Voyager/Dodge Caravan (left) or Peugeot station wagon (right), will benefit from a height-sensing proportioning valve.

pressure to the rear brakes cannot increase, regardless of how hard the pressure to the on rear the brakes cannot driver pushes pedal. A increase, regardlessvalve of how hard well the pressure-limiting works driver on the pedal. A only on pushes an extremely nose-h eavy car, pressure-limiting valve workssedan. well such as a front-wheel-drive only an extremely nose-heavy car, pressure-limiting valves usually Also,on such as a front-wheel-drive sedan. are not useful for race cars because Also, pressure-limiting most are not nose heavy.valves usually

are not useful for race cars because most are not nose heavy. ANTI-SKID SYSTEM A nti-skid systems are designed to

ANTI-SKID prevent wheelSYSTEM lockup, no matter how Anti-skid sysrenls are designed to the brakes are applied. hard prevent wheel lockup, how Many manufacturersno clmatter aim their hard the brakes applied. properties. systems have are anti-skid Manytheymanufacturers claim their What real ly do is prevent one systems havefrom anti-skid pair of wheels locking properties. before the What they reallya good do is propo prevent one other. In a sense, rtioning pair ofiswheels from locking the valve an anti-skid device;before it keeps other. In awheels sense, from a goodlocking proportioning the rear before valve is an In anti-skid device; I itdiscuss keeps the fronts. this section, the rear wheels from locking before systems other than.!7xedproportioning thepressure-limiting fronts. In this section, valves. I discuss or systems than.fixedproportioning Some other anti-skid devices amount to or pressure-limiting valves. propornothing more than adjustable Some anti-skid devices to some extioning valves controlled byamount nothingmeans. more The thanvalve adjustable proporternal is adjusted by tioning valves controlled by some rear-suspension movement or exby ternal means. The valve is adjusted by sensing the actual decelera tion of the rear-suspension movement or by car. The type that operates from rearsensing the actual deceleration of the suspension movement compensates car. The that operates rearfor bothtype deceleration andfrom vehicle suspension movement compensates weight. This is particularly important fora both deceleration and vehicle in truck or a station wagon, where weight. is particularly the CG This can move a great important deal with in a truck or a instation wagon, changes in load the cargo area. where the CG can move a great with The anti-skid valve thatdeal senses changes in load in the cargo area. deceleration uses the bal/-and-ramp The anti-skid valve that senses prinCiple. The valve is positioned so deceleration theup,ball-and-ramp that the rampuses angles toward the principle. Thevehicle. valve isThe positioned so front of the valve conthat the ramp angles up, toward the front of the vehicle. The valve con58

tains a conventional proportioning valve and a bypass. At low tains a conventional proportioning deceleration, brake fluid passes the valve a bypass. At low ball andand bypasses the proportioning deceleration, brake fluid passes the valve, regardless of pressure. At a preball and bypasses the proportioning determined transition decelerationvalve, of pressure. about regardless 0 .3 g-the ball rollsAtupa prethe determined transition ramp, closes the bypass,decelerationand proporabout g-the ball rolls up the starts. tioning 0.3 ramp, and proporThis closes valve the canbypass, compensate for a tioning starts. changing CG location . As weight at compensate theThis rear valve of thecan vehicle increases,forthea changing C G location. As weight at rear suspension compresses and the the rear of the vehicle This increases, the ramp angle increases. increases rear the the suspension transition compresses decelerationand and, ramp angle increases. This increases therefore, rear-brake pressure at the transition deceleration and,transition. Thus, the rear brakes share rear-brake pressure at atherefore, larger portion of the braking. transition. the rear brakessenses share A true Thus, anti-skid system awhen largera wheel portionstarts of thetobraking. lock . It closes a A true senses line to system that wheel to valve in theanti-skid when a wheel starts to It lock. It closes reduce the pressure. then sensesa valvewheel in the line toup that to the speeding and wheel reapplies reduce the pressure. It then senses pressure. A typical system uses the wheel sensors speeding to up sense and reapplies magnetic wheel pressure. A typical system uses speed. magnetic sensors to are sense Wheel-speed signals sent wheel to an speed. electronic module, or computer, Wheel-speed sent to an which computessignals wheelare deceleration electronic module, computer, and slip values for eachor wheel. Decelwhich computes wheel deceleration eration and slip values for that wheel and slip values for each wheel.for Decelare compared with values the erationwheels and slip for that wheel other andvalues with fixed thresholds are compared for are the (preset values) . with Whenvalues thresholds other wheels and with fixed thresholds exceeded, the module sends a signal (preset values). When thresholds the proper controller. The valveare is to exceeded, module a signal and the pressure to sends that wheel is closed to the proper controller. valve is reduced. When wheel The deceleration closed pressure to thatlevels, wheeltheis and slipand go below threshold reduced. When wheel deceleration module signals the controller to inand slippressure go below threshold levels,hapthe . All this shuttling crease module signals the hard controller to inpens rapidly during applications,

crease pressure. All this shuttling happens rapidly during hard applications,

ATE skid-control front-wheel sensor, introduced on '85 Lincoln Mark VII, is ilATE skid-control front-wheel sensor, lustrated on display model with sectioned introduced '85 Lincoln VII,speed is ilfront-wheel onrotor/hub. As Mark wheel lustratedrapidly on display sectioned changes whenmodel brake with lockup begins, front-wheel rotor/hub. wheel speed brakes are rapidly cycled As on and off to prechanges rapidly when brake lockup begins, vent lockup. Photo by Tom Monroe. brakes are rapidly cycled on and off to prevent lockup. Photo Monroe. wheel (s)by Tom never completely so the

lock. so theControllers wheel($ require never an completely Note: external lock. power source, which can be hydraulic, Note: Controllers electric or vacuum. require an external power source, which can behave hydraulic, Skid-control systems been electric or vacuum. used on large aircraft since the '50s. Skid-control systems have been The first vacuum-powered road-car used on developed large aircraftby since the '50s. systems Kelsey-Hayes The Delco first were vacuum-powered and introduced in road-car the late systems developed by Chrysler. Kelsey-Hayes '60s by Ford, GM and The and Delco were systems introduced in the late Ford and GM operated on '60s rear by Ford, andChrysler Chrysler.had Thea the wheelsG M only; Ford and Gsystem. M systems operated on four-wheel Porsche experithe rear wheels only; Chrysler had mented with mo re sophisticated sys-a four-wheel system. experitems in the early '7 0s Porsche on 911 and 917 mented race cars.with more sophisticated systems in the early '70s car on manufactur911 and 917 Today, most major race cars. ers are developing four-wheel Today, 1984 most Porsche major carand manufactursystems. Mercedes ers are developing models use Bosch anti-skidfour-wheel systems, systems.and 1984 Porsche and Honda Mitsubishi haveMercedes systems models use Bosch anti-skid systems. in production, Ford introduced a

Honda and Mitsubishi have systems in production. Ford introduced a

Safety Braker is fancy cylinder mounted in brake line from nearest master cylinder. It damps Braker pressure pulses in brake fluid, Safety is fancy cylinder mounted in giving more consistent brakingcylinder. and less brake line from nearest master It pedal pulsation. is slightly difficult damps pressureIt pulses in more brake fluid, to lock more one wheel with a braking Safety Braker in giving consistent and less the device is an pedal system. pulsation. Because It is slightly more difficult accumulator, it displaces fluid Braker and into lock one wheel with a Safety in creases pedal travel slightly. Safety isBrakthe system. Because device an ers are no longer made. fluid and inaccumulator, it being displaces

Three different types of mechanical stoplight switches each have plunger to operate electrical switch. Usually, switch is operated by movement of brake pedal. Drawing courtesy Bendix Corp. types of mechanical stoplight switches each have plunger to operate Three different

electrical switch. Usually, switch is operated by movement of brake pedal. Drawing courtesy Bendix Corp.

creases pedal travel slightly. Safety Brakers are no longer being made.

system developed by ATE for the 1985 Mark VII. GM released systems system developed by and ATE ATE for the developed by Bosch for 1985 Mark VII. G M released systems 1986 models. These systems are developed but by they Bosch and much ATE imfor expensive, provide 1986 models. systems are proved directionalThese stability, steerabiliexpensive, but they provide much imty and deceleration in critical braking proved directional stability, steerabilimaneuvers on all road surfaces. ty Anti-skid and deceleration in critical braking systems can provide maneuvers all road surfaces. these same on advantages in racing, plus Anti-skid systems provide they can eliminate tire can flat spotting. these same advantages in racing, plus To date, an ti-skid systems have been they can eliminate tire flat spotting. used little because of their weight and To date, anti-skid systems have been questionable reliability. However, used little because of their weight and recent advancements in technology questionable reliability. However, should change that. Many highrecent advancements in technology powered, exotic road-racing cars will should Many highprobably change be using that. anti-skid devices by powered, road-racing will 1990. But exotic for now, a skilledcars racingprobably feel be using anti-skid devices by driver's is considered to be the 1990. But for now, a skilled racingmost effective anti-skid device. driver's feel is considered to be the most effective anti-skid device. STOP-LIGHT SWITCHES Stop-light switches are either meSTOP-LIGHT SWITCHES chanical or hydraulic. Both are conStop-light are either menected to theswitches electric circuit and turn chanical or hydraulic. Both are conon the brakelights when activated. nected to the electric circuit and turn The hydraulic switch is designed as a on the brakelights when activated. hydraulic fitting and is operated by The hydraulic pressure. switch is The designed as a brake-system mechanihydraulic fitting and is operated by cal type is operated directly by brakebrake-system pressure. The mechanipedal-linkage motion. Most newer cal type is operated directly by brakecars use the mechanical switch. pedal-linkage motion. newer With both switch types,Most the electricars use the mechanical switch. cal circuit is open until the brakes are With both switch types, the electriapplied. When the switch closes, the cal circuit open until the brakes the are stop lightsis illuminate. Usually, applied. When theisswitch closes, the mechanical switch designed to close stop lights illuminate. Usually, the mechanical switch is designed to close

Hydraulic stoplight switches screw into a fitting in hydraulic system. Fluid pressure operates switch. Although easier to install, mechanical switches are better for racing. HydrauliC switch takes a smallswitches amount of fluid into movement to in operate it, and a mechanical switch operdoes Hydraulic stoplight screw a fitting hydraulic system. Fluid pressure not. Also, hydraulic switches leak. Drawing courtesy Bendix ates switch. Although easier can to install, mechanical switches are Corp. better for racing. Hydraulic

switch takes a small amount of fluid movement to operate it, and a mechanical switch does not. Also, hydraulic switches can leak. Drawing courtesy Bendix Corp.

when the brake pedal has been moved about 112 in. The hydraulic switch is when the tobrake beenpressure moved designed closepedal with has a small 112 in. The hydraulic switch is about buildup in the system . The exact designed to close with a small pressure point at which the switch closes is not buildupbecause in the any system. exact critical modestThe brake appoint at which theclose switchthe closes is not plication should electrical critical because any modest brake apcontacts. plication close the electrical If you should are selecting a stop-light contacts. swi tch for a race car, use a mechanical If . you are selecting stop-light type Although more adifficult to switch for a race car, use a mechanical install, a mechanical switch will not type. the Although moreif itdifficult to affect brake system fails. A hyinstall, switch a mechanical switch will not draulic is just another possible affect the brake system it fails. A hyleak. Also, slight fluid ifmovement is draulic switch is just another necessary for operation. Everypossible possileak. Also, must slightbefluid movement ble failure eliminated from isa necessary race car. for operation. Every possible failure must be eliminated from a race car. WARNING-LIGHT BRAKE SWITCHES BRAKE Brake WARNING-LIGHT warning-light switches have SWITCHES been in use since tandem master cylinBrake ders werewarning-light introduced in switches the '60s. have This been in use since tandem master cylinpressure switch illuminates a warning ders introduced in the '60s.which This light were on the instrument panel, pressure switch illuminates a warning light on the instrument panel, which

indicates a problem with the brake system. The switch senses any indicates a problem with the brake hydraulic-pressure imbalance between system. The switch senses any the front and rear brake systems. hydraulic-pressure imbalance between And, the light · illuminates when a the and-rear brake systems. presetfront pressure imbalance occurs. And, will thewarn lighttheilluminates when a driver of problems This preset as pressure occurs. such fluid imbalance leaks, masterThis will warn tlie driver in the cylinder-fluid bypass or ofairproblems such leaks, mastersystem. as fluid cylinder-fluid air in the A typical bypass brake orwarning-light system. switch is shown on the following page. warning-light AtAthe typical center of brake the switch, a piston is switch following page. located isbeshown tween on twothe spri ngs. Pressure At the center of the switch, a piston is from the front brakes is on one side of located between two springs. Pressure the piston and rear-brake pressure is from frontDifferences brakes is oninone of on thethe other. theside force thethe piston and rear-brake pressure is of two springs compensa te for the on the other. pressure Differences in the force designed-in differential of of two springs compensate the thethefront and rear systems. for When designed-in pressure differential severe pressure differential occ ursof, the front and rear toward systems.theWhen the piston is moved lowsevere pressure differential pressure side . This closes the occurs, switch the turns pistononisthe moved toward and warning light.the lowpressure side. This closes the of switch There are many variations this and turns on the warning light. simple switch . Some have centering There are many variations of this simple switch. Some have centering 59

Brake WarningLight Switch

Brake WarningPiston Off-Center

Stem

houlder of Piston Touching Terminal

Brake warning-light switch is indicating hydraulic-system malfunction. Piston between two centering springs is pushed to left by higher pressure in right chamber. Piston contact with electrical terminal turns on instrument-panel warning light. malfunction. Drawing courtesy Corp. Brake warning-light switch is indicating hydraulic-system PistonBendix between two

centering springs is pushed t o left by higher pressure in right chamber. Piston contact with electrical terminal turns on instrument-panel warning light. Drawing courtesy Bendix Corp.

springs; some even have two pistons. The switch type used varies with the springs; even have two pistons. design ofsome car and brake system.

near the master cylinder so lines to the front and rear brakes can be easily near the master cylinder so lines to connected to the valve.

In recent years, car manufacturers COMBINATION VALVE have combined the function of the In recentvalve, years,proportioning car manufacturers metering valve havebrake combined the function and warning-light switch of intothea metering valve, proportioning valve single combination valve. Some manuand brakecombine warning-light switch into a facturers the brake warningsingle combination valve. Some manulight switch with either the proporfacturers combine the brake warningtioning valve or the metering valve. light switch with either the Some front-wheel-drive carsproporwith tioning valve orsystems the metering valve. combine two diagonally-split Some front-wheel-drive with proportioning valves with cars the brake diagonally-split systems combine two warning-light switch. Because external proportioning valves with the brake appearances of these valves are warning-light similar, be switch. careful Because when external moving appearances of these are brake-system componentsvalves from one similar, be careful when moving car to another. Check part numbers brake-system components from one and car shop manuals to be sure. carCombination to another. valves Check are partfound numbers only and car shop manuals to be sure. in brake systems using a tandem Combination are found master cylinder.valves Usually, they only are in brake systems usingdisca and tandem found on cars with front rear master brakes. cylinder. Most Usually, they are drum combination found on cars with front disc and rear valves cannot be disassembled for drum brakes. Most combination service or adjustment. If defective, a valves cannot be disassembled for be replaced. valve must service or adjustment. If defective, Combination valves work similar toa valve must be replaced. the individual valves they replace. By Combination work similar to combining in avalves common housing, the individual valves replace. By fewer fittings are used.they Consequently, combining a common the valve isinsimpler, costs housing, less and fewer fittings are used. Consequently, leak possibilities are reduced. thePictured valve isis simpler, less and a typical costs three-function leak possibilities are reduced. combination valve. The metering Pictured is a the typical three-function valve operates front system and combination valve. The the proportioning valve themetering rear. A valve operates the must front be system and combination valve mounted

A fluid-level indicator consists of a FLUID-LEVEL INDICATOR device in the fluid reservoir and a A fluid-level indicator brake warning light. It consists switchesofona device in the fluid reservoir and aa when reservoir fluid drops below brake warning level. light. This It switches on predetermined indicating when reservoir fluid drops device consists of a float andbelow a me-a predetermined level. This indicating chanically or magnetically actuated device consists of a float and a meswitch. chanically or magnetically actuated Like the brake warning-light switch. switch, low fluid-level indicator warns brakeleakswarning-light theLike driverthe of fluid or masterswitch, low fluid-level indicator cylinder bypass. It can also warns signal the of fluid leaksbutornot masterworndriver disc-brake linings, air in cylinder bypass. It can the system. Usually, twoalso are signal used worn linings,cylinders. but not airBein with disc-brake tandem master the system. Usually, two are used cause fluid-level indicators perform with master cylinders. Bemany tandem of the same functions as brake cause fluid-level indicators perform warning-light switches, they are rarely many of the same functions as brake used together.

The switch type used varies with the design of car and brake system. COMBINATION VALVE

the proportioning valve the rear. A combination valve must be mounted 60

Three-function combination valve combines metering valve, proportioning valve and brake warning-light switch Three-function combination valve into com-a single metering unit. Metering is at leftvalve end bines valve, valve proportioning and proportioning valve is under brake warning-light switchlarge intonut a on bottom. courtesy Bendix Corp. single unit.Drawing Metering valve is at left end

and proportioning valve is under large nut on bottom. Drawing courtesy Bendix Corp.

the front and rear brakes can be easily connected to the valve. FLUID-LEVEL INDICATOR

warning-light switches, they are rarely used together. HOSES Hydraulic fluid is carried to the cali-

HOSES pers or wheel cylinders by flexible Hydraulic is carried to the calihoses. Thesefluid hoses allow suspension perssteering or wheel cylinders by flexible and motion. hoses. suspension In theThese early hoses days ofallow the automobile, and steering motion. high-pressure flexible hoses did not In the early days ofitthe exist. Consequently, wasautomobile, difficult to high-pressure get hydraulic flexible fluid to hoses brakesdid at not the exist. it was difficult to wheels.Consequently, It was amazing that early get hydraulic fluid to brakes at the hydraulic-brake systems worked at wheels. amazing that Fluid Itwaswas routed through axleearly and all. hydraulic-brake workedThis at suspension links systems to the brakes. all. Fluid was routed through axlefront and was particularly difficult on the suspension links seals to thewere brakes. wheels. Sliding usedThis to was particularly difficult on the front allow steering and suspension wheels. Sliding seals were used to allow steering and suspension

Although old, cracked brake hose stills holds pressure; it should be replaced. Condition of outSide rubber is the only to Although old, cracked brake hoseway stills judge condition of a brake It's better holds pressure; it should behose. replaced. Conto replace a cracked hose than to way risk to a dition of outs~de rubber is the only suddencondition brake failure. judge of a brake hose. It's better

to replace a cracked hose than to risk a sudden brake failure.

motion . To contrast this, the modern brake hose is simple and reliable. motion. To contrast this,from the multiple modern Brake hoses are made brake hose is simple and reliable. layers of fabric impregnated with Brake hoses areThey made are from multiple synthetic rubber. tough and layers of years, fabricbutimpregnated with last many are still the weaksynthetic They are tough Itand est link inrubber. the hydraulic system. is last many years, but are still thecontact weakeasy to damage a hose through est the hydraulic It is withlinka in wheel, tire , system. suspension easy to damage a hose through contact member, exhaust or road debris. Or with a wheel, tire, can suspension an overzealous mechanic damage exhaust or road debris. Or amember, brake hose during installation. A an overzealous mechanic can brake hose can fail if twisted damage or imaproperly brake installed hose during installation. A . brake hose can fail if imBrake hoses expand twisted slightly or under properly installed. high internal pressure. This swelling Brake additional hoses expand under requires fluid slightly movement to high internalfor pressure. This swelling compensate the increased hose requires The additional movement to volume. driver fluid senses hose swellcompensate for the increased hose ing or expansion as a soft or spongy volume. The driver sensesand hose swellbrake pedal. Racing high-

ing or expansion as a soft or spongy brake pedal. Racing and high-

Imperial tube bender is available from good tool stores. Neats bends can be made without risk of crimping Beforefrom youI good bend Imperial tube bendertube. is available brake lines, Neats invest bends in a good bender. withtool stores. cantube be made "Ultimate" brake hoses are steel-braided teflon. Because exterior is braided stainless steel, hoses more resistant to me"Ultimate" brake are hoses are steel-braided chanicalBecause damage than is ordinary teflon. exterior braided rubber stainhoses. Steel-braided hoses areto mealso less steel, hoses are more resistant stiffer, giving a firmer pedal. chanical damage than ordinary rubber

hoses. Steel-braided hoses stiffer, giving a firmer pedal.

are

also

Don't use high-pressure plastic tubing for a brake hose! After repeated flexing, tubing cracks at fittings. I've seentubing this failDon't use high-pressure plastic for urebrake on several cars.repeated Plastic tubing is a hose!race After flexing, also easily damaged by heat mechanical tubing cracks at fittings. I've or seen this failcontact. Although tubingtubing can be ure on several raceplastic cars. Plastic is usedeasily if rigidly mounted to frame, weight also damaged by heat or mechanical saved isn't worth risking brake failure. contact. Although plastic tubing can be

out risk of crimping tube. Before you bend brake lines, invest in a good tube bendler.

used if rigidly mounted to frame, weight saved isn't worth risking brake failure.

performance brake systems require that rubber brake hoses be replaced performance with somethingbrake better.systems require that rubber brake hoses be replaced High-pressure stainless-steelbraidwith something ed brake hoses, better. developed for aircraft High-pressure and military use,stainless-steel-braidare available from ed brake hoses,. Suppliers developedare forlisted aircraft specialty shops at and military use, are available from the back of the book. Steel-braided specialty Suppliers are listed at hoses areshops. available in custom lengths the of the book.to Steel-braided with back adapter fittings suit special hoses are available custom applications. These inhoses are lengths Teflon with adapter fittings to suit lined and externally reinforcedspecial with applications. These are almost Teflon stainless-steel braid. hoses They are lined and externally reinforced with "bulletproof' and resist expansion stainless-steel braid. They are almost under pressure. "bulletproof' and resistTeflon-lined expansion Aeroquip 6600-series under pressure. hose with Super Gem fittings is a type Aeroquipused 6600-series Teflon-lined commonly on race cars. I highly hose with Super G e m fittings is a hose type recommend this flexible brake I highly commonly used on race cars. to make the brake pedal firmer, and recommend this flexible brake hose for overall safety. Remember, use to make hose the brake flexible only pedal wherefirmer, thereand is for overall safety.components Remember,being use motion between flexible hoseEven onlythewhere is connected. best there flexible motion between components being hose expands more under pressure connected. Even the best flexible than steel hydraulic tubing. hose expands more under Some race cars use plastic pressure hose for than hydraulic tubing. both steel the brake tubing and the flexible Somehoses. race cars plastic hose for brake Thisuse tubing may work bothsome the brake tubing andapplications, the flexible for low-pressure brakeit ishoses. This tubing mayflexible work but dangerous to use as for some low-pressure applications, brake hose. Plastic tends to crack but it isthe dangerous to usethe as flexible where tube enters fitting. brake repeated hose. Plastic After flexing,tends even to thecrack spewhere the developed tube enters cial fittings for the this fitting. tubing Afternotrepeated spe-a will preventflexing, failure. even If youthe have cial fittings for this tubing race car withdeveloped plastic brake hoses, rewill not prevent If you Teflon have a place them with failure. steel-braided

race car with plastic brake hoses, replace them with steel-braided Teflon

hoses. Failure of the plastic hose will occur without warning and cause hoses. Failure the plastic hose will sudden brakingof loss.

occur without warning and cause sudden braking loss. HYDRAULIC TUBING

Most cars use tubing manufactured HYDRAULIC TUBING from steel for the brake system. ComMost cars use tubing manufactured monly called brake lubing, it is availafrom steel for the brake system. Comble in diameters from 1/8 in . through monly is availa3/8 in.called Mostbrake of tubing, today ' sit cars use ble in diameters 118 in, through 3/16-in. tubing ;from 1I4-in. tubing is 318 in.onMost today's use found most ofolder cars. cars Smaller 3116-in. tubing;and114-in. tubing is tubing is stiffer lighter and easier found most tubing older has cars.less Smaller to bend.onLarger resistubing stiffermovement and lighterand and iseasier tance tois fluid less to bend. Larger tubing has resis-. prone to damage during less handling tance3/16-in to fluid movement less The .-diameter tubeand is aiscomprone damage atduring promiseto arrived after handling. years of The 3116-in.-diameter tube is a using comexperience. I recommend promise arrived at after years of 3/16-in . hydraulic tubing for all brake experience. I recommend using systems. 3116-in. for all brake Copperhydraulic tubing ortubing any tubing of an systems. unknown material should never be Copper tubingtubing or any tubing isofsoft an used for brake . Copper unknown material should never be and prone to cracking. Ordinary steel used formay brake Copper isbut soft tubing be tubing. strong enough, it and pronemeet to cracking. doesn't the rigidOrdinary quality steel and tubing may be strong but it design standards of enough, brake tubing. doesn't meet the rigid quality and Tubing manufactured for brake sysdesignby standards of brake tubing. tems Bendix is made of soft-steel Tubingsheathed manufactured for brakeThese sysstrips with copper. tems by Bendix is made of soft-steel strips are then rolled into a doublestripstube sheathed with at copper. These wall and bonded high temperastrips in area then rolled a doubletures furnace . Theinto tu be is then wall tube and at highresistance. temperatin-coated forbonded corrosion tures in a furnace. The tube is then Ordinary steel tube is only single wall tin-coated for corrosion resistance. and not copperor tin-plated. It could Ordinary steela few tubeyears is only wall rust out after andsingle suddenly

and not copper- or tin-plated. It could rust out after a few years and suddenly

Automotive brake-tubing flares : Doubleflare used on most American cars is at left; at right is iso-flare used on some Doubleforeign Automotive brake-tubing flares: cars. used Flares match fittings toat which flare on must most American cars is left; they attach, otherwise a leak or failure will at right is iso-flare used on some foreign result.Flares must match fittings t o which cars.

they attach, otherwise a leak or failure will result.

Making double flare: Flaring tool comes with dies needed to do both forming operations. Tool flare: and tubing aretool set comes up to Making double Flaring do second with dies forming neededoperation. to do both forming

operations. Tool and tubing are set up to do second forming operation.

61

Flaring tool folds tube end back on itself to finish double-flaring operation. Drawing courtesy Chrysler Corporation. Flaring tool folds tube end back on itself to

finish double-flaring operation. Drawing courtesy Chrysler Corporation.

Fittings used with steel-braided hose are different than standard automotive brake fittings. High-pressure steel-braided-hose fittings meet aircraft standards, not automotive standards. Special adapter fittings aircraft-type fittings to automotive brakes. Fittings used with steel-braided hose attach are different than standard automotive brake fittings. Photo courtesy C & D Engineering Supply Ltd. meet aircraft standards, not automotive High-pressure steel-braided-hose fittings

standards. Special adapter fittings attach aircraft-type fittings to automotive brakes. threads. Accompanying Photo courtesy C & D ~ n ~ i nphotos eerin supply g show Ltd. seat for the flare they mate to.

Race cars often require fittings not normally found in auto-parts stores. Bulkhead fitting handy mounting lines Race is cars often for require fittings brake not normalwhere they pass through a panel such fitas ly found in auto-parts stores. Bulkhead this fire wall. Two nuts support ting is handy for jam mounting brake fitting lines at hole they in panel. where pass through a panel such as

this fire wall. Two jam nuts support fitting at hole in panel.

burst. Always use proper-quality brake-tubing material, available from burst. Always auto-parts stores. use proper-quality brake-tubing material,tubing available from Double Flare-Brake is availaauto-parts stores. ble in several standard lengths with Doublefittings Flare-Brake is availamale at each tubing end. Common ble in several standard lengths are 8, 12, 20, 30lengths , 40, 50 with and male at each end. diameters Common 60 in . fittings Commonly available lengths 40, 50 cars and are 3/16are or 8, 11412, in. 20, for 30, American 60 in. Commonly available diameters and 3/16 in. or 4.762mm for imported 114 isin.doubleIlared-tube for American cars are 3/16 cars. Eachorend and 3/16 in. or 4.762mm for imported is doubled over on itself-in a convex cars. Each end is double7/lared-tube or concave shape. American and imis doubled itself-in flares a convex ported carsover useondifferent and

or concave shape. American and imported cars use different flares and 62

some of these differences. threads. photosforshow DoubleAccompanying flares are important the some of these differences. strength and safety of a brake system. Doublewith flares are important for can the Anyone a cheap flaring tool strength and safety of a brake system. make single flares. NEVER singleAnyone with a cheap brake lines. If youflaring don't tool wantcan to flare make single flares.double-flaring NEVER singleinvest in a special tool, flare lines.brake If you tudon't to buy brake preflared bes want or pay invest in a special double-flaring tool, someone to custom-make double buy preflared brake are tubes or will pay flares. Single flares weak, someone custom-make doublea eventually to fatigue, crack and cause flares. Single flaressystem. are weak, will leak in the hydraulic eventually fatigue, crack cause toa Armor-Brake tubing is and exposed leak in the hydraulic system. harsh conditions under a car. It gets Armor-Brake tubing is isexposed to blasted by dirt and debris, immersed harsh conditions under a car.continue It gets in water and salt, but should blasted by dirt debris, is immersed to function forand years without failure. in water and salt, but should Anytime you are under your continue car, look to function for years without for brake-line damage . A failure. rusty, Anytime you are look kinked, nicked or under leakingyour line car, must be for brake-line damage. A rusty, replaced. If you want extra protection kinked, leaking must be with newnicked brakeortubing , itline is available replaced. with If you want extra This protection wrapped a coil spring. armor with new the brake tubing, is available protects tube fromit damage by wrapped with asharp coil spring. armor rocks o r other objects.This Armored protects the can tubebe from by brake lines founddamage in major rocks or other sharp objects. Armored au to- parts stores.

brake lines can be found in major auto-parts FITTINGSstores.

Brake lines are connected with steel FITTINGS or brass fittings of various types, such are connected steel as Brake tees, lines junction blocks andwith unions. or brass fittings of various types, such Be careful when selecting brake-line as tees, They junction blocks fittings. must have and the unions. correct

Be careful when selecting brake-line fittings. They must have the correct

Otherwise, they will leak. Many fit-

seat for look the OK flare matepropto. tings that willthey not mate Otherwise, theytubing. will leak. Many erly with the Never use fittatings OK will mate proppered that pipelook threads in a not brake system. erly with use taThey will the leak tubing. under Never high pressure, pered pipe threads in a brake system. particularly if installed without They willThey leak will underalso highsplit pressure, sealant. when particularly if installed without overtorqued. sealant. They will switches also split when Some stop-light have taovertorqued. pered pipe threads. They will seal if Some tape stop-light switches have you taTeflon is used . However, pered pipe threads. sealanyif must be very careful They not towill allow Teflon tape tape to is extend used. However, you Teflon past the first must be very careful not to allow any thread. A shred of Teflon tape floating Teflon tape to extend past the first around in the brake fluid can plug a A shred ofsystem. Teflon tape thread. port in the The floating best socritical around in the brake fluid plug a lution is avoiding the use can of tapered critical port in the system. The best sopipe threads. Take a tip from the airlutionindustry: is avoiding theTeflon-tape use of tapered craft Leave seapipe threads. Takeand a tippipe fromfitters. the airlant to plumbers It craft industry: Leave Teflon-tape seacan cause many problems in a brake lant to plumbers and pipe fitters. It system. canOncause in a brake race many cars, problems steel-braided hoses system. are used to improve reliability and On race cars,brakes. steel-braided provide firmer Fittings hoses used are used to improve reliability and with steel-braided hoses are different provide firmer used than those usedbrakes. with Fittings conventional with are different different hoses.steel-braided They have hoses entirely than those used with conventional specifications for threads, flares and hoses. dimensions. They have entirely other Adapter different fittings specifications threads, flaressteeland must be used for when installing other dimensions. Adapter fittings braided hoses on vehicles with must be used when automotive-type brakeinstalling fittings. steelbraided hoses on with Adapter fittings are vehicles available from automotive-type brake fittings. Adapter fittings are available from

Of

·c

*F

'C

600

'E

500

ｾ＠

300

Selected High BoilingPoint Glycol Brake Fluids elected High Boiling-

20e 250

oint Glycol Brake '0 al 300

20c

ＲｯＰＡＭＧ［ｾＳＮＺＶＱ＠

150

Weight % Water 1

Brake tube in fitting fractured during a race, causing complete brake failure. Driver but luckily Brake was tube without in fittingbrakes, fractured during ita happened where complete he could recover race, causing brake without failure. crashing. Failure occurred because fittingDriver was without brakes, but luckily it mounting was installed. happened bolt where henot could recoverVibrating without fitting andFailure hose occurred was supported byfittingtube, crashing. because which eventually failed fatigue. Brake mounting bolt was not from installed. Vibrating tubes and must supported be securelybymountfitting andfittings hose was tube, ed to prevent suchfailed failure. which eventually from fatigue. Brake

tubes and fittings must be securely mounted prevent such theto sources thatfailure. supply the hoses,

such as e & D Engineering Supply the that supply the hoses, Ltd., sources or WREP Industries. Some such asoffer C &brake-hose D Engineering Supply shops kits that inWREP Industries. Some Ltd., or clude ada pter fittings and correctshops that inlength offer hoses.brake-hose Don't mixkits automotive cludeaircraft adapter fittings correctand fittings. This and will result in length hoses. Don'tleaks mix automotive damaged threads, or cracked and aircraft Thisrecognize will resultthe in fittings. If fittings. you can't damaged threads, leaks or cracked difference, ask the adv ice of a shop fittings. If you recognize the that supplies thesecan't fittings. difference, ask the advice shop Adapter-fitting usage will ofbea minithat supplies these fittings. mized if a race car is constructed using usage will besystem. miniall Adapter-fitting aircraft fittings in the brake mizedcan if aberace carbyis getting constructed using This done the proper all aircraft fittings in the brake system. fittings from an aircraft hardware This can be done getting supplier. You maybystill havethe toproper adapt fittings fromlineCs) an aircraft the brake to yourhardware master supplier. You still using have automoto adapt cylinder(s) andmay brakes the brake line(s) to your master tive flares or fittings. cylinder(s1 and brakes using automoAircraft flar es are not the same as tive flares or fittings. automotive flares. They use Aircraft flares are notthe the tubes same as ferrules-sleeves-over to automotive They and use reinforce them. flares. Aircraft hoses fitferrules-sleeves-over tubes AN to are identifiedthe as tings reinforce them. Aircraft and fit(Army-Navy) or MShoses(Mi litary tings are AN identified AN Standards). and MSas specI(Army-Navy) or M S (Military fications, written by the U.S. Standards). ANstandards and MS specigovern ment , are recognized fications, by Automotive the U.S. throughout written the world. government, specifications are are standards written byrecognized the Societhroughout the world. Automotive ty of Automotive Engineers (SAE) . specifications arealso written by the SAE standards have the Sociesame ty of Automotive Engineers (SAE). worldwide recognition .

SAE standards also have the same worldwideFLUID recognition. BRAKE Once a brake system is installed, it

BRAKE must be FLUID filled with fluid so it can Once a brake system is installed, it must be filled with fluid so it can

Brake fluid is lifeblood of any brake system. For race cars, you must keep fresh new fluid in brake system atof all times. Fluid Brake fluid is lifeblood any brake with highest possible boiling is a system. For race cars, you must point keep fresh must for raCing. new fluid in brake system at all times. Fluid

with highest possible boiling point is a must for racing.

function. Hydraulic fluid for an automotive brake system is simply function. Hydraulic for an aucalled brake fluid. Thisfluid distinguishes it tomotive system simply from fluidsbrake used for other ishydraulic This distinguishes it called brakefluid. applications and systems. Automotive from fluids used for other hydraulic brake fluid is designed to work the applications Automotive brake systemand of asystems. car. Other hydraulic brake have fluid totally is designed to work the fluids diffe rent chemical brakephysical systemproperties. of a car. Other hydraulic and Always use aufluids have totally tomotive brake fluiddifferent in a car.chemical Aircraft and physical properties. Alwaysand use aubrake fluid is totally different will tomotive brake not work in a car.fluid in a car. Aircraft brake fluid is totally differentmixture, and will Brake fluid is a chemical not work in a car. which varies with manufacturer. Each Brake fluid has is aa chemical mixture, manufacturer secret formula dewhich varies with manufacturer. signed to perform a "better job ."Each All manufacturer has a secret formulatheir demanufacturers must formulate signed to perform a "better brake fluid so it m ee ts rigid job." SAE, All inmanufacturers must formulate their dustry and government standards. In brake fluid it meets rigid SAE, inthe U.S. , thesoDepartment ofTranspordustry and government standards. In tation (DOT) sets the standards. theHydraulic U.S., the brake Department of Transporfluid used in racing tation (DOT) sets the standards. and road cars is mostly a Polyalkylene Hydraulic brakemixture-commonly fluid used in racing Glycol Ether and road cars is mostly a Polyalkylene called glycol. This type of fluid can be Glycol Ether mixture-commonly found in any auto-parts store and is called glycol.with Thisthetype fluid can inbe compatible fluidoforiginally found in store type and of is stalled in any yourauto-parts car. A newer compatible fluid originally brake fluid with has the a si licone base . inIts stalled in A newer type of properti es your differcar.from glycol-based brake fluid has a silicone base. fluids . Silicone-based brake fluid Its is propertieslater differ from glycol-based discussed in this chapter. fluids. Silicone-based brakemust fluid is Glycol-based brak e fluid have discussed later in this chapter. the following properties to work corGlycol-based brake fluid must have rectly in an automobile: the following properties to work • Must not boil at tempera tures corenrectly in an automobile: countered during severe braking Must not conditions . boil at temperatures en-

countered during conditions.

severe

braking

300 250

2

3

4

5

I00 6

Weight % Water Graph shows how boiling point of glycolbased brake fluid drops with exposure to moisture. Notice how brakepoint fluid with highGraph shows how boiling of glycolest boiling when with new exposure is affected based brakepoint fluid drops to most by Notice water how content. courtesy moisture. brakeGraph fluid with highYankee Silicones, est boiling point Inc. when new is affected most by water content. Graph courtesy Yankee Silicones, Inc.

• Must not freeze or thicken in cold temperatures. Must not not compress. freeze or thicken in cold • Must temperatures. • Must flow through system passages Must not compress. minimal no res istance. with Must passages not through corrode system or react with • Must flow with minimal no resistance. brake-system materials. not corrode or sliding react parts with Must lubricate internal • Must brake-system materials. of brake system. Must lubricate sliding parts • Must not alter internal its properties after of brake system.for extended periods. being in system its properties after Must not be alter compatible with other • Must being in system for extended periods. glycol-based brake fluids . Must not be decompose, compatible orwith form other gum • Must glycol-based brake fluids. or sludge at any temperature. Must Boiling-The not decompose,most or formcritical gum Fluid or sludge at any temperature. property of brake fluid is its resistance Fluid Boiling-The most critical to boiling at high temperature. When property of brake fluid is its resistance brake fluid boils , small bubbles form. to boiling at high temperature. When These bubbles collect and are trapped brake boils,Because small bubbles form. in the fluid system. gas bubbles These bubbles collect and are trapped are compressible, this results in a in the brake system. Because gas bubbles spongy pedal. areBoiling compressible, this results in a generally is caused by water spongy brake pedal. vapor being absorbed by the brake Boiling is caused by water fluid . Thegenerally mo re water brake fluid vapor being absorbed by the brake contains, the lower its boiling point. fluid. more water high-quality brake fluid New,The uncontaminated, contains, lower its boiling point. brake fluidthe boils at 550F ＨＲＸ･Ｉ ｾ＠ pure New, uncontaminated, high-quality water boils at 212F (lOOe). A mixture brake fluidfluid boilsand at 550F pure of brake water(288C); boils somewater at 212Fthese (100C). A mixture where boils between temperatures. of brake fluidpoints and water boils someare referred to in Two boiling where between these temperatures. brake-fluid specifications: dry boiling Two boiling points paint. are referred in wet bailing Withouttogetpoil1l and brake-fluid specifications: dry boiling of the specifications, ting into details and wet should boilingpoint. Without getpoint the meaning be clear. Dry boilting into details of the specifications, ing point refers to fresh fluid out of a

the meaning should be clear. Dry boiling point refers to fresh fluid out of63a

,B RAKE-FLUID SPECIFICATIONS The print on brake-fluid cans is 8RAKE-FLUID SPECIFICATIONS confusing. Even worse, specifica- , The on constantly, brake-fluidsocans is tions print change an old confusing. worse, specif icacan of fluid Even may say something diftions constantly, an old ferent change than a new can . Theso following can may say something difis of an fluid explanation ' of current ferent than a new can. The following specifications. is Allan explanation of current brake fluids must meet federal

standard 116. Under this standard are three Department of Transportastandard Under thisfor standard tion (DOT)116. specifications brakeare Department of Transportafluidthree performance : DOT 3, DOT 4 tion (DOT) and DOT 5. specifications All brake fluidsfor arebrakesuitafluid DOT 3, or DOT 4 ble forperformance: use in either drum disc and DOTBoiling 5. All brake are suitabrakes. pointfluids for the three ble forof use either drum or disc types flu,i dsinare as follows:

specifications. All brake fluids must meet federal

brakes. Boiling point for the three types of fluids are as follows:

Dry Boiling Point

Degrees F , Degrees C

Dry Boiling Point

Degrees F

Wet Boiling Point

Degrees F Degrees C Degrees C

Wet Boiling Point

Degrees F Degrees C

DOT3

DOT 4

DOTS

401 DOT 3 205

446 DOT 4 230

500 DOT 5 260

40 1 284 205 140 284 140

446 311 230 155 31 1 155

500 356 260 180 356 180

it.

I ｾ＠

I

e

a ap:!

:-

[ s~ RACinG 550 Racing 5 5PlUld 0 BtaWl

"k

I"IGt contents 1 hre

us Brake 338 us II", id ＢｾＬ＠

Iqtl81101 rkatr*nlmlm

U Sr "

e-':I l •• 1" 5

1 1 H U S Ilrv 1 , 18 ~ t t , ~ , . I

..

ｾ＠ ｾ＠

ｾ

700

'we

600 Ｌ＠

!j'"9 m u

500

'" o

5ｾ＠

503400

ｾ＠::l

300

y

Ｌ ｾ＠

Typical Glyco l-Based {Brake Fluid Typical Glycol-Based

g 200 L----'-----'1'-2---':18---'---'

Months in Service , I I I I 200 6 24 Curve shows what 'I2 happens18 to boiling Months inbrake Service point of glycol-based fluid in typical road-car use. , toWeather Curve shows what happens boiling changes point of curve'-boiling glycol-based point brakegradually fluid in drops in extremely climates. Sili,typical road-cardamp, use. Weather cone brake fluid is not point susceptible to changes curve-boiling gradually moisture as it· damp doesn't pick Siliup drops in extremely climates. moisture. Consequently, silicone cone brake fluid is not susceptible to ｉ｢ｲ｡ｫ･Ｍｦｬｵｩ､ moisture as ｾ ｢ｯｩｬｮｧ＠ remains it' point doesn't pick high up moisture. silicone after long Consequently, use. Graphcoi!rtesy brake-fhid boilingInc. point remains high Yankee Silicones, after long use. Graph courtesy Yankee Silicones, of a fluid is by lnc. its DOT number. A

UC-,~

AP 550 Racing Brake Fluid is used ｾ＠ . in ,most-severe racing applications. Its dry 550 boiling pointBrake of 550F AP Racing Fluid(288C) is used is h ' highest for a glycol-based fluid, Photo most-severe racing applications. Its courtesy APpoint Racing. dry boiling of 550F (288C) is highest for a glycol-based fluid meetsfluid. DOTPhoto 2 or Old brake courtesy AP Racing. , SAE J1703 or 70R3 specifications.

Old brake fluidrequirements meets DOT refer 2 or These obsolete SAE 31 703 specifications. to , fluid withora 70R3 dry boiling paint of These obsolete requirements 374F (190C). If you have any ofrefer th is to a dryit. boiling point of old fluid fluid,with discard Don't use any374F (190C). If you have this thing less than DOT 3 any fluidof in a old fluid, discard it. Don't anybrake system . Prior to theuse DOT 2 thing less thanthere DOT was 3 fluid in a specifications, a 70Rlbrake system.brake 2 Prior fluid to the DOTfor specification meant specifications, there was this a 70R1drum brakes only. Throw away specification for too if you find brake any. Itfluid has ameant dry boildrum brakes only. Throw this away ing paint of only 302F (150C). tooSpecified if you find boiling any. It has a dry boilpoints are ing point of only 302F (150C). minimums. Many brake fluids have Specified points are higher boiling boiling points, as indicated minimums. Many brake fluids have on their containers. As for what to highera dry boiling points, asover indicated use, bailing point 500F on theiris containers. for what to (260C) best for hardAs driving. use, a 3dryand boiling over 500F DOT DOT point 4 specifications (260C) is best for hard driving. are for glycol-based brake fluid and DOT and DOT 4You specifications DOT 5 is3 for silicone. can tell imare for glycol-based brakechemistry fluid and mediately what the basic DOT 5 is for silicone. You can tell immediately what the basic chemistry 64

glycol-based

brake

fluid

with , a

of a fluid is bydry its boiling DOT number. A 500F(260C) point is glycol-based tested to DOT 3brake or DOT fluid 4, not with DOT 5.a 500F (260C) dry boilingpoint point is Sometimes boiling tested to to DOT 3 o r DOTon 4, not OT5 referred asERBP the DbrakeSometimes point is fluid can. This boiling means' equilibrium referred to aspoint, ERBPwhich on the brakeisanothreflux boiling fluid can. This means equilibrium er way of saying wet boiling point. reflux boiling whichin is anothERBP refers topoint, a method the speer way offor saying wet is boiling point. cification how fluid exposed to ERBP refers a method in. the spemoisture and to tested . cification forfluid howboiling fluid isｰ exposed to ' Note that ｾ ｯｩｮｴ＠ drops moisture tested.to water. Glycolafter it isand exposed Notebrake that fluid boiling point drops based fluids absorb moisture. after resulting it is exposed to water. GlycolThe mixture of brake fluid based brake fluids in absorb moisture. and water results a ｢ｯｩｬｮｧｾｰｴ＠ The of brakewater fluid drop.resulting Fluids mixture that · absorb and water in' a hydrostopic. boiling-point ' easily areresults called drop. Fluids that absorb water Water in brake-fluid also causes easily hydroscopic. corrosionare and called impurities to accumuWater in hydraulic brake-fluid also causes late in the system. corrosion and impurities to accumulate in the hydraulic system.

sealed can ; wet boiling point refers to fluid that has been exposed to moissealed can; wet boiling point refers to ture under specific conditions . Both fluid that has been exposed to moisboiling points should be of concern to ture, under conditions. you but thespecific most important oneBoth will boiling points should be of concern Lo de pend on how you use your car. you, but the most important one will Dry boiling point is important for depend you usethat youracar. racing . on It ishow assumed properly Dry boiling i s important for m aintained racepoint car will always have racing. I t is assumed that a properly fresh brake fluid, For best permaintained race car must will always have form ance, the fluid be changed fresh brakeduring fluid.a racing For best many times seasonperto formance, the boiling fluid must changed avoid a lower point.beCh anging many timesis during a racing season the fluid an inexpensive way to to avoid a lower boiling point. Changing ensure the brakes work bes t at temthe fluid encountered is an inexpensive to peratures in racingway . ensure the brakes best at temWet boiling pointwork is most important peratures n racing. for street encountered use , Brake ifluid in streetWet boiling point is most driven cars is not changed important often-if for Brake fluid i n streetever.street If youuse. could bleed your brakes driven week cars isornot often-if every so ,changed the brake fluid ever. I fhave you could bleedsimilar your brakes would properties to a every week or who so, can thetake brake race car's. But, the fluid time would have their properties similar to a to bleed brakes weekly? race car's. But, canmust take function the time Normally, the who brakes to bleed their brakes weekly? with moisture in the brake fluid over Normally, the brakes must function long periods of driving during all with the brake fluid over types moisture of weathe irnconditions. long periods o f driving during all Brake fluids with a high wet boiling types o f weather conditions. point do not necessarily ha ve the highfluids with boiling estBrake dry boiling point.a high Mostwet racers use do not necessarily have the ahighapoint glycol-based brake fluid with dry est dry boiling Most(288C) racers use bo iling point point. of 550F for a glycol-based brakehigh-performance fluid with a dry racing. A common boiling point (288C)is AP for brake fluid usedo fin 550F road racing A common high-performance racing. Racing 550 . This fluid exceeds DOT 4 brake fluid used roadboiling racing point, is AP specifications fori ndry Racing 550. This fluid exceeds DOT and meets DOT 3 specifications for4 specifications for dry boiling point, wet boiling point. To maintain your and meets Dsystem O T 3 specifications racing-brake properly, it isfora wet boiling good choice . point. To maintain your racing-brake properly, s a For street system use, you shouldi t iuse good choice. brake fluid that meets DOT 4 specifiFor street you point. shouldIf use cations for wetuse, boiling the brake meets fluid that meets DOT 4 specififluid DOT 4 specifications, it I f the cations for all wet boiling point. also meets parts of DOT 4, includfluid meets D Opoint. T 4 specifications, boiling Your choice of ita ing wet partsshould o f DOT includalso meets all brake-fluid brand be 4,based on ing boiling point. Your choice of a the wet following requirements: brake-fluid brand should on • Use a fluid that your be carbased m anuthe following requirements: facturer recommends. fluid that of your car manuDon ' a t mix brands fluids. • Use facturer recommends. Violate either of these rules, and Don't mix brands o f fluids. long-term harm may occur to your Violate either For of these rules,some and brake system. instance, long-term your brake fluidsharm maymay reactoccur with torubber brake insystem. instance, seals a brake For system. Over asome long brake fluids may react with rubber period of time , this may cause swelling sealsleakage. i n a brake a long or Thissystem. occurs Over commonly period o f.S.-manufactured time, this may cause swelling when U brake fluid or leakage. is used in anThis olderoccurs foreigncommonly car with when U.S.-manufactured fluid natural-rubber seals . The brake seals swell is used i n an older foreign car and have to be replaced eventuwith ally. natural-rubber seals. The seals swell and have to be replaced eventually.

You wouldn't dare do this with ordinary glycol-based brake fluid; it would remove the There's to paint with You paint. wouldn't darenododanger this with ordinary silicone fluid. Silicone fluiditiswould ideal for cars glycol-based brake fluid; remove that have There's problems with brake-system no danger to paint with the paint. contamination and corrosion. courtesilicone fluid. Silicone fluid isPhoto ideal for cars sy Yankee that have Silicones, problemsInc. with brake-system contamination and corrosion. Photo courtesy Yankee Silicones, Inc.

Consult the factory shop manual or your dealer for brake-fluid recomConsult t h e factory shop manual or mendations. your dealer brake-fluid Brake-fluid for brands contain recomblends mendations. of chemicals, so their properties Brake-fluid change when brands mixed. contain If you blends must of chemicals, s o their properties change brands, flush out the brake change and when mixed. If you system replace all brake fluid.must See change brands, flush out the brake brake Chapter 11 for tips on changing system fluid. and replace a l l brake fluid. See for the tips highest on changing brake Chapter If you 11 want wet boiling fluid. point and a different combination of If you want highest wet changboili~~g properties, youthe might consider point and a different combination of ing to silicone-based brake fluid. Siliproperties, you might consider changcone fluid is required to meet DOT 5 ing to silicone-based specifications. This brake fluid fluid. does Silinot cone fluid is required DOT 5 absorb moisture like toa meet glycol-based. specifications. Thisits fluid does not fluid. Therefore, wet boiling is absorb moisture like a glycol-based much higher. Also, silicone fluid will fluid. Therefore, its wet boiling not damage the paint on your car is if much higher. Also, silicone fluidfluid will brake spilled. But glycol-based not damage h e paint o n your car if makes good tpaint remover on some spilled. But glycol-based brake fluid finishes.

makes good paint remover on s o m e finishes.

A good application for silicone brake fluid is in antique and collector A Brakes good in application silicone cars. these typesforof cars are brake fluid is in to antique and collector never subjected high temperatures cars. Brakes in types oftemperacars are encountered in these racing-high never subjected to high temperatures tures that can cause si licone fl uid to encountered in protection racing-highof the temperacompress' And intertures that can silicone isfluid to nal parts fromcause corrosion most compress! And protection of the interimportant. Silicone brake nuid serves nal parts from corrosion is most this purpose beautifully, because the important.ofSilicone brake serves absence moisture in fluid the system this purposeeliminates beautifully, practically thebecause chance the of absence of moisture in the system dreaded internal corrosion. However, practically chance of for racing, eliminates use only atheglycol-based dreaded internal racing brake fluid. corrosion. However, forSilicone racing, fluid use only glycol-based has abeen tried in racing brake fluid. raci ng, bu tit has a tendency to gi ve a Silicone fluid been tried in spongy pedal afterhasexposure to high racing, but it has tendency to give temperatures. Thisa is due to the slighta spongy pedal after exposure to fluid high compressibility of silicone brake temperatures. This is d u e to t h e slight at high temperature. For ordinary compressibility of silicone brake but fluida street driving, this is not critical, at high temperature, For ordinary racer needs all the brake-system stiffstreethedriving, ness can get.this is not critical, but a racer needs the brake-system stiffyou change Switching toallSilicone-If ness h e can brake get. fluid, you must first to silicone Switching to the Silicone-If change clean all of old fluidyou from the to silicone brake fluid, you must first brake system to get the maximum clean of the fluid from the benefitall of the oldsilicone fluid's brake system maximum properties. The to bestget waythe to accomplish benefit of brake-system the siliconeoverhaul. fluid's this is during properties. T h e best way to accomplish Totally drain and clean out the old this isIfduring brake-system overhaul. you merely bleed out and influid. Totally cleanhave outa mixture the old stall newdrain fluid, and you will fluid. you merely out and of the Iftwo fluids. Thisbleed will work, butinit stall new fluid, you will have a mixture won't be as good as it could be.

of the two This will work, but Keep Outfluids. Contaminants-If youit won't as good as it could don't be use silicone brake be. fluid, do Keep O u t possible Contaminants-If everything to keep water you out don't use silicone brake fluid, do of the brake fluid. Although it's more everything possible to keep water out expensive, always buy brake fluid in of t h e brake more small cans. fluid. KeepAlthough the cansit'sclosed expensive, always buy opened, brake fluid in before using. Once don't small cans. Keep t h e cans closed keep an old can of brake fluid around before using. Once opened, don'tit long. Use it immediately or throw keep an old can of bleed brake some fluid around of the away. Periodically long.fluid. Use This i t immediately or throw it old removes contaminated away. Periodically bleed s o m e ofreuse the fluid from the system. Never old fluid. This removes contaminated dra ined/hi id. fluid from the system. Never reiise hained,fluid.

Howe master cylinder has rubber diaphragm built into lid. This keeps air from contacting and cylinder contaminating brake fluid. Howe master has rubber diaUnfortunately, caplid.must removed to phragm built into This be keeps air from check fluid level, partially defeating advancontacting and contaminating brake fluid. tage of rubber diaphragm. unfortunately, cap must b e removed to check fluid level, partially defeating advantage Of rubber diaphragm.

If you have a choice, always use a master cylinder with a rubber diaIf you inhave choice, always phragm the acap to seal the use fluid.a master cylinder withfrom a rubber This keeps the fluid exposurediato phragm the cap to fluid. air. Mostin moisture in seal brakethefluid is This keeps the fluid from exposure to picked up from air on damp days. All air. Most moisture brake fluid is master cylinders andinreservoirs must picked up from air o n damp days. All be vented to atmosphere, so don't master cylinders plug vent holes. and reservoirs must be Invented to toatmosphere, so don't addition moisture, brake fluid plug can vent be holes. contaminated by other In addition moisture, brake fluid materials. Dirtto can enter the system can be contaminated by other when nuid is added to the reservoir. It materials. can enter system is critical Dirt to keep dirt the from the when fluid added to the reservoir. It system, so isuse extreme care when is critical to keep dirt from the working on your brakes. Usual consystem, s o isuse when tamination by extreme petroleumcare products working o n your brakes. Usual consuch as oil, grease or solvents. Petrotamination is bymix petroleum products leum solvents with brake fluid such can as oil, gre'aserubber or solvents. Petroand damage seals in the leum solvents mix with brake fluid system. Never clean brake-system and can damage rubber Use sealsalcohol, in the components with solvent. system. cleat7 brake-systet77 brake fluidNever or brake-system cleaners. cot7~ponenfs alcohol, Solvents are with too solvenf. difficult Use to wash off, brake fluid or brake-system cleaners. and will contaminate brake fluid.

Solvents are too difficult to wash off, and will contaminate brake fluid.

65

Brake Pedals & Linkages Brake Pedals 8 Linkages

Bird's-eye view of foot-box area of formula car shows pedals, linkages and brake and clutch master cylinders. Dual brake master cylinders with remotely adjustable balance bar is used. Note bumper protecting master cylinders head-on impact. Bird's-eye view of foot-box area of formula carfrom shows pedals, linkages and brake and

clutch master cylinders. Dual brake master cylinders with remotely adjustable balance bar is used. Note bumper protecting master cylinders from head-on impact.

Most road-car pedals are hanging-pivots are above pedal pad-and pedal bracket doubles as a pedals steering-column bracket. Most road-car are hanging-pivots Device nearpedal top of brake pedal a meare above pad-and pedalisbracket chanical switch. doubles brakelight as a steering-column bracket.

Device near top of brake pedal is a mechanical brakelight switch.

66

The brake pedal and linkage transmil force and movement from the The brake driver's footpedal to and the linkage mastertranscymit force and movement from the linder(s). Design and construction of driver's to affect the how master cythese partsfoot greatly a brake l i n d e r ( ~operates ) Design . and how construction system and it feels of to these parts greatly affect how a brake the driver. The brake pedal must be system operates andpart howofit afeels to the most reliable brake the driver. The brake system because failurepedal can must mean bea the most loss reliable part .ofThe a result brake complete of braking system because failure can mean a can be catastrophic. complete loss of braking. The result When building a car, you may want can be catastrophic. to design and fabricate the brake pedal When building a car, want and linkage. These partsyou aremay some of to design and fabricate the brake pedal the components that can be fabricated and linkage. parts This are some of by the home These craftsman. chapter the components that can fabricated describes how pedals and be linkages are by the home chapter designed and craftsman. fabricated This for safe and describes how pedals and linkages are reliable brake operation. The pedal designed and fabricated for safe and and linkage are normally designed as a reliable operation. The pedal part of a brake comp lete brake system. This and linkage are normally designed as a is discussed in Chapter 9.

part of a complete brake system. This is discussed in Chapter 9. BRAKE PEDAL A

brake

pedal

BRAKE PEDAL A brake pedal

is

familiar

to

is familiar

to

&

everyone who has driven a motor vehicle. Take a good look at the pedal everyone has important driven a design motor in a car. who It has vehicle. Take a good look at the pedal features . Good brake pedals have the in a car. It has important design following characteristics: features. Goodbreak brake or pedals have the • Must not permanently following characteristics: bend under the greatest load a driver Must can apply.not break or permanently bend under the greatest driver • Must be stiff and notload flexa during can apply. hard braking. befree stiffofand not flex during • Must Must be excessive friction . hard braking. • Must provide proper leverage at Mustcylinder. be free of excessive friction. master Must provide proper leverage at • Must match requirements of driver master cylinder.cylinder, linkage and and master Must match requirements of driver system. andA brake masterpedal cylinder, and consistslinkage of the arm, system. pad and pivot attachments. The pedal brake pedal consists This of the arm, is A connected to a linkage. linkage pad and pivot attachments. The pedal transmits force and movement to the is connected to aThe linkage. Thiscan linkage master cylinder. linkage be as transmits force and movement the simple as a straight pushrod, ortomore master cylinder. The linkage can be as complex. simple as a straight pushrod, to or bendmore The pedal arm is subjected complex. ing loads from the driver 's foot. It is The pedal arm is subjected to bendusually constructed of steel plate. The ing loads driver's is arm may from havethe holes in itfoot. for Itthe usually constructed of steel plate. The pivots. Often pivot bushings are conit for the arm have steel holes intubes-pivot tainedmay in pivots. Often pivot bushings housings-that are inserted in are the conarm tained in in place steel . A tubes-pivot and welded good pedal housings-that inserted in the arm design will not are have welds completely and welded in place. A good across the arm, particularly atpedal the design have iswelds pivots. will A not weld a completely source of across the arm, riser-at particularlya critical at the weakness-stress pivots. A weld is a source of area of the arm. weakness-stress riser-at a critical A pedal arm is usually straight - the driver's seat. If area the arm. whenofviewed from is usually straight it A has pedal bends arm or curves in it , the arm when viewed from the driver's seat. If tends to twist when the pedal is it has bends or curves it, arm the arm pushed . Twisting in the in pedal can tends movement to twist when is create at thethepadpedal , giving pushed. Twisting the pedal armAlso, can the driver feel ofin sponginess. create movement giving stresses in a pedal at willthe be pad, higher due the driver feel of sponginess. to twisting forces. To overcome Also, these stresses in pedals a pedalwith will bends, be higher due problems, offsets to twisting forces. overcome these or curves must be To fabricated of heavproblems, ier material.pedals with bends, offsets or Acurves fabricated good must pedalbearm should ofbeheavdeier material. signed to take side loads and forward A good be deloads. Side pedal loads arm on a should pedal arm are signed to take side loads and forward most likely to cause failure , because loads.arms Side are loads on alaterally. pedal arm are most weaker Pedals most likely to cause failure, because shou ld be installed so they won't be most weaker loadedarms fromarethe side. laterally. A brake Pedals pedal should be installed so won'tleg.be should be in line with thethey driver's loaded the side. brake pedal Pedalsfrom in most road A cars are made should be in line with the driver's leg. of steel. This gives a pedal the highest

Pedals in most road cars are made of steel. This gives a pedal the highest

Pedal Bracket

Pedal Bracket

Pivot Housing

Master-Cylinder Pushrod

Master-Cylinder Pushrod Pad

Hanging pecial has pivot housing at top of arm. On many pedals, pivot housing is a steel tube welded into a hole in pedal arm. Pivot bushing is inside pivot housing. For rear-mounted master master-cylinder-pushrod pivotOn installs pivot, 70. is a steel tube Hangingcylinder, pecial has pivot housing at top of arm. manyabove pedals, pivotpage housing

welded into a hole in pedal arm. Pivot bushing is inside pivot housing. For rear-mounted master cylinder, master-cylinder-pushrod pivot installs above pivot, page 70.

stiffness and strength of any low-cost material. Older cars often used steel stiffness strengthbut of modern any low-cost forgings and for pedals, cars material. Older cars often used steel steel use parts cut or stamped from forgings for cars pedals, but modern cars plate. Race sometimes use lightuse parts cut or stamped from steel weight materials such as aluminum or plate. Race cars sometimes use lighttitanium. Consequently, race-car weight materials such as aluminum or pedals are expensive when compared titanium. Consequently, race-car to those for road cars. However, steel pedals arethe expensive whenItscompared will offer best results. stiffness to for road cars. However, is as high assteel any for those a given weight will the bestand results. stiffness it isItseasier to otheroffer material, for a givenDesigning weight is as as any fabricate. an high aluminum other material, and itbecause is easier to be difficult of its pedal can fabricate. Designing an aluminum low stiffness. pedal difficult because its be of rigid. A can pedalbe arm must low stiffness. Therefore, it usually has a deep cross A pedal must has be arigid. section. A roadarm car usually flatTherefore, has a deep cross cross plate or itanusually open-channel section. Abutroad car usually has ause flat-a section, a race cars often plate or an open-channel cross tube. Tubular pedals are lighter for a section, but a race cars often useex-a given stiffness. However, they are tube. Tubular pedals toaremass lighter for a pensive and difficult produce. given stiffness. However, they are exWith a tubular pedal, a thin-wall tube pensive and difficult to mass produce. can be used and still have enough With a tubular pedal, a thin-wall tube stiffness. canA be used stillbehave enough pad and should shaped to fit pedal stiffness. the foot. A tiny pad is hard to push A pedal padand should to off fit with comfort your be footshaped can slip A tiny padpad is hard to push the foot. is about shoe easily. A good pedal with comfort and yourallows. foot can off width; wider if space A slip rubber easily. A good pedal pad is about shoe pad is used on road cars for aesthetics, A rubber width; wider if space comfort and grip. Forallows. race cars, a texpad used on cars for is used for aesthetics, maximum turedis metal padroad comfort andisgrip. For race cars, a texespecially important in grip. This tured metal pad is used for maximum grip. This is especially important in

Small pedal pads are in a Formula Ford road-racing car. These little single-seat racers have pads barelyare enough room for Ford the Small pedal in a Formula driver's feet,car. making small pedal pads a road-racing These little single-seat must. surfaces are made racersNonskid have barely enough roomfrom for exthe panded pads.pedal pads a driver's metal feet, welded makingtosmall

must. Nonskid surfaces are made from expanded metal welded t o pads.

open race cars that run in the rain. Some race-car pedals have an adopen racepad, cars that run in the justable adjustable to rain. suit the Some race-car pedals have an adare driver. Seats in many race cars justable pad, adjustable adjustable pedal to suit pads the fixed, so driver. Seats teo in many race cars are com pensa fixed, so adjustable pedal With adjustable pads, you can pads vary compensate. the distance between the steering Withand adjustable pads,This youwill canaffect vary wheel brake pedal. the distance between the steering arm position when the driver is seated wheel This adjustable will affect in the and car. brake A racepedal. car with arm position when the driver is seated pedal pads and seat can be made to in the A race carperfectly. with adjustable sui t thecar. driver nearly pedal pads and seat can be made to suit the driver nearly perfectly.

Room and weight are not a problem in this racing stock car, allowing big and sturdy pedal Such pedals not fit in a Room pads. and weight are not would a problem in this cramped Grand Prix-car cockpit. racing stock car, allowing big and sturdy

pedal pads. Such pedals would not fit in a cramped Grand ~ r i x - c acockpit. r

Pedal pad is adjusted by releasing jam nut and screwing pad in and out. Pad is welded to a bolt, threads a tapped Pedal padwhich is adjusted byinto releasing jamtube nut at top of pedalpad arm. Moreout. than l-in. of adand screwing in and Pad is welded justment movinginto driver's seat. tube to a bolt, requires which threads a tapped at top of pedal arm. More than 1 -in. of ad-

justment requires moving driver's If heel-and-roe brakeandseat. accel-

erator-pedal operation is desired, the heel-and-toe and acceltwoIf pedals should brakebe positioned no erator-pedal is desired, the I-I/2-in. apa rt laterally. more than operation two pedals should be positioned be adjus ted no so Also, the pedals should more than 1-112-in. apart laterally. that during hard braking , the brake Also, pedals adjusted so to should about be 1/4-in. above pedal the travels that during hard braking, the brake the accelerator pedal. pedal travels to about 1/4-in. above the accelerator pedal. PEDAL FORCES The two forces a pedal designer PEDAL FORCES must consider are: twoforce forces n everdesigner be ap• The Highest thata capedal must consider are: Highest force that can ever be ap67

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4

Once wheels are locked, driver's strength is the only thing limiting brake-pedal force. As fear increases, the harder he pushes. This condition represents the maximum force that . Once can bewheels appliedare to a brake driver's system. strength Brake-pedal force maximum-deceleration, conlocked, is the onlyduring thing alimiting brake-pedal force. As trolled stop is much fear increases, the lower. harder he pushes. This condition represents the maximum force that

can be applied to a brake system. Brake-pedal force during a maximum-deceleration, controlled stop is much lower.

plied to a pedal. • Force normally applied in a hard pliedattomaximum a pedal. deceleration. stop Force hard These normally two forcesapplied are not inthea same. stop at maximum Maximum forcedeceleration. is considerably Thesethan twothe forces not theapplied same. higher force are normally Maximum force is considerably during a hard stop. To keep the terms higher thanthetheforce forcenormally normally applied applied separate, during aahard To iskeep the terms during hardstop. stop called pedal separate, normally applied effort. Thistheis force the force applied to a during hard stopwhen is called pedal pedal bya the driver he tries to is the force applied In to aa efforl. atThis stop maximum deceleration. pedal by pedal the driver he tries to race car, effort when is applied by the stop at almost maximum In a driver everydeceleration. time he brakes race car,This pedalis effort applied by thea the car. rarelyisthe case with driver almost every time he brakes road car. theDuring car. This rarely the case an isemergency, the with drivera road car.stop the car at maximum decelshould During an the emergency, theverge driver eration with tires on the of should stop the car at maximum decellockup. Often, though, a driver in eration theabout tires on the vergethe of trouble with forgets controlling lockup. Often,he though, a driver in car. Instead, panics and jams on trouble forgets about controlling the the brakes as hard as he can and locks car. Instead,Often he panics and jams and on the wheels. he loses control the brakes hard as heiscan and maxilocks skids. This as type of stop where the losesoccurs. control The and mumwheels. force Often on a he pedal skids. This type of stop is where maxipedal and linkage must be designed on ora pedal occurs. bend The mum not toforce break permanently pedal and condition. linkage must be designed under this not break or permanently bend Pedalto Effort-A high-performance under this condition. brake system usually is designed for Pedal 75-lb Effortpedal -A effort high-performance about at maximum brake system This usually is designed for deceleration. feels OK to most about pedal effort maximum people.75-lb Anyone personat can easily deceleration. This his feels apply 75 lb with leg.OK If to youmost are people. Any one person can designing a truck or race car, youeasily may Ib with his leg. you are apply wish to75use a higher pedalIf effort. A designing a truck you may 100-lb pedal effortoris race still car, manageable, wish use like a higher A but it tofeels a hardpedal push.effort. I don't 100-lb pedal effort is still manageable, recommend usin!1 more than 100 lb. I don't but it there feels would like a hard Then not bepush. any reserve

recommend using more than 100 lb. Then there would not be any reserve

68

force left for brake fade or other system failures . force for brake other Mostleftpassenger carsfade haveor powersystem failures. assisted brakes. With power assist, Most passenger powerpedal effort is usuallycars less have than 50 lb. assisted brakes. With power Maximum Pedal Force-A assist, heavy pedal usuallypush less with than 50 Ib. personeffort can iseasily a force Maximum Pedal Force-A heavy greater than his weight-about 300 Ib person canman. easilyIf push with aquickly force for a large he stomps greater than his weight-about 300 Ib on the pedal, the effect of the sudden for a large man. If he stomps force further increases stress quickly on the on the Engineers pedal, the know effectthat of the pedal. if asudden load is force further increases stress applied quickly, stress on a on partthe is pedal. Engineers know pedals that if aare loaddeis doubled. Most brake applied toquickly, stressthe on maximum a part is signed take twice doubled. brake pedals areI use de; force that Most a strong leg can apply. twice the maximum signed to take 600 Ib for designing pedals. force a strong legpedal can apply. I use Safetythat Factor-The should be 600 Ib for designing pedals. designed to withstand a force much Safety than Factor-The pedal force should be higher the maximum . The designed to withstand a force much ratio of the force required to break a higher the maximum force. The part to than the maximum applied load is ratio ofthe thesafety forcefactor. required to abreak called I use safetya part toofthe maximum applied load factor 3 on critical parts such as isa safe@ factor. I use a safety called the brake pedal. This means the part is defactor of on critical parts suchthree as a signed to 3break at a load at least brake pedal. This means the applied part is detimes the maximum force to signed to break at a loadthe at least three the part. Therefore, breaking times theformaximum forceshould applied strength a brake pedal be to at the part. Therefore, the breaking least 1800 lb, or 3 X 600 lb . strength a braketo pedal be at If you for wanted test should your brakeleast 1800 Ib, or 3 X 600 Ib. pedal design, apply an 1800-lb force youpadwanted to test your onIfthe in a direction in linebrakewith pedalforce design, the that apply wouldanbe 1800-lb applied force by a on the padfoot. in a Ifdirection in line with person's the pedal doesn't the force would be applied by a break, thethat safety factor is adequate. person's foot. If the pedal doesn't You may bend the pedal doing such a break,never the safety factor inis aadequate. testuse a pedal car after You may the strength pedal doing such a testing its bend breaking . test-never use a pedal in a car after The master-cylinder pushrod must testing its breaking strength. withstand the maximum pedal force

The master-cylinder pushrod must withstand the maximum pedal force

Bird's-eye view of formula-car pedal box: Note that pedal pad is not centered on pedal arm. view This oftwists pedal pedal arm when Bird's-eye formula-car box: driver pushes on pad. tubular arm Note that pedal pad Although is not centered on can withstand thistwists twisting load,arm pedal aspedal arm. This pedal when semblypushes would on be pad. stronger if padtubular and pedal driver Although arm arm were centered. can withstand this twisting load, pedal as-

sembly would be stronger if pad and pedal times thecentered. pedal ratio. Pedal ratio can be arm were

obtained by dividing pedal travel at times the pad pedalbyratio. Pedaltravel. ratio can be the foot pushrod Pedal obtained by dividing pedal travel at ratio is discussed in more detail on the the foot padpage by .pushrod Pedal following Also, travel. a push rod ratio is discussed more detail should always be in straight. One on thatthe is following page. Also, a pushrod straight is many times stronger than a should be straight. One that is bent or always offset rod. straight is many totimes stronger In addition normal load,than thea bent offset pedalormust berod. able to resist some side In addition normal load, the load. A driver'sto foot is not always pedal must be able to resist some side aligned with the pedal pad. The worst load. occurs A driver's not always case wherefoot the isdriver's foot aligned with the pad.This The puts worsta hangs halfway offpedal the pad. case force occurs the arm. driver's foot side intowhere the pedal I recomhangs halfway off the pad. This puts mend using a side load of 200 lb ona side force pad intointhe pedal arm. I recomthe pedal addition to the 600-lb mend using side of 200 Ib on forward load.a If youload apply the safety the pedal pad in addition to the 600-lb factor of of 3, the pedal should not forward load. Ifwith youa apply break if tested 600-lbthe sidesafety load factortheof pad. of 3, Note: the pedal not on The should side load break ifbetested withat athe 600-lb load should applied sameside time as othe n forward the pad. Note: The side load load. should be applied the same timeyou as All this suggestsat that perhaps the forward should leaveload. brake-pedal design to an All this Ifsuggests engineer. you arethat notperhaps trainedyou in should leave brake-pedal design to an stress analysis, a mistake here could engineer. If option you areis not trained in be fatal. An to use a pedal stress analysis, a mistake could that fits from another car. here All pedals be fatal. An using optionsimilar is to use a pedal are designed techniques. that fits from another car. All Safety factors may vary, but the pedals maxiare designed techniques. mum force ausing pedalsimilar can withstand is Safety the factors may but the maxiabout same forvary, all cars. Be aware mum force from a pedal cancarwithstand is that a pedal a road will probaabout the same for all cars. Be aware bly be stronger than a race-car pedal. that a pedal fromdesigners a road cartry willtoprobaMany race-car save

bly be stronger than a race-car pedal. Many race-car designers try to save

Bad pedal design on homemade race car has pedal arm off-center to pad and pivot housing. pushed on, twistrace of arm Bad pedalWhen design on homemade car causes excessive flexibility and has pedal arm off-center to pad andhigher pivot stresses. If arm were moved right,ofpedal housing. When pushed on, to twist arm would beexcessive stiffer and stronger. causes flexibility and higher stresses. If arm were moved to right, pedal would be stiffer and stronger.

weight at the expense of strength. If you insist on designing your own weight at the follow expense of strength. brake pedal, these rules: on designing Doyou not insist weld across a pedal your arm. own • If brake pedal, rules: when • Make the follow pedal these arm straight D o not weldtheacross a pedal viewed from driver's seat.arm. Make the pedal arm straight when • Use steel, not aluminum or other viewedalloys. from the driver's light Steel givesseat. maximum Use steel, not of aluminum or Weldother stiffness and ease fabrication. light alloys. Steel gives maximum ing drastically weakens aluminum. stiffness andtheease of fabrication. Weld• Position pedal arm in the center ingthe drastically aluminum. of pad - notweakens off to one side.

Position the pedal arm in the center of the pad-not off to one side. PEDAL PIVOTS Pivots in brake pedals should have

PEDAL plastic orPIVOTS bronze bushings to reduce Pivots in brake bushings pedals should have friction. Plastic are often plastic or road bronzecars bushings to reduce used on to reduce cost; friction. Plastic bushings often bronze bushings are found are on some used on road cars to reduce race cars. The best pedal pivots cost; have bronze bushings are found o n plastic some Most provision for lubrication. race cars.are T hdesigned e best pedal pivots withhave bushings to operate provision for lubrication. Most plastic out lubrication, but this does not bushings aremaximum designed durability. to operate withalways give outAvoid lubrication. but that this use doesunlunot pedal pivots always maximum durability. bricatedgive clevis pins or bolts. Some Avoid pedalhave pivots unlubrake pedals beenthat so use designed. bricated clevis pins or bolts. S o mofe They work for a while, but the lack brake pedals havearea been designed. adequate bearing andsolubrication They for athe while, buttothe lackout of usuallywork causes pivot wear adequate bearing area and lubrication rapidly. Then the pedal gets loose and usually causes theextra pivot pedal to wear out sloppy, requiring moverapidly. h e n up thethe pedal loose and ment to Ttake slop.gets Pedal movesloppy, ment is requiring a valuable extra item. pedal Don't movewaste ment to take up the slop. Pedal moveit with potentially sloppy pivots. ment is a valuable item. Don't waste it with potentially sloppy pivots.

Spherical bearings on master-cylinder pushrods minimize friction and wear. Neal Products pedal uses a balance bar with special spherical bearing at each end. Balls in spherical bearings are pinned to on allow motion in onlypushrods one direction. Ordinary would Spherical bearings master-cylinder minimize frictionspherical and wear.bearings Neal Products allow ends to cock, with potentially disastrous results. pedal rod uses a balance bar with special spherical bearing at each end. Balls in spherical bearings are pinned to allow motion in only one direction. Ordinary spherical bearings would allow rod ends to cock, with potentially disastrous results.

If you have a car with sloppy or unbushed pedal pivots, consider modifyyou have a car have with sloppy or un-a If you to enlarge ingIf them. bushed pedal pivots, consider modifyhole to install a bushing, make sure ing them. you have to enlarge a you don't If weaken a critical area. If hole are to install a bushing, you uncertain, leave it make alone.sure Or, you weakendoa acritical area. If have don't an engineer stress analysis you are uncertain, leave it alone. Or, of the modification. If you don't bush havepivots, an engineer a stress them analysis the at leastdolubricate at of the modification. If youwear. don't bush regular intervals to reduce

the pivots, at least lubricate them at regular PEDALintervals RATIO to reduce wear.

The force required on the masterPEDAL piston RATIOis usually much higher cylinder T h e force required o n the masterthan the pedal effort supplied by the cylinder piston is usually muchact higher driver. Thus, the pedal must as a than pedal effort supplied by the the force supplied by lever the to increase driver. Thus, The the pedal must act the driver. leverage of as thea lever to increase the force pedal-pedal rario-is alsosupplied known by as the driver. T h e leverage of the mechanical advantage. Pedal ratio for pedal-pedal as manual brakesratio-is is aboutalso 5 toknown 1; power mechanical advantage. Pedal pedal ratios are about 3 to 1. ratio for 1; powera manual is about If youbrakes plan to design 5 orto modify 3 to 1. pedal ratios are about brake system, you need to determine you plan design modify theIf pedal ratio.toThere areorthree waysa brake you need determine to do system, this. Choose the to method that the pedal There works best ratio. for you. Theyare are:three ways to do this. forces. Choose the method that • Measure works best for you. They are: • Measure movements. Measure forces. • Measure brake pedal and linkage Measure movements. geometry. MeasureForces-If brake pedal and measure linkage Measure you can geometry. the force on the pedal pad and the M e a s u r e Forces-If simultaneous force you on can the measure masterthe force o n the pedal pad cylinder piston, the pedal ratioand can the be

simultaneous force o n the mastercylinder piston, the pedal ratio can be

Typical road-car pedal design; pivot bolt and bushing are removed. Plastic bushings last longer if greased occasionally. Typical road-car pedal design; pivot bolt and bushing are removed. Plastic bushings last longer if greased occasionally.

calculated from this simple formula:

calculated from F this simple formula:

Pedal ratio

=

ｾ＠

Fpp F M FMC Force on~ master cylinder in Pedal=ratio =pounds FPP FMc= =Force Force on master Fpp on pedal pad in cylinder pounds in

pounds

Forces are measured in inpounds; Fpp= Force on pedal pad pounds the pedal ratio is just a number. If you Forcespush are on measured pounds; could the pedalinwith a scalethe or pedal ratio isto just a number. you instrument measure force,If you could pushsimultaneously o n the pedal with ameasure scale or could instrument to measure force, you hydraulic-system pressure. If you could measure know the simultaneously master-cylinder-piston area, hydraulic-system pressure.into If force you pressure can be converted know the master-cylinder-piston area, on the piston.

pressure can be converted into force o n the piston. 69

FMc*q ｾ＠

i

-

ｾ＠

Vacuum Hose Intake Manifol

-Brake

Pedal

Valve Rod

Force

Piston Area = 1 sq in . Hydraulic-Cylinder Force & Pressure Piston Area = 1 sq in. \:' 10-psi Vacuum Hydraulic-Cylinder Force & Pressure BoosterSaO-lb. \ Diaphragm Force Area = BoosterAddedb.to 500-1 Diaphragm 50 sq in. Master I Force Area = Cylinder ' I Added to 50 sq in.

JjjT _--__..... ｾｉ＠

Typical vacuum-booster setup : Intake manifold supplies vacuum to booster. Brake pedal pushes directly on booster-valve rod, which controls force booster applies to master cylinder. If vacuum supply dropsIntake to zero or booster fails,vacuum a mechanical linkage operates Typical vacuum-booster setup: manifold supplies to booster. Brake pedal master-cylinder by pushing harder on pedal. Effort increases pushes directly piston on booster-valve rod, which controls force boostersignificantly applies t o without master boost. Drawing courtesy Bendix Corporation. cylinder. If vacuum supply drops to zero or booster fails, a mechanical linkage operates

master-cylinder piston by pushing harder on pedal. Effort increases significantly without boost. Drawing courtesy Bendix Corporation. Diaphragm

Booster Housing ｾ＠

Vacuum Line

_ _ OpenTo Atmosphere

1O-psi Vacuum Zero-psi Atmospheric Pressure

Zero-psi Atmospheric Piston F

=

Force on Master Cylinder Piston

Pressure on diaphragm is difference between vacuum and atmospheric pressures. Because F = Force on Master Cylinder Piston vacuum is below atmospheric pressure, it is given a minus value. In this example -10 psi is in vacuumonside of chamber and 0 pSi-atmospheric in other side. Vacuum of Pressure diaphragm is difference between vacuumpressure-is and atmospheric pressures. Because -10 psi is vacuum below atmospheric i t is given a minus value. Inbut thisresulting exampleforce -10 psi is gives same force as 1pressure, O-psi pressure above atmospheric, is in oPPosite in vacuumdirection. side of chamber and 0 psi-atmospheric pressure-is in other side. Vacuum of

-10 psi gives same force as 10-psi pressure above atmospheric, but resulting force is in opposite direction.

VACUUM-BOOSTER TYPES Most power-brake systems use a VACUUM-BOOSTER TYPES booster operated by vacuum from the Most power-brake systems use a intake manifold of a naturally aspiratbooster operated by vacuum from the ed engine. Because manifold vacuum intake manifold of a naturally aspiratis highest-pressure is lowest-when ed Because manifold vacuum the engine. driver lifts his foot off the throttle, is highestpressure is lowest-when vacuum in the booster is maximum as the driver liftsare his foot off theThis, throttle, the brakes applied. of vacuum isindifferent the booster maximum as course, for ais supercharged the brakes applied. This,usuof engine, whereare manifold pressure course, is different for a supercharged ally is greater than ambient air engine, pressure.where manifold pressure usually greater air Theis extra forcethan on ambient the masterpressure. cylinder piston is provided by a large The inside extra the force on booster. the masterpiston power In a cylinder piston isthis provided a largea vacuum booster, piston by is called piston inside theseepower booster.ofInthea diaphragm. You the outside vacuum booster, this piston is called cylinder-chamber- when you looka

diaphragm. You see the outside of the cylinder-chamberwhen you look 78

at a vacuum booster. It's the large, round object that looks like a tank. at Vacuum a vacuumboosters booster. have It's thea large, large round object that looks like a tank. diameter because vacuum exerts a Vacuum boosters have a large Actually, the very low "pressure." diameter because vacuum exerts outside air exerts pressure; vacuuma very low it."pressure." the removes Ambient Actually, air pressure outside air exerts pressure; vacuum (14.7 psi) is one one side of the diaremoves it. engine Ambient air pressure phragm and manifold vacuum (14.7 psi) is one one side of the diathe other. Air pressure is reduced on phragm and side engine manifold vacuum the vacuum by engine vacuum. A the other. Air pressure is reduced on perfect vacuum on one side of the dithe vacuum side abymaximum engine vacuum. A aphragm allows pressure perfect vacuum on one side of the diof only 14.7 psi. This is a pelfec! aphragm allows maximum pressure vacuum. In real alife, it is never that of only 14.7 psi. This is a pellfect high. Compared to about lOOO-psi vacuum. real life, is never that maximumInpressure in ait brake hydrauhigh. Compared to about pressure 1000-psi lic system, the vacuum-boost maximum a brake hydrauis about 10 pressure psi. The in result is the large-

lic system, the vacuum-boost pressure is about 10 psi. The result is the large-

Master Cylinder

I,ll

II

II

---

Vacuum- Booster Force & Pressure

VacuumBooster operates Force & Pressure Master cylinder at about 1 OOO-psi maximum hydraulic pressure. Because at Master vacuum cylinderdiaphragm operates operates at about about 10-psi maximum pressure, booster 1000-psi maximum hydraulic pressure. Bediaphragm is 5 to 10 times operates diameter of cause vacuum diaphragm at master-cylinder piston pressure, to give required about 10-psi maximum booster area. diaphragm is 5 to 1 0 times diameter of master-cylinder piston t o give required diameter cylinder. Remember, total area. force equals pressure multiplied by diameter Remember, total the area ofcylinder. the piston - diaphragm in force equals pressure multiplied by the pressure is hythis case-whether the areaorof the piston-diaphragm in draulic a vacuum . this casewhether the pressure is hyThe pedal linkage is connected to a draulic or a vacuum. mechanical linkage that pushes on the The pedal linkage connected to a master cylinder. The isdriver can push mechanical-linkage that pushes on the master cylinder the same as inthea master The driver can push normal cylinder. brake system. However, the the the same asfrom in a pedalmaster effort cylinder is high without assist normal brakeThe system. the the booster. boosterHowever, merely adds pedal effort is high without assist from force to the master-cylinder pushrod the booster. The pushes boosteron merely adds when the driver the pedal. forcetotal to the master-cylinder pushrod The force on the master-cylinder when driver on pedal the pedal. piston the is the forcepushes from the plus The total force on the master-cylinder the booster force. piston the force fromlook the pedal plusa Let'sis take a closer at how the booster force.works . To restate, a vacuum boost Let's take a closer look atforce how bya booster diaphragm supplies vacuum boost works. To restate, having a vacuum on one side of the di-a booster supplies force on by aphragm diaphragm and atmospheric pressure having a vacuum on one sidewhenever of the dithe other. A vacuum exists aphragm on pressure and in atmospheric a gas falls pressure below atthe other. A vacuum exists whenever mospheric pressure. Most pressure pressure a ingasthefalls below , atgages read inzero atmosphere so mospheric pressure. vacuum gagesMost are pressure used to special gages read zero in the atmosphere, so measure pressure below one special vacuum gages are used atmosphere. If most of the air to is measure one pumped out pressure of a cylinder,below atmospheric atmosphere. the on air the is pressure triesIfto most push of inward pumped out of a cylinder, atmospheric outside of the cylinder. There is a pressure tries to push inward on the lower pressure-vacuum-inside the outside of themain cylinder. There is a cylinder. The parts of a simple lower the vacuumpressure-vacuum-inside booster are the power chamber

cylinder. The main parts of a simple vacuum booster are the power chamber

ber is the diaphragm and its housing. They supply the force. The control valve lets air or vacuum into the power chamber. and the control valve. The power chamAir-Suspended Boosters early ber is the diaphragm and itsAll housing. boosters operated under no load with They supply the force. The control air on lets both air sidesor ofvacuum the diaphragm at valve into the one atmosphere pressure. When the power chamber. brakes were applied, a valve between Air-Suspended Boosters - All early the booster and intake manifold was boosters operated under no load with opened. Air was pumped from one air on both sides of the diaphragm at side of the diaphragm. This type of one atmosphere pressure. When the booster is called an air-suspended brakes were applied, a valve between booster. That means there is air on the booster and intake manifold was both sides of the diaphragm when it opened . Air was pumped from one has no force on it. side of the diaphragm . This type of Vacuum-Suspended Booster-The booster is cailed an air-suspended more modern type of vacuum booster booster. That means there is air on is called vacuum suspended. It has a both sides of the diaphragm when it vacuum on both sides of the diahas no force on it. phragm when there is no force on it. Vacuum-Suspended Booster-The Atmospheric air is let into the power more modern type of vacuum booster chamber on one side of the diaphragm is called vacuum suspended. It has a when the brakes are applied. It is vacuum on both sides of the diaeasier to let air into a vacuum than it phragm when there is no force on it. is to pump air out-particularly when Atmospheric air is let into the power it must be done quickly. Because chamber on one side of the diaphragm vacuum is an absence of ail; air naturalwhen the brakes are applied. It is ly flows into the vacuum when the easier to let air into a vacuum than it valve is opened. Also, the vacuumis to pump air out-particularly when suspended booster is more fail-safe it must be done quickly. Because than an air-suspended booster. That's vacuum is an absence of ail; air naturalanother reason it is popular today. ly flows into the vacuum when the Tandem Booster-Most vacuum valve is opened. Also, the vacuumboosters have one diaphragm in the suspended booster is more fail-safe power chamber. If a large force is rethan an air-suspended booster. That's quired from the booster, cylinder another reason it is popular today. diameter must be large. To make a Tandem Booster-Most more compact booster, some vacuum use two boosters have one diaphragm in the diaphragms. This type of booster is power chamber. If a large force is recalled a tandem booster: The diaquired from the booster, cylinder phragms are mounted in front of each diameter must be large. To make a other in the power chamber, as are more compact booster, some use two the pistons in a tandem master diaphragms. This type of booster is cylinder. They each provide part of called a tandem booster. The diathe booster force. phragms are mounted in front of each Brake-Booster Operation-There are other in the power chamber, as are three basic vacuum-booster operating the pistons in a tandem master conditions: cylinder. They each provide part of Brakes released. the booster force. Brake being applied. Brake- Booster Operation - There are Brakes holding at constant force. three basic vacuum-booster operating The control valve is operating difconditions: ferently each of these conditions. • Brakes for released. operation is shown in •Control-valve Brake being applied. drawing, pageat80. holding constant force. •the Brakes The power chamber of a vacuumThe control valve is operating difsuspended booster is divided into a ferently for each of these conditions. front chamber and a rear chamber by Control-valve operation is shown in the diaphragm. There is always the drawing, page 80. vacuum applied to the front chamber. The power chamber of a vacuumThe vacuum line contains a check

suspended booster is divided into a front chamber and a rear chamber by the diaphragm. There is always vacuum applied to the front chamber. The vacuum line contains a check

Vacuum In Front of Diaphragm

Air to Rear

Hydraulic

Hydraulic Pistons Move Forwar I I Pushrod Typical vacuum-suspended booster: Diaphragm acts like a piston. When brakes are r: ":; -:·.1 Vacuum applied, air is admitted t o chamber behind diaphragm, applying force to master-cylinder ".'·:·'1 Air Corporation. pushrod. Drawing courtesy Bendix

I Typical vacuum-suspended booster: Diaphragm acts like a piston. When brakes are applied, air is admitted to chamber behind diaphragm, applying force to master-cylinder .agrns and pushrod. Drawing courtesy Bendix Corporation. Move Forw

Diaphragms and Plates Move Forward

~ l i Pistons c Move Forward Vacuum Air

I

I

Vacuum in Front of Each Diaphragm-Air to Rear of Each Diaphragm

1::::;...::1Vacuum

Bendix tandem-diaphragm Master-Vac booster in applied position: Vacuum acts on each of [':::-;:::-:1Airbooster force. Unit is used where high force is required and t w o diaphragms, doubling space is limited. Drawing courtesy Bendix Corporation. Vacuum in Front of Each Diaphragm-Air to Rear of Each Diaphragm

-

Bendix tandem-diaphragm Master-Vac booster Vacuum acts on each of Front Shell 3vRear in applied position: Shell two diaphragms, doubling booster force. Unit is used where high force is required and Vacuum Check Valve Bendix Corporation. space is limited . Drawing courtesy

Reaction Disc

Vacuum Check Valve - - - 1

/

W

V

V

-

\ Control Vallie Rod Val

Hydraulic Pushrod

.agm Return Spring Diaphr Master Cylinder Power Section

ｾｲｊｴ

Plate ｜＠ Valve Rod

I

I

Cross-section of Master-Vac booster with working parts indicated. Control valve admits Diaphragm Plate air into chamber behind diaphragm. Valve rod is moved when driver pushes on brake pedal. Drawing courtesy Bendix Corporation.

Cross-section of Master- Vac booster with working parts indicated. Control valve admits air into chamber behind diaphragm. Valve rod is moved when driver pushes on brake pedal. Drawing courtesy Bendix Corporation.

79

I

I

Atmospheric Port closed

'i-

Atmospheric Air

Valve Rod (Retracted) (Retracted)

Diaphragm 3 (Retracted)

L ~ e aShell l Vacuum Released Position Atmospheric Port Open

Atomspheric Air

Valve Rod Rod (Forward) (Forward)

-

\

Diaphragm--' (Forward) ~.

~

lI'lf-'fl,,·'1l

Rear Shell

-vacuum

port closed

Atmospheric Air Applied Position

Atmospheric Port Closed

Atmospheric

Valve Rod (Forward)

Diaphragm (Forward) (Forward)

\

'vacuum Port Closed Atmospheric Air (Trapped) Holding Position

Vacuum-booster control-valve operation shown in simplified form: Rear shellencloses rear chamber of booster and mounts booster-and-master-cylinder assembly to fire wall. wall, Parts move relative to each other. Valve rod rod moves when driver steps on pedal. pedal. Diaphragm Diaphragm moves moves when acted on by atmospheric air pressure and vacuum.

80

valve to prevent vacuum loss in booster when rnnti~folbklpress~rre rises above boosler pressure-or manifold vacuum booster presslrre-or drops below booster vacuum. A check valve opens to allow air to flow flow from bu t closes when ai airr tries to booster, but flow into the booster. booster, With bbrakes r a k e s released, control valve opens a vacuum port that connects front and rear cham bel's. Preschambers. sure on o n both sides of the diaphragm is ized with the brakes released. equalized Both chambers contain a vacuum as running. long as the engine is running. With brakes applied, control valve moves forward. This shuts the vacuum port between front frolit and rear chambers and opens the atmospheric port. Air flows into rear chamber through the t h e atmospheric port, raising The pressure against the diaphragm. T he diaphragm is pushed forward by the air pressure on o n its rear side. The T h e diaphragm then pushes on o n tthe h e mastercylinder pushrod and adds to the force ver. being supplied by the t h e dri driver. If the brake pedal is applied without moving, forces forces on o n the control valve shut both the atmospheric port and vacuum port. This maintains a constant force on o n the master-cylinder pushrod. IIff tthe h e brake pedal is pushed harder, atmospheric port is opened again and additional force is applied by the booster. Wirh With brakes /.elensed, vacuum port is opened: Booster force and assist disappear, disappear. Booster Spring-Boosters Spring-Boosters often are fitted with springs to give the driver the t h e correct amount of feel. feel. It is important that pedal effort not be too low. low. This makes the brakes too sensitive_ sensitive. For the correct amount of feel, pedal effort should increase with pedal travel. As the spring is compressed, pedal effort increases. HYDRAULIC B O O S T E R Some S o m e brake boosters use hydraulics rather than vacuum. Fluid is pressurized by the t h e ppump u m p that also supplies the power-steering system. A hydraulic brake booster is used on o n cars that have a poor source of vacuum from the manifold, t h e intake manifold. Not only does a su supercharged engine eliminate the t h e manifold as a source of vacuum, many newer cars are are equipped with emission controls and vacuum-operated accessories that reduce manifold vacuum, vacuum. On such

cars, hydraulic boosters are more practical, particularly if the car is also

-

Accumulator Port

(j)

-

E- 1500

Pedal Rod

Accumulator Port

.ｾ＠(I]

Pressure Port

:::J

(j) _a 1500(j)

With power Ass'lst

?

OJ

tl: 1000 ,g0F :::J C1l 1000.-0 V)

;

Booster-Runout with power A s Point s i s t

f32

500

Booster-Runout Point

2

500-

u

/Output Pushrod /

ＰｾＭＲＴＶＸＱ＠

0

20

40

Pedal60 Effort (lb) 80

100

Output Pushrod

120

Pedalon Effort (Ib)effort. Runout pOint Curves show effect of power assist pedal is where power booster supplies maximum possible force. If pedal effort isshow higher thanof50 Ib, brake-fluid pressure the Curves effect power assist on pedal effort.increases Runout point same as itpower wouldbooster withoutsupplies power assist-curve with power is is where maximum possible force.assist If pedal parallel non-power-assist past runout point.increases Runout point effort istohigher than 50 Ib, curve brake-fluid pressure the variesas according to eachpower car. Boost force is with limited by available same it would without assist-curve power assist is vacuum tor power-steering-pump pressure. parallel o non-power-assist curve past runout point. Runout point varies according t o each car. Boost force is limited by available vacuum or power-steering-pump pressure. equipped with power steering. And, Power-Steering Gear

there's the advantage of fitting the

equipped hydraulic with powerbooster steering.into And,a smaller there's the advantage of fitting the crowded engine compartment. smaller hydraulic booster into a Like the vacuum booster, hydraulic crowded compartment. booster isengine located between the brakeLike linkage the vacuum pedal and booster, master hydraulic cylinder. booster is located between the brakeThe boost piston has hydraulic prespedal behind linkageit and master sure to add forcecylinder. to the The boost pistonpushrod. has hydraulic presmaster-cylinder In the event sure behind it to the adddriver forcecantopush the of booster failure, master-cylinder pushrod. In the event on t he master-cylinder piston just like driverHowever, can push aof booster normal failure, brake the system. on theeffort master-cylinder piston justto like pedal is much higher due the alownormal brake system. However, pedal ratio. pedal effort is much higherparts dueare: to the Basic hydraulicbooster low pedal ratio. • Boost piston. Basic hydraulic-booster parts are: • Sliding spool valve, which regulates Boost pressure. piston. braking valve, regulates • Sliding Lever spool system to which operate spool braking valve. pressure. system tosystem. operate spool • Lever Reserve-pressure valve. The boost piston operates much Reserve-pressure like any hydraulic system. piston. Because The boost piston operates much power-steering hydraulic pressure is like any hydraulic Because much higher than piston. the "pressure" power-steering hydraulicthe pressure available from vacuum, piston is is much higher than the "pressure" much smaller than a vacuum-booster available from the ispiston is diaphragm. The vacuum, boost piston located much smaller than a vacuum-booster between the rod from the brake pedal diaphragm. The boost piston ispushrod. located and the master-cylinder between the rod from the brake When the brakes are applied,pedal the and thethemaster-cylinder pushrod. lever on input rod slides the valve When the brakes are high-pressure applied, the to a position that allows lever on the input rod slides valve hydraulic fluid to enter the the chamber to a position that allows high-pressure behind the piston. This applies force hydraulic fluid to enter the chamber to the master-cylinderpushrod. behind the pressure piston. This Reserve is applies stored force in a to the master-cylinder ,pushrod. cylinder called an accumulator. There pressure stored in a is Reserve a very heavy spring is inside the accuThere cylinder called an accurn~~lato~: is a very heavy spring inside the accu-

Return Port Return Port

Power Section Power Section

Linkage Bracket

Bendix Hydro- Boost hydraulic brake booster mounts between master cylinder and brake pedal. High-pressure hydraulic fluid allows to be much smaller brake than vacuum Bendix unit Hydro-Boost hydraulic boosterbooster. mounts Hydraulic between pressure is supplied power-steering pump. Drawing courtesy master cylinder and by brake pedal. High-pressure hydraulic fluid Bendix unit Corporation. allows to be much smaller than vacuum booster. Hydraulic pressure is supplied by power-steering pump. Drawing courtesy Bendix Corporation.

Accumulator f ,-----\ I Power-Steering Gear f Accumulator

Spool Spool

t

t

Master Hydro-Boost Cylinder

Power-Steering D Pump C

Return Lines High-Pressure Lines

-

With Bendix Hydro-Boost power section in Pump ~7 High-Pressure Lines released position, most fluid from pump is. routed through power section powerWith Bendix Hydro-Boost powerto section in steering gear. Some fluid returns pump released position, most fluid from to pump is. reservoir throughpower return section port. Spring accurouted through to powermulator sufficient under pressteering stores gear. Some fluid fluid returns to pump sure to through provide return two port. or three reservoir Springpoweraccuassisted stores brake sufficient applications case presfluid mulator fluidinunder flow from power-steering sure t o provide two or pump three ceases. powerAccumulator is applications charged within fluid assisted brake case when fluid steering is turned or brakes are flow fromwheel power-steering pump ceases. applied. Drawing courtesy Accumulator is charged with fluidBendix when Corporation. steering wheel is turned or brakes are applied. Drawing mulator that appliescourtesy a force Bendix to a Corporation.

piston. Hydraulic fluid contained be-

mulator applies a force tween thethat piston and the end oftothea piston. Hydraulic fluid by contained becylinder is pressurized the spring. tween pistonis and of the If the the engine shutthe off,end pressure cylinder pressurized bypump the ceases. spring. from the is power-steering If the engine is shut off, pressure The pressurized fluid stored in the acfrom the power-steering pump ceases. cumulator is enough to apply the The pressurized fluid stored in the acbrakes several times with the engine cumulator is enough to apply the shut off. This safety feature allows the brakes times the stalls engine car to beseveral stopped if thewith engine or shut off. safety allows the car is This rolling with feature the engine off.the car to be stopped if the engine stalls or the car is rolling with the engine off. ADJUSTABLE PUSHRODS Most boosters are designed with adADJUSTABLE PUSHRODS justable master-cylinder push rods. Most are touch designed adThis rodboosters should just the with masterjustable master-cylinder pushrods. cylinder piston with the brakes

This rod should just touch the mastercylinder piston with the brakes

Hydro- Boost in released position (above) and applied position (below): With brake pedal depressed, input position rod and (above) piston Hydro-Boost in released moveapplied forward slightly. LeverWith assembly and position (below): brake moves sleeve forward, four pedal depressed, input clOSing rod andoffpiston holes center of spool. Formove leading forwardto open slightly. Lever assembly ward of spool closing allows additional movesmovement sleeve forward, off four hydraulic fluidt to entercenter cavity of behind holes leading o open spool.boosForter piston to pressurize This moves ward movement of spool area. allows additional piston and rod forward hydraulic fluidoutput t o enter cavity behindagainst boosmaster-cylinder pistons area. to apply ter piston to pressurize This brakes. moves Drawingand courtesy Bendix piston output rod Corporation. forward against master-cylinder pistons to apply brakes. Drawing Spool courtesy Moved Bendix Corporation. Forward Spool Moved

Piston , Pushrod and End Moved Forward Piston, Pushrod and End long rod will leave Moved Forward

released. A the master-cylinder compensating port released.and A cause long rod leave the covered brakewill drag. A short master-cylinder compensating port rod will add slop or excess pedal travel covered and cause brake A short to the system. See yourdrag. car's shop rod will add or excesson pedal travel manual for slop instructions adjusting to system. Seepushrod. your car's shop the the master-cylinder

manual for instructions on adjusting the master-cylinder pushrod. 81

Other Types of Brakes

8

Outlawed by most racing organizations, movable air brakes, such as one at rear of this 1955 300SLR Mercedes, are extremely effective at over 100 mph. Frontal area and drag coefficient are increased dramatically when air brake is activated. Photo courtesy Mercedes-Benz .

Outlawed by most racing organizations, movable air brakes, such as one at rear of this 1955 300SLR Mercedes, are extremely effective at over 1 0 0 mph. Frontal area and drag coefficient are increased dramatically when air brake is activated. Photo courtesy Mercedes-Benz.

In this chapter, I briefly describe brakes other than the traditional In this chapter, I briefly describe drum or disc brakes. Also, there are brakes other than the traditional several differeht ways to operate drum disc there brakes.areAlso, brakes.orAnd, otherthere waysare of several ways than to operate stopping different a vehicle other friction brakes. thereAlthough are other ways of at the And, tires. briefly stopping a vehicle other than friction discussed, I don't go into details on at the Although briefly other braketires. systems. The subject is discussed, I don't go into details on too extensive for this book.

FF = Force on Front Tires FA = Force on Rear Tires FF = Force on Front Tires We = Car Weight FR= Force on Rear Tires FD = Aerodynam ic Drag Wc = Car Weight RD = Rolling Drag FD= Aerodynamic Drag FT = Forward Thrust RD= Rolling Drag FA = Aerodynamic Downforce FT = Forward Thrust

FA = Aerodynamic Downforce

other brake systems. The subject is too extensive for thisDRAG book. AERODYNAMIC

& FA

v-

Drag acts to slow a moving car.

AERODYNAMIC DRAG Drag forces act toward the rear of the Drag acts to slow moving car. car when it is moving aforward . Drag

0 FR

FT

Forces on moving car: Vertical forces on the tires, FF and F R, are determined by car's weight and aerodynamic forces. Aerodynamic-drag force, F o' acts on car near center of body cross section,car: viewed from forces the front. Downforce, any,F actdetermined anywhere on Forces on moving Vertical on the tires, FFifand ,, canare by body. car's With thisand car,aerodynamic downforce isforces. mostly Aerodynamic-drag on rear wing. weight force, F, acts on car near center of

body cross section, viewed from the front. Downforce, if any, can act anywhere on body, With this car, downforce is mostly on rear wing.

82

Drag forces act toward theaerodynamrear of the consists of rolling drag and car when it is moving forward. Drag ic drag. Rolling drag is caused by resisrolling drag and aerodynarnconsists of tance of the tires to rolling, friction in ic drag. Rolling drag is caused the wheel bearings, and allby resisother tance of the tires to rolling, drive-train friction forces. friction in theRolling wheel drag bearings, and allexists other or resistance, at drive-train friction forces. all speeds, but increases with speed. Rolling drag or resistance, at You can experience rolling exists drag by all speeds, but on increases pushing a car a level with road.speed. You You drag will by must can keepexperience pushing or rolling rolling drag pushing a car on a level road. You stop the car. The force you use to drag must pushing O r stop the car. The force you use to

maintain speed equals rolling drag. Aerodynamic drag is caused by air maintain around speed equals rolling drag.The flowing the car body. Aerodynamic drag is caused by air force on the car is zero when air speed flowing around the car body. is zero. It increases with the squareThe of forceaironspeed. the carThis is zero whenthat air speed the means aerois zero. It increases with the square of dynamic drag quadruples if you the air speed. This means that aerodouble car speed. If a car has 100 lb of dynamic drag will aerodynamic dragquadruples at 30 mph ,if it you double carlbspeed. a carIfhas 100islbinof have 400 at 60 If mph. speed aerodynamic drag at 30 mph, it will creased to 90 mph, aerodynamic drag have 400 Ib atto 60900 mph. If speed inis increased Ib-9 timesis the creased to 90 mph, aerodynamic drag aerodynamic at 30 mph. drag At is increased 900 lb-9 force times onthea racing speeds,toaerodynamic aerodynamic dragtheatcar's 30 weight. mph. On At car can approach racing speeds, aerodynamic force on the very powerful land-speed-recorda car can the car's weight. On cars runapproach at the Bonneville Salt Flats, the very powerful land-speed-record aerodynamic drag gets so high the cars run theatBonneville Flats, to tires can at spin high speedSalt trying aerodynamic drag gets so high the overcome it! tires can spin atdrag highisspeed trying by to Aerodynamic determined overcome it! maximum cross-section size and the Aerodynamic dragThe is determined by of the car. cross-section shape maximum cross-section size and the size is called /rontal area. Frontal area shape of the car, cross-section is approximately theThe height of the car size is called frontal area. Frontal area is nearly times its width . Frontal area is a ~ ~ r o x i m a t e l the v height of the the same for most road cars, as it is car for most race cars in a given class. Shape the same for most cars,one as itcar is foi var ies a great dealroad from to most race cars in a given class. Shape another. Reducing drag by improving varies great streamlining. deal from one car to A streamshape isa called another. Reducing by improving aerodynamic drag lined shape has lowdrag shape is called streamlining. A streamfor its size. lined aerodynsmic Theshape shapehas of low the car compared drag to a for its size. standard flat shape is described by a The shape the drag car compared a coefficient.to A number calledof the standard shape is means described by a high dragflat coefficient a highnumber calledA the A lowdrag dragcoefficient. coefficient drag shape. high drag coefficient means a highmeans a streamlined shape. The worst drag shape.have A low drag coefficient of car shapes a drag coefficient means a streamlined shape. The worst nearly 1.0. The most streamlined cars car a drag coefficient of haveshapes a draghave coefficient of about 0.2. nearly 1 .O. The most streamlined cars Aerodynamic drag on a car varies have a drag of about 0.2. directly with coefficient its drag coefficient. For Aerodynamic drag on a car varies example, a car with a drag coefficient directly with its the dragaerodynamic coefficient. drag For of 0.6 has twice example, car with a drag coefficient as the same-size car at a givena speed of 0.6a drag has twice the aerodynamic drag of 0.3. with coefficient at When a giventhespeed the his same-size driveraslifts foot off car the with a drag coefficient of 0.3. throttle at high speed, drag on the car When the driver foot off the will rapidly slow lifts it. hisDeceleration throttle at high speed, drag on the car by equals the total drag force divided will rapidly slow it. Deceleration car weight. Above 60 mph, most drag equals the total drag force divided is aerodynamic. If a 2000-lb car hasbya car Above drag 500 lb60, itmph, will most decelerate dragweight. force of is aerodynamic. If a 2000-lb car has a at 0.25 g when not under power. Bedrag force of 500 Ib, it will decelerate cause aerodynamic drag drops as at 0.25drops, g when not under drops power.asBespeed deceleration car

cause aerodynamic drag drops as speed drops, deceleration drops as car

Except for lights atop body, custom Camaro pace car has improved streamlining on an already excellent body shape. Note smooth-flowing lines with a minimum of projections or corners. Except for lights atop body, Custom Camar0 pace car has improved streamlining on an al-

ready excellent body shape. Note smooth-flowing lines with a minimum of projections or corners.

Old sports cars are unstreamlined. Body shapes are rough, angular and have lots of parts sticking into airflow. Streamlining of cars refers to shape, not size of body. An unstreamlinedsports car has a higher drag force on itBody than shapes a streamlined car ofangular the same . lots of parts Old cars are unstreamlined. are rough, andsize have

sticking into airflow. Streamlining of cars refers to shape, not size of body. An unstreamlined has a higher drag force on drag it than is a streamlined car of of theobject same size. W = Weight in pounds speedcar drops. Aerodynamic

very low at low speeds.

speed drops.is Aerodynamic is the formula fordrag the acFollowing very low at low speeds. celeration of an object in g's. RememFollowing is the formulais fornegative the acber that deceleration celeration of an object in g's. Rememacceleration. ber that deceleration is negative Acceleration = ｾ＠ acceleration. F force on object in F = Unbalanced Acceleration = pounds F = Unbalanced force on object in pounds

w

that ifin the unbalanced W Remember = Weight of object pounds force acts in a direction to slow the Remember thathasif athe unbalanced object, that force negative value. force acts inforce a direction to slow the A negative makes the acceleraobject, thatobject force negative. has a negative value. tion of the A If negative force makes to the be a acceleraspeeding an object happens tion of the object negative. car and the driver lifts off the throttle, object hamens a speedinn force. theIf an unbalanced forcetoisbedrag

car and t h k drive; lifts off the throttle, the unbalanced force is drag force.

83

HOW TO CALCULATE AERODYNAMIC-DRAG FORCE HOWformula TO CALCULATE The for aerodynamic-drag AERODYNAMIC-DRAG FORCE force is simple:

on the paper is scaled at 1 inch on a side,the frontal area will come out on the paper is scaled at 1divide inch on a inches. If you the in square side, theoffrontal area will come out number square inches by 144, in square inches. you get square feet.If you divide the square number has inches nothingbyto144, do Frontalofarea you get with thesquare shapefeet. of the front ofa car. Frontal area has cross-sectional nothing to do Only the maximum front of Shape a car. with thethe shape size of car of is the important. Only the cross-sectional affects themaximum drag coefficient, not the size of the is important. Shape frontal area.carTypical drag coeffiaffects theproduction drag coefficient, notfrom the cients for cars vary frontal Typical coeffia low of area. 0.30 to a high drag of 0.60. The ' cientscoefficients for production cars vary for many carsfrom are drag a low in of magazine 0.30 to a articles high of 0.60. The and road given drag for article many cars are tests.coefficients Find such an for your given in magazine and road car to determine its articles drag coefficient. tests. Find such an article for your car to determine its drag coefficient.

The formula for aerodynamic-drag Aerodynamic drag force is simple: = 0.00256AFCoS2 in pounds Aerodynamic AF = Frontal drag area of car in square = 0.00256A,CDS2 in pounds feet Frontal area Of ofcar in 'quare CD == Drag coefficient body shape feet S == car speed in miles per hour D ' TheDrag 'OeffiCient Of body frontal area is the shape crossS = car speed in miles per hour sect·ional area of a car as viewed frontfrom front. area If you isdraw Thethefrontal the a crosssectional area of a viewed outline of the carcar on as a sheet of view from the front. You draw a frontandIf count the squares graph paper view of that the Car a sheet of will on approximate insideoutline outline, graph Raper andarea. COunt the squares the car's frontal H each square inside outline, that will approximate the car's frontal area. If each square

-

1500 Cd = Drag Coefficient

1500

Frontal Area = 25.4 sq It Cd = Drag Coefficient Frontal Area = 25.4 sq f t

Cd = 0.6

1000 Air Drag

1000 -

,/ /'

(Ib) Air

Drag (I b)

/ 500

500

ｯｌＭｾＫ

/" - C d =0.3

./

-

/

40

- --

/

80

0

40

/

80

120 Car

SpeedI

(mph)

120

160

200

I

I

160

200

I

Graph shows how aerodynamic drag varies with car speed and drag coefficient. Solid line is Car Speed (rnph) for unstreamlined car with a 0 .6 drag coefficient. Dotted curve is for streamlined car with the same frontal but half the drag, or 0.3 coefficient. Drag figures areSolid typical Graph shows howarea, aerodynamic drag varies withdrag car speed and drag coefficient. linefor is a large sedan. for unstreamlined car with a 0.6 drag coefficient. Dotted curve is for streamlined car with

the same frontal area, but half the drag, or 0.3 drag coefficient. Drag figures are typical for a large sedan.

The formu la for dece leration can be written another way:

The formula for deceleration can be . written another way: FD Deceleration of a car = WFDc Fa = Drag force of aoncarcar=in -- pounds Deceleration W,LJpounds Wc = Weight of the car in F, = Drag force on car in pounds W, = Weight of the car in pounds In this formul a, deceleration is In g's. If you know the drag forc e on a thiscan formula, deceleration is In. calculate its deceleration car,Inyou g's. If you know dragway, forceif on Approaching it anthe o ther youa car, you can calculate its deceleration. could measure deceleration , you Approaching another you could calculateitdrag force .way, This if is how could measure you vehicle drag can bedeceleration, determined withcould calculate force. This is how out using a winddrag tunnel.

vehicle drag can be determined without using a wind tunnel. AERODYNAMIC BRAKING If a car is streamlined and suddenly

AERODYNAMIC BRAKING If a car is streamlined and suddenly 84

increases its drag coefficient for braking while at high speed, it can slow increases This its dragis coefficient for brakquicker. how aerodynamic ing whileworks. at high speed, slow braking Added dragit iscan created quicker. This is how aerodynamic by changing the shape or size of the braking Added dragchange is created car. Theworks. drag-coefficient has by changing or size of the to be large tothe getshape a significant effect car. drag-coefficient fromThe aerodynamic braking.change Also, has the to be must large be to high. get a Itsignificant speed also helps effect if the from aerodynamic braking. Also, the car is light because deceleration speed mustonbe weight. high. It also helps aeroif the depends Finally, car is light because deceleration dynamic braking is worthwhile only depends weight. Finally, on a race on car that brakes at very aerohigh dynamic braking is worthwhile only speed . onAerodynamic a race car thatbraking brakes atis very high efficient speed. because there is no heat to dissipate in braking is efficient theAerodynamic brake system. Instead, aerono heat dissipate in because there dynamic drag isheats thetosurrounding the asbrake Instead, it. aeroair the carsystem. passes through The

dynamic drag heats the surrounding air as the car passes through it. The

wheel brakes can be applied along with aerodynamic braking for even wheel can be applied along higher brakes deceleration. Deceleration with aerodynamic brakingoperating for even with both brake systems is higher than deceleration. greater either systemDeceleration can achieve with both brake systems operating is Singularly! greater than either system can achieve If aerodynamic braking is so singularly!why is it used infrequently efficient, braking is so or If onlyaerodynamic on a few specialized race cars? efficient, why is it used infrequently • The braking force is useful only at or only onspeeds-near a few specialized very high 200 race mph.cars? braking force is useful at • The Aerodynamic braking will notonly bring very high speeds-near 200 mph. a car to a dead stop. The braking force Aerodynamic not nears bring approaches zerobraking as ca r will speed a car. to a dead stop. The braking force zero approaches zero brakes as car add speedweight, nears • Aerodynamic zero. complexity and cost. Aerodynamic brakesareaadd weight, • Because car frontal should incomplexity and cost. crease for aerodynamic braking to be Because the car frontal should ineffective, car willarea occupy more crease for aerodynamic braking to be space on the road with the brakes effective,This themay car mwill more applied. a ke occupy it difficult to space near on other the road drive cars. with the brakes applied. Thisracing may make it difficult to • In most classes, movable drive near other cars. aerodynamic devices are illegal. In most racingbrakes classes,have movable Aerodynamic been aerodynamic illegal. tried in roaddevices racing,are such as on the Aerodynamic brakes have Mercedes sports cars of the mid-been ' 50s tried in road racing, such as on the and early winged Can-Am Chaparral Mercedes sports cars of the mid-'50s racers. and early winged Chaparral Mercedes used aCan-Am flap-mounted flat racers. on the tail of their 300SLR. This fl ap Mercedes used a flap-mounted flata was raised hydraulically by operating on the tail of their 300SLR. flap control valve in the cockpitThis , nearly was raisedthe hydraulically doubling frontal areabyofoperating the car. Ita control valve in the cockpit, nearly also made the airflow more turbulent. doubling the frontal area of the car.tal It The combination of the larger fron also made the airflow more and air turbulence more thanturbulent. doubled The combination the larger frontal aerodynamic drag .of Because this car exand air turbulence more than doubled ceeded 180 mph on the 3-mile aerodynamic drag. Becauseand this car straightaway at LeMans, had exto ceeded mph hairpin on theturn, 3-mile slow for 180 a 30-mph the straightaway LeMans, hadload to aerodynamic at brake took a and lot of slow for a 30-mph hairpin turn, the off the wheel brakes. Competing drivaerodynamic brake a lot ofprobload ers complained abouttook a visibility off wheel Competing drivlemthe when thebrakes. Mercedes aerodynamic ers complained about a visibility brake was raised. This, however,probwas lem when the Mercedes aerodynamic probably due to the superiority of the brake was raised. was Mercedes rather This, than ahowever, "visibility" probably hazard. due to the superiority of the Mercedes rather ran than a "visibility" The Chaparral a large wing over hazard. the rear wheels, which could be The Chaparral large wing over of aattack. The wing varied in its angleran the rear wheels, which could be ran at low angles when the car was varied in its angle of attack. The wing accelerating, to give some downforce ran at anglesdrag when the car and to low minimize created by was the accelerating, to give some downforce wing. When braking, the driver could and to minimize drag created by the tip the wing to maximize downforce wing. When braking, the driver could and drag . The downforce increase on tip to maximize downforce the the rear wing tires allowed more rear-wheel and drag.Because The downforce on braking. this car increase was highly the rear tires allowed more rear-wheel successful, the racing rules were braking. Because car was highly changed, banningthismovable aerosuccessful, the racing rules were dynamic devices.

changed, banning dynamic devices.

movable

aero-

High-Drag Position

High-Drag Position

Aerodynamic brake on the Chaparral Can-Am car was similar to this. Wing in low-drag position supplied downforce to rear tires for improved high-speed cornering. When flipped to high-drag Aerodynamic brake on the Chaparral Can-Am car was similar to position, aerodynamic increased deceleration . Movathis. Wingadded in low-drag positiondrag supplied downforce to rear tires for ble wings are illegal in road racing today. improved high-speed cornering. When flipped to high-drag

Aerodynamic braking has been used for years in drag racing. Racing chutes stop funny cars much quicker than ordinary brakes. Cars are traveling near has 250 been mph atused finishfor line. After in each run,racing. paraAerodynamic braking years drag chute ischutes repacked. would work for cars brakes are Racing stopThis funny cars not much quicker thanwhere ordinary brakes. applied than once during a race. mph at finish line. After each run, paraCars aremore traveling near 250

position, added aerodynamic drag increased deceleration. MovableAerodynamic wings are illegalbraking in road racing has today. found a

chute is repacked. This would not work for cars where brakes are applied more than once during a race.

home in drag racing. All the really fast Aerodynamic braking has found drag cars, such as top fuelers , funnya homeand in drag racing. All really fast cars pro stockers, usethe a parachu te drag cars, such asBecause top fuelers, funny to assist stopping. a parachute cars pro stockers, use a parachute reliesandon aerodynamic drag for to assist stopping. Because a parachute effectiveness, it is true aerodynamic relies aerodynamic dragwon't for braking. on Obviously, a parachute effectiveness, it is ortrue aerodynamic work in road racing on the street bebraking. Obviously, a parachute cause it has to be repacked afterwon't each work in road racing or on the streetis beapplication. In a drag race, this no cause it has to be repacked after each problem because the car makes one application. a drag this is no stop per run.InThe chuterace, is repacked by problem because the car makes the pit crew prior to the next run . one stop per drag run. The is repacked by Some cars chute reach or exceed 250 the pitand crew the next run. , the mph areprior veryto light. If large Someapplies drag cars reachmore or exceed 250 chute much stopping mph and are very light. If large, force than the wheel brakes, thusthe is chute applies muchin more stopping extremely effective reducing speed force than100themph wheel thus is to under in a brakes, short distance. extremely In fact, theeffective only limitintoreducing how fastspeed a car to under mphwith in a ashort distance. could be 100 slowed chute is the In fact,force the only to how fastwitha car inertia that limit the driver must could when be slowed withopens. a chute is the stand the chute inertia force that The critical partthe of driver settingmust up a withdragstand opens. racingwhen chutetheischute where and how the Themounts critical part of setting a dragchute to the frame. up If mountracing chute is where and the howchute the ed off-center, when opened chute mounts to the frame. If mountwill cause the car to swerve. Ideally, ed when opened the off-center, mount should be near the thechute CG will cause car to swerve. Ideally, height, andthe centered. The maximum the mount should bemount near is themany CG force on a parachute height, and centered. The maximum tons, so mount strength is critical. force on a mounts parachutehave mount is many Parachute ripped off tons, leav so ing mount strength cars, the driver only isthecritical. wheel Parachute haveThe ripped off brakes to mounts stop with. mount cars, leaving the driver theseveral wheel should be strong enoughonly to lift brakes stop with. who Thesellmount race cars to from it. Those dragshould be strong enough to several race parachutes, such as liftSimpson race cars from it. Those who sell dragSafety Equipment Co., can provide inrace parachutes, such and as setting Simpson structions on mounting up Safety Equipment Co., can provide inthe system.

structions on mounting and setting up the system.

Compressed air moves brake shoes by means of an actuating chamber mounted on axle housing. chamber rotates Compressed airActuating moves brake shoes by tube (arrow) pushrod and mounted lever to means of an through actuating chamber move brake shoes against chamber drum. Note lack on axle housing. Actuating rotates of backing plate on these truck and brakes. tube (arrow) through pushrod lever to

move brake shoes against drum. Note lack of backing plate on these truck brakes.

PNEUMATIC BRAKES Pneumatic brakes, commonly called PNEUMATIC BRAKES air brakes, refer to the actuating Pneumatic brakes, commonly system. Pneumatic brakes use called comair brakes, to the the brakes actuating pressed air torefer operate insystem. Pneumatic This brakes comstead of hydraulics. typeuse of brake pressed isair to primarily operate the brakes insystem used for large comstead of hydraulics. This type of brake mercial vehicles. A truck usually uses system is used primarily for large pneumatic brakes because therecomare mercial vehicles. usuallybrake uses advantages over Aa truck hydraulic pneumatic brakes because there are system. advantages a hydraulic brake Pneumaticover brakes are actuated by system. compressed air supplied by an enginePneumatic brakes areThe actuated by driven air compressor. comprescompressed air supplied by an enginesor supplies high-pressure air to a stordriven compressor. The compresage tankair , which is big enough to mainsor supplies high-pressure to a stortain pressure when the air brakes are age tank, which is big enough to mainapplied. tain pressure air when theto brakes are Compressed is fed the brakeapplied. system by valves controlled actuating is fedIfto the the brakeby Compressed the brake air pedal. driver actuating system by valves controlled by the brake pedal. If the driver

Pneumatic truck brakes are actuated by compressed air supplied by engine-driven air compressor. reservoir emergenPneumatic truckAirbrakes arehas actuated by cy supply of air brakes by won't fail if comcompressed air so supplied engine-driven pressor belts break. air compressor. Air reservoir has emergen-

cy supply of air so brakes won't fail if compressor belts break.

pushes harder on the brake pedal, more air pressure is applied to the pushes on the brake pedal, brakes. harder The driver is not supplying more air pressure is applied to the force or air movement, so the his brakes. The driver is not supplying strength doesn't matter. theBecause force ortrucks air movement, his are very so heavy strength doesn't matter. under full load, power-assisted hyBecause trucks very heavy draulic brakes wouldare be necessary. A under full load, ofpower-assisted hymajor advantage pneumatic brakes draulic necessary. A is they brakes have would built-inbe power assist. major advantage of pneumatic brakes Another advantage is pneumatic is theyarehave built-in by power brakes not affected smallassist. leaks Another advantage is pneumatic in the system. Air is supplied continubrakes by arethe not compressor, affected by small leaks ously so unless in the system. Air is supplied continuthere is a huge hole in the system, ously by the compressor, unless there is never a loss of so pressure. there is athe hugeairhole in the system, Instead, compressor must there harder is never a loss ofpressure pressure. work to maintain in Instead, the storagethe tank.air compressor must work to maintain pressure in The harder pneumatic system does not use the storage tank. hydraulic fluid, so it is not affected by

The pneumatic system does not use hydraulic fluid, so it is not affected by 85

Aircraft multi-disc brake: Brake, which is buried in wheel, is good for one stop after landing. Brake must cool Brake, before which another Aircraft multi-disc brake: is landing in can be made. buried wheel, is good for one stop after landing. Brake must cool before another landing can be made.

the reduced boiling point of old, contaminated fluid. Thus, the system can the much reducedlonger boilingbetween point of servicing. old, congo taminated fluid. Thus, the system can This is important on long-haul trucks. goThe much longer between servicing. disadvantages of a pneumatic This important n long-haul trucks. brakeissystem are osize, complexity and T h eAlso, disadvantages of a pneumatic cost. it takes engine power to brakethe system are size, complexity and run air compressor. System prescost. Also, it takes engine power to sure is much lower than that of a hyrun the system. air compressor. System presThus, the diameters draulic sureallis much than that of a and hyof the lower cylinders-master draulic system. T h u s , the diameters wheel- are much larger. Trucks have of the cylinders-master and lots all of room, so there's no problem wheel-are larger. Trucks havea fitting large much cylinders. But size has lots of room, so there's no problem definite disadvantage: It takes time to fitting large cylinders. But size has a build up pressure at the brakes. definite It takes timethe to There disadvantage: is a small delay between build the up pressure at the time driver hits thebrakes. pedal and the Thereactually is a small delayEngineers between can the brakes apply. time the driver hits the pedal and the design a system to reduce, but not brakes actually apply. Engineers can eliminate, this time lag. design a system reduce, but not Compressor costtomakes a pneumateliminate, this time lag.expensive than ic brake system more Compressor cost makes a pneumata hydraulic system. However, because ic brakecommercial system morevehicles expensive than many require a hydraulic system. However, because compressed air to run other systems many vehicles on the commercial vehicle, the cost of therequire comcompressed air to run other systems pressor is justified, considering its o n the vehicle, the cost of the comdouble-duty function. pressor consideringin itsa There isarejustified, other complexities double-duty function. pneumatic brake system. The comThere must are other in a pressor have complexities a pressure-relief pneumatic brake over system. T h e comvalve to prevent pressurizing the pressor must a pressure-relief system. Also, have there's a pressurevalve to prevent overpressurizing controlled unloader that takes the the system. Also, there's a pressureload off the compressor once storagecontrol led unloader the reaches that abouttakes 100 psi. tank pressure load off the compressor once storageThere are also one-way valves to tank pressure reaches pressure about 100if psi. maintain storage-tank the There are also one-way valves to compressor fails. maintain storage-tank introduce pressure ifboth the Air compressors compressor fails. water and oil into a brake system.

Air compressors introduce both water and oil into a brake system.

86

HPBooks' very "slippery" Monza at Bonneville Salt Flats. To illustrate effect aerodynamic drag has on speed, Tom Monroe set C/Production record in car at 217.849 mph. Power was by fuel-injected 370-cubic inch small-block Chevy. Salt AlProduction record iseffect 219.334 mph, set in drag a '67 HPBooks' very "slippery" Monza at Bonneville Flats. To illustrate aerodynamic Camaro powered by Monroe a 510-cubic inch big-block-Chevy-37% displacement andwas 0.68% has on speed, Tom set ClProduction record in car atmore 217.849 mph. Power by faster! This is a good-news/bad-news when it comes to is braking. two set cars fuel-injected 370-cubic inch small-block situation Chevy. NProduction record 219.334 Ifmph, in awith '67 different drag coefficients are traveling at the same speed and more stop at the same deceleration Camaro powered by a 510-cubic inch big-block-Chevy-37% displacement and 0.68% rate, carThis withisthe lower Cd will require the higherwhen braking force. Photo by BillIf Fisher. faster! a good-newslbad-news situation it comes to braking. two cars with different drag coefficients are traveling at the same speed and stop at the same deceleration rate, car with the lower C, will require the higher braking force. Photo by Bill Fisher.

These liquids are removed to prevent the pneumatic system from being These liquids removed prevent damaged. Not are only can the toparts corthe systembutfrom rode pneumatic due to moisture, they being could damaged. only brake can the parts corfreeze andNot cause failure. The rode d u e to moisture, they could fluid-removal system but is similar to freezetraps and in cause brake failure. T h e compressed-air fluid a shop fluid-removal system is similar to system. fluid traps in brakes a shoparecompressed-air Pneumatic actuated by a system. diaphragm inside a housing, rather Pneumatic actuatedThese by a than a pistonbrakes in a are cylinder. diaphragm inside a housing, rather units are the brake chambers. You can thanthem a piston in aoncylinder. see mounted the rearThese axles units are trucks the brake You can of large and chambers. trailers. They are see n the rear too them big to mounted fit insideo wheels, so axles they of large the trucks andthrough trailers.a They are operate brakes shaft and too big to fit inside wheels, so they mechanical linkage. A return spring operatethe t h e chamber brakes through a shaft and inside returns the diamechanical A position return spring phragm to itslinkage. retracted when inside the are chamber returns the diathe brakes released. phragm to its retracted position when On some large off-road commercial the brakes are as released. vehicles such earth movers, graders O n road s o m e large off-road commercial and rollers, a combination vehicles such as earth movers, hydraulic/pneumatic system isgraders used. and road to rollers, a combination Referred as an air-aver-hydraulic hydraulic/pneumatic is used. system, the brakes aresystem operated by a Referred to as an air-over-hydraulic hydraulic system, but the hydraulic system, the brakes are by a system is applied by operated a pneumatic hydraulicbetween system,thebutbrake the pedal hydraulic system and system is applied a ispneumatic the hydraulic system.byThis a type of system assist between brake and power thattheuses air pedal pressure the hydraulic system. This is a type of rather than vacuum.

power assist that uses air pressure rather than vacuum. MULTIDISC BRAKES A multi disc brake works like a mul-

MULTIDISC BRAKES A multidisc brake works like a mul-

tidisc clutch. There are a number of driven and statianalY discs in a stack. tidisc clutch. There are a number of Friction material is between the discs. drivendriven and stationary discs inwith a stack. The discs rotate the FrictionWhen material between discs. wheel. theisbrakes arethe applied, T h e driven discs rotate with the the stack is clamped together. The stawheel. h e n thebecause brakes are tionary Wdiscs, theyapplied, can't the stack is clamped together.discs T h e starota te, slow the rotating by tionary discs, because they can't friction. rotate, slowbrakes the rotating by Multidisc are small discs and light friction. compared to other types of brakes Multidisc small and light that absorbbrakes the are same energy. compared to other types of brakes However, because the rubbing surthat are absorb the same energy. faces all "buried" inside the unit, However, becausecool theslowly. rubbing sur-a multidisc brakes Thus, faces are all "buried" inside the unit, multidisc brake is good for only one multidisc cool slowly. Thus, hard stop. brakes Considerable cooling timea multidisc is good for only is needed brake before the next stopone is hard made.stop. Considerable cooling time is The needed before theof next stop is compactness a multidisc made. brake makes it desirable for aircraft T h An e compactness of a wheels multidisc use. airplane has small to brakespace, makesmaking it desirable aircraft save a tight for fit for any use. hasstops small wheels to plane only hard once as brake.A nA airplane save space, making a tight fit for any it lands, and has a great deal of cooling brake.before A plane only stops hardand once as time another landing stop. it lands, has a great of cooling And, theand extremely highdeal temperatures time beforein another landingdictate and stop. generated aircraft brakes the And, the extremely high temperatures use of sintered-metallic or graphitegenerated in aircraft brakes dictate the composite friction materials. useAircraft-type of sintered-metallic or graphitemultidisc brakes composite friction materials. might work well on dragsters or landAircraft-typecars, multidisc brakes speed-record but to my knowlmightthey workhave wellyet o ntodragsters edge be used or on landsuch speed-record cars, but to my knowlvehicles.

edge they have yet to be used o n such vehicles.

Dragster brake is operated by hand lever. Note pushrod between lever and master cylinder (arrow). Hand-lever movement can be more than a brake pedal, so higher pedal ratio is possible lever-operated Dragsterwith brake is operated bybrakes. hand lever. Note pushrod between lever and master cylinder

(arrow). Hand-lever movement can be more than a brake pedal, so higher pedal ratio is possible with lever-operated brakes.

HAND-OPERATED BRAKES Some specialized cars use a brake HAND-OPERATED system operated by BRAKES a hand lever Somethan specialized cars use a brake rather a brake pedal. A dragster system by dragster a hand handLever is one ofoperated these. The rather than a brake pedal. A dragster lever brake operates identically to a is one of these. dragster foot-pedal brake,Thebut with handtwo lever brake operates identically to a differences: foot-pedal but awith two • Maximum brake, force with person's differences: hand is less than can be applied with a Maximum force with a person's foot. hand is -lever less than can becan applied with a • Hand stroke be longer foot. than a foot pedal, allowing a higher Hand-lever stroke can be longer ratio . than pedal, allowing a higher Likea foot a foot-brake pedal, the hand ratio. operates a master cylinder lever Like aa foot-brake pedal, the hand through pushrod . Because dragsters lever operates a master cylinder have rear-wheel brakes only, a single through a pushrod. Because dragsters master cylinder is used. Most of the have rear-wheel only, a single stopping is donebrakes by the parachute. masterwheel cylinder is used. Most atof low the The brakes are used stopping is done by the parachute. speeds, particularly for holding the The brakesline. are used at low car onwheel the starting speeds, particularly holding the Another type offorhand-operated car on the starting line. brake is found on dune buggies. Another hand-operated Known as a type CUllingofbrake or steering brake found dunelevers buggies. brake, itis has one on or two with Known as a cutting brake or two separate master cylinders tosteering operit hasorone or two levers with brake, ate the right left rear wheel. two separate master cylinders to operCutting brakes are used for steering ate rightinorsoft left sand rear wheel. the the buggy or tight turns. Cutting brakes are do used steering The front tires often notfor have suffithe buggy in soft sand or tight cient bite for steering control in turns. these The front tires often do not tires have suffisituations. Because rear have cient steering these more bite bite,forthey can control turn thein buggy situations. Because rear is tires have quickly when one wheel braked. A

more bite, they can turn the buggy quickly when one wheel is braked. A

Ja-Mar cutting-brake assembly is used on sand buggies for steering control in soft sand. One operates one master cylinder Ja-Mar cutting-brake assembly is used on when buggies pulled; other lever operates sand for steering controlopposite in soft cylinder. Each master one cylinder is designed sand. One operates master cylinder to operate a single when pulled; other rear leverbrake. operates opposite

cylinder. Each master cylinder is designed t o operate a single rear brake.

Disc-brake caliper can be operated by either hydraulic pressure or separate mechanical linkage. Used on competition rally cars at the rear wheels and operated by a mechanical linkage by a caliper parking-brake driver pull hydraulic lever to slide out rear formechanical entering a Disc-brake can be lever, operated bycan either pressure or wheels separate turn. This allows ultra-tight turns to beatnegotiated quicklyand in operated dirt or onbyslick surfaces. linkage. Used on competition rally cars the rear wheels a mechanical Courtesy Racing. linkage byAP a parking-brake lever, driver can pull lever to slide out rear wheels for entering a

turn. This allows ultra-tight turns t o be negotiated quickly in dirt or on slick surfaces. conventional brake pedal is used for wheel drive. It is handy for the driver Courtesy AP Racing.

braking the

buggy during

normal

conventional brake pedal is used for operation . braking the buggy during normal Hand-operated rear-wheel brakes operation. also are found on competition rally Hand-operated rear-wheel cars. Unlike a cutting brake,brakes rearalso are found on competition rally wheel rally-car brakes are operated cars. Unlike a cutting rearsimultaneously with brake, one hand wheel rally-car brakesRally are operated lever/master cylinder. cars run simultaneously with hand on slick roads and often one have frontleverlmaster cylinder. Rally cars run on slick roads and often have front-

to brake only the rear wheels to throw

wheel handy for skid. the driver the cardrive. into Ita isdeliberate This to brake the rear wheels to throw helps to only negotiate tight slippery turns the car steering into a deliberate where control skid. might This be helps to negotiate tight slippery turns marginal. Separate from the hydraulic where steering control might be system, special mechanical linkages marginal. are often Separate used forfrom the the rearhydraulic brakes. system,is special linkages This similarmechanical to parking-brake are often used for the rear brakes. linkage, but is designed for severe use . This is similar to parking-brake linkage, but is designed for severe use. 87

High-Performance Brakes

High-Performance Brakes

9

Design of modern race-ear-brake system is not arrived at through magic. Instead, carefully planned steps are required. Success starts with a written statement of what brake system must do. This is your design criteria. Don't lose sight of it when you're deep into the design. Design of modern race-car-brake system is not arrived at through magic. Instead, carefully planned steps are required. Success starts with a written statement of what brake system must do. This is your design criteria. Don't lose sight of it when you're deep into the design.

If you are designing a special car for either street or racing use, you'll also If you are designing a special car for have to design the brake system . It's either racing use, you'llbrake also difficultstreet to or take a complete have to from designone thecarbrake It'sa system and system. use it on difficult to take a complete brake different one and have it work system car andconfiguration use it on a Carone weight, properly.from work different one andall have and performance affeciit brakeproperly. Car weight, configuration system design . and performance design all affecr brakeBy brake-system I mean putsystem design.a group of components ting together mean putBywork brake-system that properly. design I'll notI attempt to ting together a group of components discuss how to design a brake rotor or that work properly. not attempt to proportioning valve.I'll Instead, I will discusshow how to brakenecessary rotor or show to design make a the proportioning plan valve. I will the Instead, entire system, calculations, show how to make the necessary and select the components to do the calculations, plancomponents the entire system, job . The correct already and select the components to doprobthe exist, regardless of the car. The job. The correct components already lem is selecting the right ones for your exist, regardless of the car. The probcar. lem is selecting the right ones forbrakeyour This chapter covers complete car. system design . If you have an existing covers to complete brakeare trying improve the carThis andchapter system design. If you have an existing brakes, read Chapter 12. However, if car and are tryingthetocarimprove the you are designing rather than brakes, read Chapter 12. However, if modifying it, you have more choices.

you are designing the car rather than modifying it, you have more choices.

88

There are fewer ways you can easily change an existing car. This is why the There fewerbeways you canplanned easily design are should carefully change an existing car. This is why the before buying or building parts. design should be carefully Brake-system design requiresplanned severbefore buying or building al steps. There are many parts. ways to apBrake-system design requires proach the design process, butseverhere al steps. There are many ways to apare my suggestions: proach the design • List design criteria.process, but here are my suggestions: • Calculate forces on tires. List design brake criteria.torques at maxi• Calculate Calculate forces on tires. mum deceleration. braketype torques at maxi• Calculate Choose brake and mounting mum deceleration. location . Choose brake type and mounting • Determine hydraulic pressure relocation. quired. Determine hydraulic pressure pedal-and-linkage design.re• Choose quired. • Calculate master-cylinder diameter Choose pedal-and-linkage design. required. Design restmaster-cylinder of brake system.diameter • Calculate required. There may be some reason to rearDesign reststeps. of brake range these Forsystem. instance, you There mayhave be some reasonand to rearthe pedals wish may already range these steps. For instance, you to retain them. That'll work fine may already have the pedals and wish unless you have to compromise braketo retainperformance them. That'll system to do work it. But,fine if unless you have to compromise existing components won't givebrakegood

system performance to do it. But, if existing components won't give good

brake performance, don't use them. The brakes are too critical to comprobrake performance, use them. mise because of a few don't extra dollars.

The brakes are too critical to compromise because of a few extra dollars. DESIGN CRITERIA The first step in any design process

DESIGN is listing CRITERIA the reasons for the design

The step in any and thefirst objectives. Thisdesign writtenprocess docuis listing the reasons the design ment is your design for criteria. For a and objectives. Thissheets written brakethe system, several of docupaper ment is your design criteria. For a should be enough. You are writing brake system, several the criteria so you can sheets refer toofit paper later. should be enough. You are Keep your design-criteria list writing handy t later. the criteria you can referthe to idesign during and read itsooften Keep your design-criteria list process. Don't lose track of handy your and read it often during the design objectives. process. Don't lose criteria track ofshould your A brake-design objectives. answer the following questions: brake-design criteria will should Under what conditions the • A answer the following brake system have to questions: operate? Underlong what conditions the • How do you expect thewill system brake system have to operate? to last? How youfor expect thestreet system • Is car long to bedo used rac ing, or to last? both? car toperformance be used for racing, street or • Is What specifications both? the brakes meet? should What specifications • If you performance have to compromise on should the brakes meet? If you have to compromise on

Road will withstand withstand exRoad cars must have have brake brake components components that will treme cold. cold. Corvette master cylinder cylinder and and booster booster are being being tested at S8F 58F below below zero (-SOC). (-50C). Road-car brake brake manufacturers manufacturers must must test components components under extremely severe conditions. conditions. If designing designing a special special car, you can can save money by limiting limiting conditions conditions car has has to operate under. under. Photo Photo courtesy Girlock Girlock Ltd. Ltd.

)

, I)

specifications, what is most important? What is least important? • What are maximum loads imposed on system? system? What are normal operatloads? ing loads? Conditions-Think twice Operating Conditions-Think about this one: It is much harder to design a brake system to perform under every possible operating condicondiuse. For tion than it is to limit its use. instance, do you want the brake system to function in the rain? Will it get used in sand dunes like an off-road vehicle? Is it used strictly for drag racing, where there's a long cool-down racing, period after each stop? stop? Will the car be roads? used on icy, icy, salted roads? specific and practical about the Be specific conditions your vehicle will likely encounter. The more operating condiencounter. tions you can eliminate or minimize, the easier and cheaper the job will be. The most difficult job an engineer has to do is design a car that will be driven on the street, in races, off-road and in weather conditions ranging from the burning deserts to sub-zero cold. cold. With luck, your special car will have specialized operating conditions for specialized the brakes. brakes. This will eliminate some extremes. Life-Every car component Design Life-Every or system has a certain life assumed when the engineer designs it. it. Most road-car parts are expected to last at

Easiest Easiest car to design design is is one with a special special purpose-win purpose-win sportscar races, races, in in this case. If car also also had had to transport wife and and kids kids to church would church on on Sunday, Sunday, and and still still win races, races, race-car designer would really really have a tough tough job. Be Be realistic, realistic, but limit limit functions car must must perform-design will be easier. perform-design job will easier.

least 50,000 miles, but often last twice that. If every car were designed to last 40 years, the cars would be too expensive and much heavier. If something is designed for a long life, more. So life, it costs more. restrict long-life items to those that are safety-related. safety-related. Because brakes are safety-related, the structure of the brake system should be extremely durable. You choose the miles, time or number or races. If you are using passenger-car brake parts and will be operating them at less than their original design loads, you can expect them to last a long time. Some brake-system parts wear out quicker than the basic system. This includes the linings, seals and, rotors. sometimes, the drums and rotors. Parts that wear should be designed to don't manner-so they don't do so in a safe manner-so cause a loss of braking. Conventional brake systems are so designed. Therefore, if you use conventional design practice, the brakes will be safe when parts wear out. out. What life do you expect wear-prone brake parts to have? If the linings you 10,000 miles on a are using last 10,000 2500-lb sedan, you can expect them 1500-lb to last at least that long on a 1500-lb way. Use sports car driven the same way. life. comparisons to predict useful life. However, if you drive your special car

Always consider the application: application: If stockcar designer failed to consider consider that car might might compete compete in in road road races with right right turns, driver would be be in in trouble. It is is easier design a car for left turns only. only. Likewise, Likewise, to design it's easier to design design brakes brakes for a short track with high-banked high-banked turns than than one with long long straights and and flat turns.

harder than the sedan that weighs the same, don't expect the linings to last the same. More brake-lining area or a harder lining would be needed to compensate. You cannot make an exact predicprediction of brake life. life. However, write down what you are expecting and keep the desired life in mind while designing the brake system. system. You must have a design goal. goal. This decision Racing vs. Street UseUse-This must be made early in the design process. Make usage part of your criteria. The brake system that works 89

Production-sedan designers have the most difficult design job. I wonder if the VW brakedesign engineers visualized Rabbits racing at Riverside on a hot summer day? Brakes get a severe workout compared to their Production-sedan designers haveeveryday the most highway difficult service. design job. I wonder if the VW brake-

design engineers visualized Rabbits racing at Riverside on a hot summer day? Brakes get a severe workout compared to their everyday highway service.

SAMPLE PERFORMANCE SPECIFICATIONS Car SPECIFICATIONS A Car B SAMPLE PERFORMANCE Type of car Usage Type of car Percent racing use Usage Horsepower Percent racing use Car weight Ob) -average racing Horsepower distribution (front/rear) Weight Car weightcar (Ib)weight -average (Ib) racing Maximum Weight distribution Minimum car weight(fronthear) (Ib) Maximum speed car weight (Ib) Maximum (mph) Minimumrace car weight (Ib) Average speed (mph) Maximum race speedduration (mph) (minutes) Maximum Average race 0-60 speedmph (mph) Acceleration (seconds) Maximum tire racegrip-street duration (minutes) Maximum Acceleration mph (seconds) Maximum tire0-60 grip-racing Maximum tire grip-street Maximum deceleration-street (g's) Maximum tire grip-racing Maximum deceleration-racing (g's) Maximum deceleration-street (g's) Downforce at top speed (Ib)

Maximum deceleration-racing (g's) Downforce at top speed (Ib)

Sports Car Car A Street & slalom Sports Car 5% or less Street 200 8 slalom 5% or less 2000 200 50/50 2000 2400 (street) 50/50 2000 (racing) 2400 125 (street)

2000 (racing) 60

5125 860 5 0.9 8 1.2

0.9 0.9 1.2 1.2

Race car Car B Road racing Race 100% car Road 150 racing 100% 1100 150 40/60 1100 (max fuel) 1150 40/60 1050 (min fuel) 1 150 (max fuel) 150 1050 (min fuel) 100

150 60 6100 60 6 1.4

-

0.9 o

1.4 (with wings) 2.0 500

0

500

1.2

2.0 (with wings)

Performance specifications for two imaginary cars: Car A is a sports car designed for both street use and slaloms; car B is an all-out race car for a small formula-car class. Note how road-car's weight can vary. for Brake must be able to is accommodate all variations, but Performance specifications twosystem imaginary cars: Car A a sports car designed for both remain balanced. street use and slaloms; car B is an all-out race car for a small formula-car class. Note how

road-car's weight can vary. Brake system must be able to accommodate all variations, but remain balanced.

best for racing is not the best for the street and vice versa. Either system best bestwhile for the will for workracing OK isfornota the little in street and vice versa. either application, but Either you willsystem have will worksooner OK for a little while in problems or later. either application, but youracing, will have Remember that while the problems sooner or later. brakes are usually warmed up before a Remember the hard stop; theythat are while not onracing, the street. brakes are usually warmedrequire up before Street-driving conditions pro-a hard stop; on the street. tection fromthey dirtare andnot corrosion; racing Street-driving conditions require conditions may not. Some formsproof tection from dirt and corrosion; racing are much worse than racing street conditions Some formsand of driving for may bothnot. contamination racing are much worse than street high temperatures. driving for both contamination The hardest thing to design is a and car high istemperatures. that used for both street driving and

The hardest thing to design is a car that is used for both street driving and

90

racing . If you attempt this, you must make design compromises that will racing.theIf you this, you hurt car'sattempt performance in must both make design compromises situations. Therefore, try to that limit will the hurt' s operating the car's conditions, performance both car for in highest situations. Therefore, to limit the performance and lowesttry cost. car's operating conditions, highest Performance Specs - List for specificaperformance andtolowest tions you want meet. cost. Because each Performance -List specificatype of vehicleSpecs has different specs, I tions you want to meet. Because can't give you a list for your each car. type of vehicle has different specs, aI However, the above table gives can't youfora two list types for your car. samplegive listing of cars. However, the weight above and tablespeed givesarea Note that car sample for two ittypes cars. included.listing Obviously, takesof more Note that car weight and speed bra ke to stop a fast, heavy car thanare it included. takes more does to stopObviously, a light, slowitone.

brake to stop a fast, heavy car than it does to stop a light, slow one.

Maximum loads on car may occur during an off-road excursion or some other emergency situation. Normal loads don't Maximum loads on caroperating may occur during an include unexpected in other the rough stuff, off-road excursion ortrips some emergenbut such conditions be allowed in cy situation. Normalmust operating loads for don't a design,unexpected including driver include trips error. in the rough stuff,

but such conditions must be allowed for in

a design, including driverand error. Include car weight CO location

in the performance specifications. Include weight CG you location You must car know theseand before can in the performance specifications. design the brake system. When startYou know ,these youknow can ing amust car design you before may not design the weight brake system. When startthe exact or CO location. To ing a the car design, you may not , know start brake-system design estithe exact weightand or CO CG location location.forToa mate the weight start the brake-system design, esticar such as yours. Then you can begin mate brake-system the weight and C G location for a your design . carAfter such as can begin caryours. and Then brakeyou system are your brake-system design. designed, go back and do all the calcuAfter again car and brake lations using the system exact are car designed, go CO back location and do all calcuweight and . Ifthe you eslations using car timated again correctly the the first exact time , few weight and C Gchanges location. should If you esbrake-design be timated .correctly theit first time,takes few required However, usually brake-design changes shouldeffort be two or three rounds of design required. However, it usually takes before an entire car design is two or three completed . rounds of design effort

before an entire car design completed. BRAKE-SYSTEM LOADS

is

As already discussed , the two loads

BRAKE-SYSTEM LOADS to be concerned with are maximum As and already discussed, two Maxiloads loads normal operatingthe loads. to be concerned with are maximum mum loads on most brake compoloads and normal operating loads. Maxinents occur during an emergency. It mum loads on most brake where compo-a could be a panic situation nents occur during It crash may be aboutan toemergency. occur. The could be a panic situation where driver panics and slams his foot on thea crash may as be hard about to can, occur. The brake pedal as he usually driver panics and slams footresult on the locking the wheels. Thishis may in brakeofpedal as hard he can, loss control or as worse . It usually is the locking the wheels. This may result in maximum-loading condition for the loss of control or worse. It is the brake pedal and linkage. maximum-loading condition for the There may be different maximumbrake pedal and linkage. load conditions for parts of the brake There other may bethan different system the maximumpedal and load conditions for parts the brake linkage. A brake-reservoirofbracket exsystem than the periencesother maximum load pedal when and the linkage. A brake-reservoir bracket experiences maximum load when the

MAXIMUM LOADING FOR BRAKE-SYSTEM COMPONENTS Component

Maximum-Load Maximum Load on Component MAXIMUM LOADING FOR Condition BRAKE-SYSTEM COMPONENTS Panic stop-wheels locked 600 Ib forward 200 Ib side Maximum-Load Condition Maximum Load&on Component load on pedal pad. Brake pedal 8 Panic stop-wheels locked Ib forward & 200 Ib side Hydraulic system Panic stop-wheels locked 600 Calculated hydraulic linkage load on pedal pad. pressure with 300 Ib on pedal. Hydraulic system Panic stop-wheels locked Calculated hydraulic pressure Brake caliper Panic stop-wheels locked Calculated hydraulic pressure with 300 Ib on pedal. with 300 Ib on pedal. Brake caliper Panic stop-wheels locked Maximum Calculatedcalculated hydraulic brake pressure Caliper bracket Maximum deceleration with 300 torque . Ib on pedal. Caliper bracket Maximum deceleration Maximum calculated brake Brake rotor Maximum deceleration Maximum calculated brake torque. torque. Brake rotor Maximum deceleration Maximum calculated brake Fluid-reservoir Maximum bump & 5-g downward load & 2.5-g torque. bracket cornering side load on reservoir. Fluid-reservoir 5-g downward load & 2.5-9 Maximum bump 8 bracket cornering side load on reservoir.

Brake pedal & Component linkage

Formula car ran head-on into barrier with brakes locked. Forward-projecting master cylinders pushed bulkhead rearward and Formula car ran head-on into barrier with broke brake Forward-projecting pedal due to resistance of brakesoff locked. master driver's foot. Because of rearward severe and leg cylinders pushed bulkhead injuries, Indy Car prohibited broke off '85 brake pedal duerules to resistance of forward-mounted master cylinders. driver's foot. Because of severeLater leg rules prohibit mounted of injuries, ' 8 5 pedals lndy Car rules forward prohibited front-wheel centermaster line. forward-mounted cylinders. Later rules prohibit pedals mounted forward of

car hits acenter bump. front-wheel line.Assume that the

driver runs off the road and hi ts a car a The bump. Assume that the hard hits bump. bracket should be dedriver for runs off the road and hits signed similar maximum-load co n-a hard bump. The bracket should be desuspension and frame. dition as the signed for similar maximum-load This maximum-load condition is condifdition than as the and frame. ferent thesuspension maximum-load condiThis tion maximum-load for the brake condition pedal. Seeis difthe ferent than the maximum-load sample list of maximum loads condiin the tion for table. the brake See the above Writepedal. down the sample list of maximum loadsforin the maximum-load conditions all above parts table. Write the down system and calculate loads.the maximum-load conditions for all For all parts of the system receiving system partsthe andbrake calculate loads from fluid,the theloads. normal For all parts systemmaximumreceiving operating load ofisthe during loads from theSlamming brake fluid, the foot normal deceleration. your on operating load is during maximumthe pedal and locking the wheels does deceleration. Slamming your footInona 1101 give maximum-deceleration. the pedal and locking the wheels maximum-deceleration stop, does the not give maximum-deceleration. In a wheels are not locked, but the brakes maximum-deceleration the develop maximum torque. stop, The driver wheels but than the brakes pushes are lessnot on locked, the pedal he is develop of. maximum driver capable This is atorque. normalThe stop in a pushes less on the pedal than is race or a controlled fast stop onhethe capable of. This is a normal stop in a road. race a controlled fast stopmust on the All orbrake-system parts be road. made to operate properly at normal All brake-system be operating loads. And, parts they must must not made to operate properly atload normal breakwhile under maximum . operating loads. And, they must not Maximum Loads-Each car and car breakwhile under maximum load. designer will have different requireMaximum Loads-Each car ments for what loads to usecar for and designdesigner will have different requireing the brake system. I use the followments fordesigning what loadsa race to use for designcar: ing when

ing the brake system. I use the follow-

75-lb pedal force at maximum ing when designing a race car: deceleration- normal operating 75-lb pedal force at maximum condition; decelerationoperating 600-lb forward normal and 200-lb sideways condition; maximum force on pedal-panic-stop 600-lb forward and 200-lb sideways conditions.

maximum force on pedal-panic-stop conditions.

Exact values and loading conditions will vary from one car to another. Make sure you select the worst loading condition for each component-that is, the Exact values and loading conditions willNotice vary from car to condition another. Make condition most likely to cause a failure. that one the worst is notsure the you select the worst loading each component-that the same for each component in condition the brake for system. Hydraulic-system is, components condition mosttolikely to cause thethan worst is not are designed withstand 300aIbfailure. on the Notice pedal, that rather thecondition 600-lb load thethe same each component in the load brakeincludes system.aHydraulic-system for. The pedal factor for sudden components load pedal for is designed are designedwhich to withstand Ib on rather than the 600-lb load the application, does not300 apply to the the pedal, hydraulic system.

pedal is designed for. The pedal load includes a factor for sudden load application, which does not apply to the hydraulic system.

Factor of Safety-The maximum loads discussed in the previous section Factor of effects Safety-The maximum incl ude the of suddenly applied loads discussed the previous sectiona However,inthey do nol include forces. include the applied of effects safety.of suddenly As previously factor do not include forces. However, they factor discussed, the safety accountsa factor of safety.between As previously for the difference the maxidiscussed, factor mum load the on asafety part and its accounts breaking between for the difference strength. Never design a partthe to maxibreak mum load on a part and its breaking just as it reaches its maximum load. strength. design adesign part toisbreak Not evenNever an airplane that just as it reaches its maximum load. marginal. Not an factor airplane design for is that Theeven safety accounts unmarginal. knowns that cannot be calculated. Theis safety factor accounts unOne needed because parts for someknowns that cannot calculated. times have hidden flaws,bethey corrode One long is needed because parts someafter use, and loads are often diftimes tohave hiddenaccurately. flaws, they corrode ficult calculate after long use, and using loads are often difI recommend a factor of ficult to calculate accurately. safety of 3 on critical components. I recommend using a factor of This means that the breaking strength safety on critical of the of part3 should be atcomponents. least three This that the breaking strength timesmeans the maximum load on the part. of the part should be at least three You can test a part to see if it is strong times theifmaximum load ontothe part. enough, you can afford destroy You to see if test, it is strong one can part.test Ina apart breaking apply enough, if you afford toload destroy three times thecan maximum the one part. In a breaking test, apply part was designed for. If it doesn't three the amaximum load But, the break, times you have good design. part wasthedesigned it and doesn't destroy part afterfor. theIftest use design. abreak, brandyou newhave one aingood the car. The But, test destroy the part after the test and Reuse may have caused damage. amember, brand new in the Thetimes test you one tested it tocar. three may have load caused Rethe highest that itdamage. should ever member, you tested it to three times experience.

the highest load that it should ever experience.

Loads - Brake-system componen ts also are lo aded inertiaJly when the car Loads -Brake-system components is accelerating , decelerating, cornering alsohitting are loaded inertially the excar or bumps. Inertia when loads are is accelerating, decelerating, cornering pressed in g's. One g is an inertia load or hitting bumps. loads are exequal to the weightInertia of a part, assembly pressed One equal g is antoinertia load or car; 2ing g's. is a load two times equal to the weight of aI use part,the assembly the weight , and so on. follow2 gtoisdesign a load bracke equal to two structimes or ingcar; loads ts and the weight, and so on. I use the followtures that hold parts together: ing loads to design struc• Maximum bump brackets load = 5and g except turesoff-road that holdcars parts for or together: dirt-track racers. = 5 cars g except Maximum Use 10 g or bump more load for race that for off-road cars or dirt-track racers. normally hit large bumps. Use 10 g or cornering more for race thatg • Maximum load cars = 2.5 normally large bumps. on a car hit without wings or at speeds 2.5 g Maximum cornering below 100 mph. Cars load with= wings on a car without wings or at speeds above this speed will have higher below 100 mph. Cars with wings loads. above this speed will have • Maximum deceleration = higher 2.5 g loads. on a car without wings or at speeds Maximum deceleration = wings 2.5 g below 100 mph. Cars with on a carthiswithout or at speeds above speed wings will have higher below loads. 100 mph. Cars with wings above this speed will have higher acceleration = 2.0 g on • Maximum loads. all cars except dragsters. Use 5.0 g or Maximum acceleration = 2.0 g on higher for dragsters. allOn carssmall exceptparts dragsters. 5.0 g or such Use as brackets higher forother dragsters. holding parts to the frame, viOn small such as Abrackets bration must parts be considered. small, holding other parts to the frame, vilightweight part is subjected to higher A small, bration must considered. vibration loadbe s than a large, heavy lightweight is subjected higher part. The part amount of to vibration vibration onloads than a large, heavy depends engine design , suspension part. The amount of vibration stiffness, engine mounts , road

depends on engine design, suspension stiffness, engine mounts, road 91

Maximum loads can occur in two directions at once. Here, stockcar driver cuts a close apex. Resulting bump load from going over curb on right front wheel occurs same timeatasonce. maximum Maximum loads can occur in twoatdirections Here,cornerstocking load. car driver cuts a close apex. Resulting bump load from going over

curb on right front wheel occurs at same time as maximum cornering load.

surface, and many other factors. If in doubt , design small parts to withstand surface, many other If in twice theand maximum loadsfactors. just given. doubt, design small to withstand If anything falls offparts the car, increase twice the maximum its design load when loads doing just the given. repair. If anything falls off the car, increase The only way to measure vibration its design loadexpensive when doing the repair. loads is with sophisticated The only way to measure vibration equipment, which most people can't loads is with expensive sophisticated afford .

equipment, which most people can't afford. CALCULATING TIRE FORCES

To start a brake-system design , first CALCULATING determine forces TIRE acting FORCES on the tires To start aa brake-system first during stop at design, maximum determine forces onthe theeffects tires deceleration. This acting includes during a stoptransfer at and maximum of both weight aerodeceleration. This includes the effects dynamic forces on the car. To do the of both transfer and some aerojob right, weight you need to know dynamicfacts forces ont the thecar: car. To do the specific abou job right, you need to driversome and • Weight of car includingknow specific facts about the car: other loads. of car including driver and • Weight Wheelbase length. other loads. • CG height and fore-and-aft Wheelbase length. location . G height fore-and-aft • C Maximum tire gr and ip. location. • Aerodynamic forces on body. Maximum grip. almost completely A car has tire to be Aerodynamic on body. designed before forces this information can car has to accurately. be almost completely be Adetermined Therefore, designed before this information all the above information may notcan be be determined accurately. Therefore, available at the time the brake system all first the above information may notyou be is designed . Consequently, available at theassumptions-educated time the brake system must make is first designed. you guesses. Start by Consequently, making the brake must make assumptions-educated system adjustable if you don't start guesses. Start byinformation. making the Later, brake with accurate system car adjustable during testing, if youyou candon't makestart adwith accurate information. justments to the brake system . Later, during carThe testing, youof can make adWeightweight a car greatly justments the brake system. affects thetobrake-system design. The

Weight-The weight of a car greatly affects the brake-system design. The

92

Toughest type of vehicle to maintain brake balance under all loading conditions is nose-heavy, front-wheel-drive pickup. Loadsensing proportioning valve between brake body balance and rear under axle ofallDodge Toughest type of vehicle to maintain loadRampage adjusts so brake balance is maintained under all ing conditions is brakes nose-heavy, front-wheel-drive pickup. Loadload conditions. sensing proportioning valve between body and rear axle of Dodge

Rampage adjusts brakes so brake balance is maintained under all load conditions.

car will have to stop in its heaviest form, traveling at m aximum speed. If car will ishave to stoptheincalculation its heaviest the car for racing, is form, traveling at maximum speed. If easy. Most race cars have nearly a conthe carweight is for racing, is stant except the for calculation fuel weight. easy. Most race cars have nearly a conSo , design race-car brakes assuming stant weight full fuel load. except for fuel weight. So,Ondesign race-car brakes assuming a road car, weight can vary full fuel load. The hardest vehicle to considerably. On abrakes road for car, isweight canTrucks vary design a truck. considerably. The hardest vehicle to weigh much more fully loaded than design brakes for is a truck. Trucks when empty. In addition , their centers weigh much more fully when loaded than. of gravity move greatly loaded when empty. In addition, their centers The design of a brake system for such gravityshouId move be greatly aofvehicle basedwhen on itsloaded. maxiThe design of a brake system such mum weight. However, brake for balance amust vehicle be basedaton the its maxibeshould considered nomum weight. However, balance load/full-load extremes .brake Unless the must has be anconsidered at the notruck adjustable brake balance load/full-load extremes. Unless the or a special anti-skid device , balance truck probably has an adjustable brake balance will be incorrect when or a special balance empty. Mostanti-skid trucks device, lock the rear will probably be incorrect when wheels under hard braking if reasonaempty. Most trucks lock the rear bly well balanced when loaded . wheels under -CG hard braking reasonaCG Location location ifcan be esbly well balanced whenwith loaded. timated or calculated reasonable CG Location-CG location be esaccuracy. Most sedans arecanslightly timated or calculated with reasonable nose-heavy when empty and closer to accuracy. Most sedans are slightly 50/50 weight distribution when fully nose-heavy when empty and closer to loaded. This puts the CG at the mid50/50 weight distribution when fully point of the wheelbase at full load. loaded. This puts the sports C G at cars the midThe majority of road also point 50/50 of theweight wheelbase at full Most load. have distribution. The majority road sportswith cars drag also race cars are oftail-heavy, have 50/50 weight distribution. Most racers being the most tail heavy and race cars draga stock cars are the tail-heavy, least. You with can get racersfeel being the most and good for weights andtail CGheavy locations stock cars the least. You can get from automotive-magazine road tests.a good for weights and CG locations CGfeel height is harder to guess at. from automotive-magazine tests. Most sports-car CGs areroadslightly

CG height is harder to guess at. Most sports-car CGs are slightly

above wheel center. A race-car CG is lower than on a road car. If you know A race-car CGare is above wheel where all the center. heavy parts of the car lower than a road car. IfCG you height know located, youoncan calculate where all the heavy parts ofBut the, car are with reasonable accuracy. if you located, you can calculate CG height don't know where they are, it is probawith reasonable you bly too soon toaccuracy. design But, the ifbrake don't where the theycar are,design it is probasystemknow . Establish first, bly design brake then too comesoon back to to the brake the system . system. Establish simple the car chart designcan first, As illustrated, be then back to the system. used come to calculate CGbrake location. Find illustrated, simple can be theAsweight of each majorchart component used to calculate CG location. Find of the car and its planned CG location the weight from of each component measured the major ground and disof the from car and planned CG location tance theitsfront-axle center line. measured from the ground and Multiply the weight times dis-a tance from thelong front-axle distance-as as it'scenter from line. the Multiply the write weight times ina same point-and the number distance-as longcarasweight it's seems from too the the chart. If total same point-and write the number in low , you left out something. Miscellathe chart.small If totalitems car weight neous are seems hard too to low, you left out something. estimate. However, try to Miscellaestimate neous small when items designing are hard the to their weight estimate. However, try toliquids estimate brakes. Also, don't forget and their weight whenof designing the people. The sum the individual brakes. Also, don't forget liquids and weights is obviously tota l car weight. people. sum of the The sumThe of the weight timesindividual distance weights is obviously totalweight car weight. column divided by total gives The sum of the weight times distance CG location. column divided by weight gives Tire Grip-Tire griptotal is important. It C G location.maximum deceleration of determines Tire Grip-Tire grip is important. It the car. On a car without aerodynamic determines maximum deceleration of downforce , maximum deceleration of the car. a carmaximum without aerodynamic the car On equals tire friction downforce, On maximum deceleration of a car with aerodynamic coefficient. the car equals maximum tire friction downforce, deceleration is higher. coefficient. a car with aerodynamic Tire grip On varies considerably. Road downforce, deceleration higher. condition is as importantis as the tires Tire grip varies Road themselves. Racingconsiderably. tires on dry pavecondition as important the tires ment can ishave a grip ofasover 1.0 .

themselves. Racing tires on dry pavement can have a grip of over 1.0.

Component Engine Component Transmission Engine Driver Transmission Front wheels/tires Driver Rear wheels/tires Front wheels/tires Front suspension Rear wheels/tires Rear suspension Front suspension Front brakes Rear suspension Rear brakes Front Framebrakes Rear Body brakes Frame Fuel tank Body Radiator & water Fuel tank Battery Radiator Pedals 8, water Battery Seats

W

x

(WX)

y

(WY)

W

X

(WX)

Y

(WY)

Pedals Seats

Totals

W(total) -

Totals

W(total)

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ｾ＠

-

WX(total) -

WX(total)

(WX) total CG X~~ == (WY) total Y W total CG (WY) total W= each compoment in Y~~ = X = distance CG W totalof component CG from front-wheel inches = weight center of eachincompoment in pounds W 'CG Y= = distance height of of component CGCG from the ground in inches X component from front-wheel center in inches XCG = CG location behind front-wheel center in inches = height of component frominthe ground in inches Y Y CG = CG location above CG ground inches XCG= CG location behind front-wheel center in inches = CG location above ground in inches ,Y ,

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WY(totail :

WY (total)

YCG Ground

t

Ground

CG location can be determined by filling out chart and performing calculations. Each component in a car has its own weight and CG location. List weight and CG location for each component If component is out forward front-wheel center, use a negative CG location can as beshown. determined by filling chartof and performing calculations. Each number for X-in thishas case times X will negative. forlocation WX, make component in a car its W own weight andbeCG location.When List adding weight totals and CG for sure you add negative numbers correctly orisWX total will be too large. center, use a negative each component as shown. If component forward of front-wheel number for X-in this case W times X will be negative. When adding totals for WX, make sure you add negative numbers correctly or WX total will be too large.

Road tires seldom exceed 0.8. You'll have to choose the tires before you Roadestimate tires seldom exceedgrip. 0.8. If You'll can maximum you have to the tires before guess toochoose high, weight transfer willyou be can estimate maximum grip. If you too high. guess too high,Forces-Most weight transfer willcars be Aerodynamic race too high. quickly at high speed bedecelerate Aerodynamic Forces-Most racefrom cars of aerodynamic downforce cause decelerate quickly at high speed bewings and the shape of the body. cause of aerodynamic downforce from Downforce varies with car design and wings the that shape of huge the wings body. speed. and On cars have Downforce withdownforce car design may and or ground varies effects, speed. On cars that have huge wings exceed the weight of the car! or ground effects, may Consequently, you downforce should know exceed weight of thebefore car! somethingtheabout downforce Consequently, brakeshould system. know First, you can design ayou something before the supplier about of your downforce wing(s) should be you a brake system. inforFirst, able can to design give you downforce the supplier of youronwing(s) should be mation. However, a ground-effects able to give you downforce inforcar, testing in a wind tunnel is usually mation. However, on a ground-effects the only way to get this information. car, testing in a wind anything tunnel is by usually You can't estimate just the onlyatway to get this information. looking the car. You estimate anything by just At can't highway speed, aerodynamic looking are at thesmall. car. So ignore aeroforces At highway speed, aerodynamic dynamic forces on a road car unless forces are small. So ignore aeroyou have accurate information.

dynamic forces on a road car unless you have accurate information.

Again, be ready to change the brake system during testing if things don't Again,as be to change the brake work youready estimated . system during totesting if things In addition the amount of don't aerowork as you estimated. dynamic force, you must know where In force addition of aeroon the the amount body. The point this acts to dynamic force, you must know where where the center of all aerodynamic this force the body. point forces actsactsis oncalled the The center of where the allcenter aerodynamic pressure. Oncenter a wing of , the of presof forcesis acts is called theof center sure roughly a fourth the way pressure. a wing, center of wing pres-. front the edge of the back fromOnthe sure fourthbeofanywhere the way. On a is carroughly body, ita could back from the front edge of the wing. If you don't have any information, On a car body, it could be anywhere. assume the center of pressure is at the If you don't center of have the any bodyinformation, - not the assume the center of is at the wheelbase. Designingpressure a ground-effects center of testing the tobody-not the car without find the center wheelbase. a ground-effects of pressureDesigning may cause big trouble . car without testing to findonthegroundcenter Many handling problems of pressure may cause big trouble. effects cars have been caused by a Many handling problems center of pressure being inonangroundunexeffects cars have been caused by a pected place. center pressure being in anwith unexAdd Upofthe Numbers-Now, all pected place. the estimated weights or loads, calcuAdd tire Up the Numbers-Now, all late forces. To make life with simple, the estimated weights or loads, calcuassume that friction force on a tire late tirevertical forces.force To make lifegrip. simple, equals times its For

assume that friction force on a tire equals vertical force times its grip. For

a tire with 1000 Ib of vertical force on it and a grip of 0.8, friction force is a tirelb.with 1000 Ib were of vertical on 800 If the grip raisedforce to 1.1, i t and grip ofdeliver 0.8, friction is that tirea could 1100 lb force of fric800 lb. If the were force raised istowhat 1.1, Thegrip friction tion force. that tire deliver lb high of fricstops thecould car-it should1100 be as as tion force. The friction force is what possible. stops car-it page should as high as See the drawing, 94,bethat shows possible. the forces acting on a car during See drawing, 94, that shows braking. For this page calculation, I assume the forces acting on a car during the right and left tires at both ends of braking. For loaded this calculation, assume the car are equally. IThis asthe right and left tires at both ends of sumption is more accurate than other the car are loaded equally. This asdata usually used for this calculation. sumption is more accurate than other The formulas with the drawing are data usedtire for forces this calculation. used usually to calculate . If you are The formulas the drawing are assuming somewith aerodynamic lift, put used to calculate tire forces. If you are a negative number into the formula assuming some aerodynamic lift, put for downforce . a When negative numbera car intoto the designing run formula on varifor downforce. ous surfaces or different types of tires, When the designing car to accordingly. run on varichange grip avalue ous surfaces or different types of tires, Then perform a calculation for each change the grip value accordingly. grip. Grip might be as low as 0.3 for a Then performto aperhaps calculation for aeach 1.4 for hot slick surface grip. low .asResulting 0.3 for a racingGrip tire might on a be dryastrack slick surface to the perhaps for forces a hot answers will be range 1.4 of tire racing tire on a dry track. Resulting you must deal with.

answers will be the range of tire forces you must deal with.BRAKE TORQUE CALCULATING

Brake torque is the friction force on CALCULATING BRAKE TORQUE the tire, multiplied by the rolling Brakeoflorque is the friction on radius the tire. For designforce of the the tire, multiplied by the rolling brake system, always use maximum radius the tire.Maximum For design torque of the brake oftorque. brake when: system, always use maximum occurs brake torque. torque • Vertical force onMaximum tire is maximum . occurs when: • Tire grip is maximum. Vertical force on tireare is maximum. tires used. • Largest-radius Tire grip is maximum. • Car is stopped at maximum possible Largest-radius tires are used. deceleration. Car possible If a is carstopped has a at nutmaximum on the center of deceleration. each wheel, you could measure brake If a car hasa a large nut on the center of torque with torque wrench. each you on could Whilewheel, pushing themeasure brake brake pedal torquean with large torque with efforta needed to givewrench. maxiWhile pushing on the pedal mum deceleration, turn brake the wheel with an effort give maxiwith the torqueneeded wrenchtoand measure mum deceleration, turnEven the though wheel torque as the wheel turns. with the torque wrench and measure this test is done rarely, this example iltorque aswhat the wheel Even though lustrates braketurns. torque means. A ilthis test is donemust rarely, brake system be this ableexample to deliver lustrates what braketorque. torqueOtherwise, means. A the needed brake brake system must be able to deliver the driver won't be able to stop the the needed brake torque. Otherwise, car at maximum deceleration with an the driver won't be ableHe to may stop not the acceptable pedal effort. car maximum an haveat the strengthdeceleration to achievewith maxiacceptable pedal effort. He may not mum deceleration' have the strength to achieve maxiCalculate maximum brake torque mum using deceleration! the formulas given . Use the Calculate maximum brake values of grip, car weight andtorque aerousing the formulas given. Use the dynamic force that give maximum values offorce grip,oncarthe weight aerofriction tire. and Calculate

dynamic force that give maximum friction force on the tire. Calculate 93

Modern cars with wings and ground effects generate much more downforce than ordinary cars. Indy Car cornering and braking loads arecars much higher than forground a modified roadgenerate car. You much must know Modern with wings and effects more speed and downforce to correctly calculate loads generated by downforce than ordinary cars, lndy Car cornering and braking tires. loads are much higher than for a modified road car. You must know

speed and downforce t o correctly calculate loads generated by tires.

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Center of

Design of ground-effects car should be left to experts. Windtunnel testing is the only sure way to determine aerodynamic loads Note ground-effects at rear of car. Designonof car. ground-effects car shouldexit be tunnels left to experts. WindPhoto by Tom Monroe. tunnel testing is the only sure way t o determine aerodynamic

loads on car. Note ground-effects exit tunnels at rear of car. Photo by Tom Monroe. I

wheelbase of car (in.)

=

We = total weight 01 the car (lb) F, vertical force on (in.) both front tires (Ib) I == wheelbase of car force of onthe both F,, = =vertical W total weight carrear (Ib)tires (lb) FA = vertical aerodynamic downforce Ff = force on both front(lb) tires (Ib) f-t (coeflcient friction) tires F, == grip vertical force onofboth rear of tires (Ib) d = aerodynamic maximum deceleration FA downforce(g's) (Ib) M= from front axle to center b = p = distance grip (coeffcient of friction) of tires of pressure (in.) Xeg = maximum distance from front axle(g's) to CG (in.) dM = deceleration Y height offrom CG above ground (in.) of pressure (in.) b eg = -distance front axle to center Xcg = distance from front axle to CG (in.) Ycg - height of CG above ground (in.) [Xeg f-t Y･ｾ＠ f.1. YegJ F, = ｗ･ｾ＠ --1- + -I-J+ FAL + --I-

[b

,

2FFR

__-

-I

=

w,[-p + 'j++ F] FA[-:

_ _ Xcg _ _ _ _...... 1 We

I

I-

I

Fr = W,

.1

+ FA- Ff

I

FF = Friction Force On One Front Tire ］ｾ＠ LIL

FF

=

d M = ~ +FAP -

wc

f-t F,

Friction Force On One Rear Tire = - -

2

vFf

2

/JFr

FF = Friction Force On One Front Tire =FF =on Friction Forcetire On One Rear Tire =forces - are computed. If you can estimate or calculate all data shown on drawing, 2you can calculate forces tires. From forces, friction 2 Friction forces are then used to calculate brake torque during maximum deceleration. It is assumed FA is the only aer?dynamic downforce.

If you can estimate or calculate all data shown on drawing, you can calculate forces on tires. From tire forces, friction forces are computed. Friction forces are then used t o calculate brake torque during maximum deceleration. I t is assumed FAis the only aerodynamic downforce.

both front- and rear-tire forces. Maximum brake torque is calculatboth and rear-tire forces. ed byfrontthe following formulas: Maximum brake torque is calculatFront-brake torque = FFF r FT in ed by the following formulas: i nCh-pou nds Front-brake torque rFTtire in in FFF = Friction force = onF,front inch-pounds pounds Frictionradius force on front tire tire inin FFF r FT == Rolling of front pounds inches

,r = Rolling radius of front tire in Rear-brake torq ue = FFRr RT in inches

inch-pounds Rear-brake torque in in FFR = Friction force=onFF,rrear tire inch-pounds pounds F Frictionradius force on rear tire tire inin r,RT == Rolling of rear pounds inches

,,r = Rolling radius of rear tire in Rolling Radius - The rolling radius of inches

a tire is the distance from the center Rolling Radius rolling radills of of the wheel to -The the pavement wilh the a tire is the distance from the center of the wheel to the pavement with the

94

lire loaded. You cannot get an accurate rolling radius by measuring an unloadtire tire. loaded. Youtirecannot get an accurate ed The deflects when suprolling porting radius a car. by measuring an unloaded Rolling tire. The tire depends deflects on when radius the supload porting a car. on the tire, tire size, inflation pressure radius the load andRolling stiffness of depends the tire on casing. So on the tire, tire size, inflation pressure measure rolling radius with the car on and stiffnessMake of the the ground. suretirecarcasing. weight So is measure rolling radius with the on the same as yours will be. Also car check the ground.pressure; Make surecorrect car weight inflation it is if the same as yours will be. Also check necessary. inflation pressure; correct it if necessary. SELECTING & POSITIONING BRAKES SELECTING & Take the following into consideraPOSITIONING BRAKES tion before selecting brakes: following • Take Disc orthe drum brakes. into consideration before selecting brakes: Disc or drum brakes.

• Brake diameter. • Brake mounting-inboard or outBrake diameter. board. Brake mounting-inboard outEach decision must be madeorbefore board. a brake . selecting Each be made Theredecision are a must number of before brake selecting a brake. sources. Several manufacturers have Thereforarespecial a number of brake brakes applications. Or, sources. Several have you could use manufacturers standard road-car brakes for special applications. Or, brakes. Your choice depends primarily you could use standard road-car on the intended use. For instance, is brakes. choiceuse depends primarily your carYour for street or racing? If it's the intended Fordesigned instance,for is aonrace car, use use. brakes it's your for street or racing? racing.carBrakes fromuse a road car areIfusua racetoo car, heavy use brakes for ally for designed best racing racing. Brakes from a road car are usuperformance. And racing brakes on a ally too racing street car heavy may be foran best unnecessary performance. And racing brakes on a expense. street car may be an unnecessary expense.

Unloaded Radius of Tire Unloaded Radius Tire at Proper Inflation Pressure and Load Tire Under at Proper Inflation Pressure and Under Load

While most road-car brakes are too heavy, some are worth considering for highperformance use. Cast-iron Corvette While most road-car brakes1984 are too heavy, sliding are caliper was designed more high some worth considering forforhighperformance thanCast-iron low cost.1 9It8 4may be a performance use. Corvette natural for road with 4-wheel sliding caliper was car designed more for disc high brakes. Photo than courtesy performance low Girlock cost. ItLtd. may be a natural for road car with 4-wheel disc brakes. Photo courtesy Girlock Ltd. Ｍｾｲｇｯｵｮ､＠

F = Vertical Force on Tire = Vertical Force on Tire from wheel center to ground with car weight on tire. Tire RollingF radius of tire is distance must be at correct inflation pressure. Rolling radius of tire is distance from wheel center to ground with car weight on tire. Tire must be at correct inflation pressure.

Disc Brakes or Drums? - Because disc brakes are usually superior to Disc Brakes Drums? -Because drum brakes, or most people choose disc brakes are usually superior to discs for high-performance applidrum brakes, mostthere people cations. For racing, is nochoose other discs for high-performance applichoice if you want to win. Drum cations. For racing, there is no brakes have many limitations. other You choice want to to win. will needif a you special reason use Drum drum brakes have many limitations. You brakes for racing-such as rules requir-

will need a special reason to use drum ingthem. requirbrakes racing-such as rules of On a for road car, a combination disc ing them. and drum brakes may be best. Drums Onbe a road car, aon combination of disc may standard the rear axle you and drum brakesroad may cars be best. mustDrums have will use. Also, may be standard on theare rearusually axle you parking brakes- drums set will use. Also, road cars must up for parking brakes. Although have disc parking brakes-drums are usually set brakes on the rear are good for a road up for parking brakes. Although disc car, they may introduce added combrakes rear Aaredisc good for athat's road plexity on andthecost. brake car, they mayforintroduce not designed a parkingadded brakecommay plexity andtocost. be difficult adapt.A disc brake that's notNow designed for posed a parking brake may that I've the disc/drumbe difficult to adapt. brake question, I'll assume you are Nowdisc that brakes I've posed discldrumusing on allthefour wheels. brake high-performance question, I'll assume Most cars you are are so using disc brakes on all four wheels. designed. If you choose drum brakes, Most high-performance cars areThe so the design procedure is similar. designed. Ifis you brakes, difference thatchoose you'll drum have to conthe design procedure is similar. The sider the servo action of a drum difference is that you'll have to conbrake. Servo action is discussed in sider the2. servo action of a drum Chapter brake. Servo action is discussed in Brake Diameter-Disc-brake diameChapter 2. outside diameter of the ter is the Brake Choose Diameter-Disc-brake diamerotor. the largest-diameter ter is the outside diameter the brakes that will fit in the wheels,ofif the rotor. Choose the inlargest-diameter brakes are mounted the wheels, not brakes that will98. fit The in theonly wheels, if the inboard, page exception brakes are mounted in the wheels, not inboard, page 98. The only exception

to this is on a very light car or one with large-diameter wheels. Most to this is on a very light car or from one high-performance cars benefit with large-diameter the largest possible rotorwheels. that will Most fit. high-performance benefit from Maximum rotor cars diameter is about the largest possible rotor that will fit. 3-in. smaller than wheel diameter. Maximum diameter is about For example, rotor a IO-in. rotor should go 3-in. than wheel diameter. inside smaller a 13-in. wheel or a 13-in. rotor For example, a 10-in. rotor should go in a 16-in. wheel. Caliper design deterinside a 13-in. wheel or a 13-in. rotor mines how big a rotor can be used for a 16-in. wheel. Caliper design deterwheel. aingiven mines how big a rotor canuse be used for For pavement racing, a largea given wheel. diameter wheel with a low-profile tire For than pavement racing, rather a smaller wheeluse andaa largehighdiameter wheel with a low-profile tire profile tire. With a given rolling rather than a smaller wheel and a highradius, the large wheel allows the use profile tire.brake Withrotor; a given of a larger and therolling lowradius, the corners large wheel profile tire better.allows the use of a larger brake rotor;- and the lowDisc-Brake Selection Rotors and profile tire corners better. calipers should be selected as a Disc-Brake and matched set. Selection By using -aRotors caliper and calipers shouldto be rotor designed workselected together,asyoua matched set.to By usingabout a caliper and don't have worry a dimenrotor designed to work together, you sional mismatch between the two. So don't have to worry dimenchoose the caliper andabout rotor aintended sional the two. So for themismatch same roadbetween car or from a racechoose the caliper and rotor intended car- brake manufacturer. forCalipers the same car or from a raceandroad rotors must meet the car-brake requirements: manufacturer. following and be rotors mustenough meet the • Calipers Rotor must massive to following requirements: absorb heat from at least one stop Rotor must be speed massive to from maximum at enough maximum absorb heat from at least one stop vehicle weight. from maximum speed and caliper mustatfit maximum mounting • Rotor vehicle weight. space on car. Rotor and caliperdeliver must fit maximum mounting • Brake must space car. required without excesbrake on torque

Brake must deliver maximum brake torque required without exces-

Although fixed, aluminum race-car caliper appears similar to Corvette caliper in above photo. APaluminum CP2751 race-car caliper was deAlthough fixed, caliper Signed forsimilar IMSA toroad racers using appears Corvette caliper13in in.-diameter above photo.rotors. AP C PThese 2 7 5 1 require caliper minimum was de14-in.-diameter inboard brakes. signed for IMSAwheels road or racers using 13Photo courtesy AP Racing. in.-diameter rotors. These require minimum 14-in.-diameter wheels or inboard brakes. Photo courtesy AP Racing.

Race cars generally use largest possible brake diameter. On this Indy Car, caliper almost rubs generally against inside wheel.possible Race cars use of largest brake diameter. On this lndy Car, caliper almost rubs against inside of wheel.

sive tl uid pressure. One-Stop Temperature Rise Roadsive pressure. weight must be Car fluid Rotors-Rotor One-Stop Temperature Roadhigh enough to absorb Rise all kinetic Car Rotors-Rotor weight must be energy stored in the moving car. The high enough absorb all worst conditiontois stopping a carkinetic travenergyatstored in thewith moving car.atThe eling top speed the car its worst condition is stopping a car maximum weight. Some road travcars eling at top that speedprobably with thedon't car at its have brakes meet maximum weight.This Some road cars this requirement. is probably be-

have brakes that probably don't meet this requirement. This is probably be95

Kinetic energy

Wc S2 =---

W,S2 29.9 Kinetic energy =in foot-pounds 29.9 We = Weight of car in pou nds Sin =foot-pounds Speed of car in miles per hour W, = Weight of car in pounds After calculating kinetic energy S = Speed of car inthe miles per hour of a car, determine how much energy After kinetic goes to calculating the front the brakes andenergy how of a car, determine how much energy much to the rears. A good guess is to goes to thekinetic front energy brakes according and how proportion much the torques. rears. A This goodrelationship guess is to to the to brake proportion kinetic energy is only approximate, but theaccording calculato the brake torques. This tion for rotor weight does relationship not have to is but the calculabe only exact.approximate, Use the following formula:

tion for rotor weight does not have to KrTF = K exact. be Use the following formula: F

Exception to the rule: Brake is considerably smaller than wheel allows on front ofI lu sprint car. Demands on Brake brakesisofconsideracar raced Exception to the rule: on are than muchwheel less allows than ifonraced bly dirt smaller front on of pavement. sprint car. Demands on brakes of car raced on dirt are much less than if raced on pavement.

Garage area or pits is best place to look at and photograph race-car brakes. Take advantage of oryears trialGarage area pits isof bestexpensive place to look at and-error development to select and photograph race-car brakes. Takerotor adsizes and of designs. the mechanics. vantage yearsTalk of toexpensive trialIf they have brake trouble, their and-error development to consider select rotor problems your Indy sizes and during designs. Talkbrake to thedesign. mechanics. Car brake wasbrake photographed at Phoenix InIf they have trouble, consider their ternational Raceway-one-mile problems during your brake design.paved lndy track that was putsphotographed high demands on brakes. Car brake at Phoenix InPhoto by Tom Raceway Monroe. -one-mile ternational paved

track that puts high demands on brakes. Photo by Tom Monroe.

cause some road-car designers think it's unreasonable to drive at the top cause some designers speed of a carroad-car at maximum weightthink and it's unreasonable drive at thethink top suddenly do a hardtostop. I don't speed of a car at maximum weightdrivand it's unreasonable, even though suddenly a hard think ing at topdo speed is stop. illegalI don't and unsafe it's unreasonable, even though on the road; but some people do it.drivingFrom at top speed 1, is the illegal and energy unsafe Chapter kinetic on the road; but some people do it. as of a moving car is determined From Chapter 1, the kinetic energy follows:

of a moving car is determined as follows: 96

(T F + T R)

KF = Kinetic energy to front brakes in foot-pounds KF = Kinetic energy to front brakes Kr = Total kinetic energy of car in in foot-pounds KT Total kinetic energyinofinch-pounds car in T F == Front brake torque foot-pounds T R = Rear brake torque in inch-pounds T, = Front brake torque in inch-pounds = Kr - KF = Rear brake torque in inch-pounds T , KR KR = Kinetic energy to rear brakes in K,= K T - K, foot-pounds K, = Kinetic energy to rear brakes in The kinetic energy calculated is for foot-pounds a pair of brakes-two front and two TheDivide kineticthe energy calculated for rear. answers by 2 tois get pair of brakes-two and two akinetic energy absorbed front by each brake. rear. Divide the answers by 2 to rise get Now, compute the temperature kinetic energy absorbed by each brake. of the rotor after one stop using Now, compute formula on page the 11 .temperature Use weightrise of of therotor rotoror after stop using single drum one for W s' This is formula on temperature page 11. Use of the average of weight the entire single rotor drumtemperature. for W,. This is rotor, not theor surface theIfaverage temperature of the entire the average rotor temperature is+ rotor, the surface near not lOOOF (538C) temperature. use a heavier If the average temperature rotor. This meansrotor a thicker rotor is if near lOOOF (538C) use a you have chosen the largestheavier rotor rotor. This means The a thicker rotor if diameter possible. type of brake you have the largest linings usedchosen will determine howrotor hot diameter The still type have of brake the rotor possible. can be and the linings used will determine how hot brakes work. the rotor Rotors-If can be andyou stillarehave the Race-Car designbrakes work. ing a race car, and the brakes are used Race-Car Rotors-If designmany times during a you race,are a calculaing a race car, and the brakes are used tion for one stop will not mean much. many times a race, a calculaBefore each during stop, brake temperature tion be formuch one stop willthan not mean much. will higher 100F (38C). Before each stop, brake temperature For a road racer, assume the rotors will much500F higher(260C) than 100F ( 3 8the 0. are be about when For a road racer, assume the rotors brakes are applied. Also, each brake are about is500F (260C)topwhen application not from speed the to brakes are applied. Also, each brake full stop as assumed in the previous application is not from top speed to calculations. fullRacers stop ashave assumed in the previous experimented with calculations. different-size and -weight rotors for Racers have experimented with years. Although some work, others different-size -weight for can overheat. and After years rotors of trialyears. Although others and-error, a brake some designwork, has been decan overheat. Afterracing yearsclass of trialveloped for each that

and-error, a brake design has been developed for each racing class that

works for most cars under normal conditions. Go to the track and look at works for on most under normal the brakes carscars similar to yours. If conditions. G o selected to the track and lookdifat the rotor you is greatly the brakes on cars to yours. If ferent in size andsimilar weight, you are the rotor you selected is greatly difprobably wrong. If in doubt, go larger. ferent size and weight, you onarea Use thisinmethod to select rotors probably wrong.your If incar doubt, go larger. race car, unless is unique. Use thisword method to selectIfrotors One of caution: other on carsa race car, unless your car is unique. in your class are using water-cooled One word of147 caution: other have cars brakes-page -they Ifeither in your classrotors are using water-cooled undersized or improper air brakes-page ducting. Water 147-they cooling is aeither crutchhave and undersized or unless improper air should not rotors be used larger ducting. Water cooling is a. crutch and brakes cannot be fitted In other should notthebecompetition used unlessis larger words, if using brakes cannot be In thicker other water cooling, go to afitted. larger or words, if they the use. competition is using rotor than water cooling, to ayou larger thicker While at the go track, canormake inrotor than observations they use. teresting about brakes. at the canoval make inIf While you are at atrack, flat, you paved track teresting about brakes. where hardobservations braking is used going into If youone areand at athree, flat, time pavedvarious oval track turns cars where hard braking is used going early in a long race and late in into the turns one time increase various cars same race.and If three, lap times on early in longnot race latechances in the some carsa and on and others, same lap times increase on are therace. cars Ifrunning slower near the some cars and not on others, chances end are "running out of brakes." See are carsvarious running cars slowerarenear the whatthethe doing end are "running out of brakes." See differently. what carslong arestraights doing At a the road various course with differently. followed by tight turns, such as turn Atata road course withthelong straights five Elkhart Lake, importance followed by tight turns, such turn of good brakes is evident. Walkasalong five at Elkhart the straight to Lake, where the theimportance cars start of good brakes is evident. Walkdeeper along braking and see how much the straight to where the cars start cars with good brakes go. Good braking andmean see ashow much brakes can much as a deeper 200-ft cars with going goodinto brakes Good advantage a slowgo. corner off brakes can mean as much as a 200-ft a fast straight. Imagine how much advantage a slowitcorner horsepowergoing and into handling takes off to amake fastupstraight. 200 feet!Imagine how much horsepower and handling it takescan to Race-ear-brake manufacturers 200 feet! make up be a big help when selecting rotors for Race-car-brake can a race car. They aremanufacturers aware of all applibe a big for helptheir whenproducts selecting and rotorswhat for cations a race car. aware of all aware appliworks best.They Theyare also are made cations for their their brakes productsdon't and work. what of it when works best. They also are made aware Manufacturers work with race-car deof it when brakes signers to their develop the don't best work. rotor Manufacturers work with design for each racing class.race-car designers to companies develop the rotor Contact suchbest as Hurst, design for each racing class. JFZ, Tilton, Wilwood or their dealers Contact suchyour as special Hurst, before you companies buy rotors for JFZ, Tilton, Wilwood or their dealers race car. before Area-Another you buy rotors for special Swept aid your in selecting race car. the proper rotor size is the swept area Swept aid on in selecting of the Areabrake. Another The chart page 28 swept cars. area the proper rotor sizefor is the shows swept area various of the brake. The chart on page 28 Consider using a swept-area-to-weight shows swept area for various cars. ratio for a car of nearly the same Consider a swept-area-to-weight power andusing speed as yours. If you are ratio for aa car nearly same designing raceofcar, use the a swept-

power and speed as yours. If you are designing a race car, use a swept-

area-to-weight ratio for race cars, not for road cars. In both cases, if long area-to-weight race cars, not lining life andratio fadefor resistance are for road cars. In both cases, if long more important than brake weight, lining life and use a higher sweptfade area. resistance are more important thanmeans brakeyou weight, Higher swept area must use swept area.rotor. This may use aa higher larger-di ameter Higher sweptusing area means you must mean larger-diameter also use a larger-diameter rotor. Thisrotor may wheels, if the wheels limit also meanIf you usingsimply larger-diameter diameter. cannot get wheels, if the area wheels limit ofrotor enough swept because the If you simply diameter. wheels, you can reso rt tocannot using get inenough swept page area 98. because of the board brakes, An inboard wheels, can resort to using inbrake isyou mounted inboard on the board or brakes, page transferring 98. An inboard frame transaxle, brakinboard onto the brake is through mounteda driveshaft ing force the frame or transaxle, transferring brakwheel. ing force a driveshaft the Vented or through Solid Rotors - When to lookwheel. ing at cars like yours, note whether Vented ororSolid vented solidRotors-When rotors are lookused. ing at cars likeweight yours,and note whether Usually, rotor cooling revented or solid rotors ifare vented used. quirements determine Usually, weight and cooling rerotors arerotor needed. Vented rotors are quirements determine if needed. vented rotors are used where heavier rotors needed. Vented are A very are thick solid rotor doesrotors not cool used where heavier rotors are needed. adequately. Because of this, it is A very thick solid cool unusual to see a rotor solid does rotor not thicker adequately. than 1/2 in. Because of this, it is unusual see needs a solidverotor If yourto car nted thicker rotors , than 112 in. refer to the rotor section in Chapter 3. If yourtypes car of needs vented rotors, Various vented rotors are 3. refer to theYour rotorbrake section in Chapter available. supplier will be Various types of rotors are able to compare thevented merits of one type available. Your brake be versus another. I supplier suggest will using able to compare thecurved merits vents of oneiftype vented rotors with you versus another. I suggest using can afford them. The cooling advanvented rotors with curved vents if you tages are worth the expense.

can afford them. The cooling advantages are worth expense. CALIPER SELthe ECTION Caliper

and

rotor

selection

go

CALIPER SELECTION together because they often come

Caliper and manufacturer. rotor selection go from the same He will together they works often with comea supply a because caliper that from the same manufacturer. will certain-diameter and -thicknessHerotor. supply a caliper that works with Make sure the caliper fits in thea certain-diameter andcalipers -thickness desired area. Some are rotor. more Make caliper fits in the compactsure thanthe others. Pay attention to desired area. You Somemust calipers more the details. not are machine compact others. Pay attention to metal off than a caliper to provide clearance the details. You must not machine to a wheel or suspension member. metal offuse a caliper to provide clearance Also, a caliper that will mount to a wheel suspension member. on your or suspension or chassis Also, use aSome calipercalipers that will components. aremount easily on your suspension or adapted to existing components.chassis Concomponents. calipers are sult a brake Some manufacturer. He easily may adapted to existing components. Conoffer a ready-made caliper mounting sult a brake manufacturer. He may bracket. offer a ready-made caliper mounting If you are also designing a new bracket. suspension, be sure to consider the If you and are also designing new caliper provide space a large suspension, be sure to consider enough for it. A proper caliperthe is caliper bit and asprovide spaceas large every important the enough for it. A proper caliper is suspension. every bit as suspension.

important

as

the

Don ' t buy a caliper that must use a flimsy mounting bracket. Make sure buy isa caliper thatand muststrong. use a theDon't bracket very stiff flimsy Extra "mounting beeP ' on bracket. this partMake helps sure the the bracket very stiffbracket and strong. braking. A ismounting that Extra "beef' onpoor this brake part helps the twists can cause performbraking. A mounting ance and uneven pad wear.bracket that twists cause poor delivered brake performThe can brake torque by a ance and uneven pad wear. caliper and rotor must be as great or The than brakewhat torque delivered by a greater is required for maxicaliper and rotor mustThe be as great or mum deceleration. maximum greater what is required for by maxipossiblethan brake torque is limited the mum deceleration. The maximum maximum operating pressure the calipossible torqueIfisthis limited by the per can brake withstand. maximum maximum the calipressure isoperating exceeded,pressure the caliper can per can withstand.theIf this flex excessively, seals maximum can leak pressure is exceeded, the caliper caliper can can and, in severe cases, the flex excessively, the seals can leak fail. Never design a brake system that and, in severe cases, the caliper can exceeds the manufacturer's recomfail. Never design a brake system mended maximum-pressure rating.that exceeds theRotor manufacturer's recomCaliper & Placement-When mended maximum-pressure rating. fitting brakes to a new car, it's imporRotor tant to position theP1aeement-when caliper in the best fitting to a the new rotor, car, it'sand imporpositionbrakes around the tant toand position theincaliper in the best rotor caliper the best lateral position around the rotor, and the position. rotor and caliper in the bestposition lateral First, let's consider caliper position. aro und the rotor. Assume you are First, let's consider caliper position looking at the left-front wheel from around the rotor. Assume you are the outside. Theoretically, the caliper lookinggoat at the any left-front wheel from1 could position from the outside. o'clock to 12Theoretically, o'clock. Therethe arecaliper many could go at any position things to consider, such as from existing1 o'clock to 12 o'clock.bleeding, There arespindle many mounting bosses, things to consider, such as and existing deflection, air-duct location, susmounting pension andbosses, steeringbleeding, clearances.spindle deflection, air-duct location, susIf you have an existing car,and mountpension and steering clearances. ing bosses on the spindles- or If you have uprightsmay an existing dictate car, mountcaliper ing bosses on isthebestspindles-or at 3 and 9 location. Bleeding uprights-may dictate positioned caliper o'clock. Usually, calipers location. Bleeding is best at 3 and 9 at 12 and 6 o'clock must be removed, o'clock. Usually, positioned rotated and have acalipers spacer inserted to 12 .and 6 o'clock be removed, at bleed Spindle and must axle-shaft deflecrotated and have a spacer can inserted to cornering cause tion during bleed. Spindle and axle-shaft defleccaliper-piston knockback with calipers tiontheduring cause 12- andcornering 6-0'clock can positions. at caliper-piston ktiockback with calipers This should not be a problem with at the 12- hubs and or 6-o'clock positions. full-floating sliding calipers. This shouldairnot be aenter problem Because ducts from with the full-floating hubs or sliding calipers. front of a brake, 3 o'clock is usually Because from can the best for theaircaliducts per soenter the ducts 3 o'clock is usually front of a brake, enter the center of the rotor at 9 best for the caliper suspension so the ductsclearcan o'clock. Although enter differ the center of tothecar,rotor ances from car thereatare9 o'clock. Although suspension usually ball joints and uprights clearat 12 ances differ from car to car, arms there are are and 6 o'clock. Steering usually ball joints and uprights at 12 either at 3 or 9 o'clock . Usually, when and 6 o'clock. Steering everything is considered , 3 arms o'clockare is either at 39 or 9 o'clock. Usually, when best and o'clock is second best, but everything considered, is any positionis will work. It 3allo'clock depends best and 9 o'clock is second best, but on what is best for your car. anyFor position work. It all lateral will positioning, thedepends things

on what is best for your car. For lateral positioning, the things

Caliper did not fit wheel correctly, so metal was removed from outboard edge. Don't do this to get a caliper to fit. Caliperso flexing, Caliper did not fit wheel correctly, metal cracking or other problems edge. may Don't result do if was removed from outboard excess metal is removed. Instead, flexing, select this to get a caliper to fit. Caliper calipers and wheels that clear without cracking or other problems may result if modification. excess metal is removed. Instead, select

calipers and wheels that clear without

to consider are eXistIng mounting bosses, and wheel and suspension to considerWith are anexisting clearances. existingmounting car, you bosses, and wheel and suspension may be able to use existing bosses and clearances. Withbut an you existing car, you hole locations, will probably may be able to use existing bosses have to fabric ate an adapter plate.and It hole but I/2-in. you will probably must locations, be rigid . I like steel plate. have to fabricate an adapter It Position each caliper so itplate. has at like 112-in.tosteel must be rigid. I clearance the plate. wheel least O.080-in. it has at Position and 114 in.each to caliper moving sosuspension least 0.080-in. clearance to the parts. Be sure to check the fron wheel t susand 114with in. the to steering moving atsuspension pension full lock, parts. and Be sure to check front posisusleft-turn. If nothe caliper rightpension with the steering at full lock, tion can be found that clears at full rightand left-turn. If nostops. caliperExcept posi'steering lock, consider tiondirt canoval-track be found cars, that few clears at cars full for race lock, as consider 'steeringangle stops.as Except need much steering a road for dirt oval-track cars, few race cars car. need much steering anglecaliper as a road RotorasOffset-Once lateral pocar. sition is found, the rotor position is Rotor Offset-Once caliper pofixed. Determine lateral rotor-hat offset sition is found, the rotor position is next. Hat offset is the distance from fixed. Determine rotor-hat offset the hub mounting surface to the rotor next. Hat offset the distance mounting surface.is Never order from hats the hubthe mounting the rotor until calipersurface and torotor are mounting order hats positioned. surface. Rotor Never hats with almost untiloffset the cancaliper and off rotor are any be supplied the shelf positioned. hats with byalmost or machinedRotor to specification your any offset canorbe supplied off the shelf brake dealer manufacturer. or machined to specification your, Rotor-Hat Holes-For some by reason brake dealer or manufacturer. many hats come with large holes Rotor-Hat Holes-For some reason, around their circumference. These many hats come with large holes holes help air flow to the outboard suraround These solid circumference. rotors and ventilated face of their holes help air flow to theairoutboard surrotors not using sealed ducts. With face ofducts solid rotors and ventilated sealed , these holes allow cooling

rotors not using sealed air ducts. With sealed ducts, these holes allow cooling 97

Sprint-car rear axle: Single inboard brake on solid axle is possible because of exposed axle rear shaftaxle: and Single locked inboard rear end. Not Sprint-car brake only is weight by because one-half,ofwhen on solid axle isreduced possible exone wheel a bump, brake rear moves smalposed axlehits shaft and locked end. Not ler distance than wheel,byreducing brake's only is weight reduced one-half, when effective weight. Improved hanone wheelunsprung hits a bump, brake moves srnaldling results. than Photowheel, by Tomreducing Monroe. brake's ler distance -

Inboard rear brakes are used on this Formula Ford. Brake COOling is excellent, rotor diameter is not limited by wheel size, and handling on rough surfaces is improved . Inboard brakes are not rear usedbrakes on ground-effects cars because they reduce tunnel width and resulting lnboard are used on this Formula Ford. Brake cooling is excellent, rotor diamedownforce. ter is not limited by wheel size, and handling on rough surfaces is improved. lnboard brakes

-

effective unsprung weight. Improved handling results. Photo by Tom Monroe.

are not used on ground-effects cars because they reduce tunnel width and resulting downforce.

Caliper mounts to quick-change side-bell and rotor-to-axle adaptor clamps to axle shaft: Actual sprint-car installation is at right. Note bearing housing- cage-with control-arm brackets at outer end axle. Photo at left courtesy AP Racing; photo at right courtesy Tilton.

Caliper mounts to quick-change side-bell and rotor-to-axle adaptor clamps to axle shaft: Actual sprint-car installation is at right. Note bearing housing-cage-with control-arm brackets at outer axle.allow Photo at left courtesy photo at right Tilton. of the air to escape from the center only doesend this larger rotors, AP Racing; such as those forcourtesy an independently

rotor before it flows through the

air to escape from the center the rotor. Consequently, these ofholes rotor before it flows through the should be plugged. When ordering rotor. Consequently, holes new hats, specify with these or without should depending be plugged. ordering holes, on When your rotor and new hats, specify with or without cooling system. If existing hats have holes, and depending rotor aluand you wishon to your plug them, holes cooling If existing hats have minum system. tape with high-temperature holes andworks you wish adhesive well.to plug them, aluminum tape with high-temperature Inboard Brakes-For one reason or adhesive works well. want to consider another, you might Inboard Brakes-For reasonNot or mounting the brakes one inboard. another, you might want to consider mounting the brakes inboard. Not

98

cooling is better because the brakes only not doesshrouded this allowby larger rotors, are the wheels. cooling is better because the Wheel-weight reduction alsobrakes imare not handling shroudedon byrough the surfaces wheels. proves Wheel-weight and brake torquereduction does not goalso into imthe proves handling on rough surfaces suspension. and brake torque doesbrakes not gomounted into the Why aren't many suspension. inboard? To begin with, they compliWhya aren't many . brakes mounted For example, cate car design inboard? To begin with, they mounting provisions must becomplimade cate a car For example, for the rotordesign. and caliper on the mounting provisions mustand be joints made, chassis. Then an axle shaft

for the rotor and caliper on the chassis. Then an axle shaft and joints,

sprung, driven wheel, must be used. such as the those for must an independently spindle rotate in the Finally, sprung, driven wheel, must be used. upright. All this increases complexity, Finally, the spindle must rotate the cost and weight. To top it off, inmost upright. All this increases complexity, front-wheel-drive cars don't have cost top it Race off, most roomand for weight. inboardTobrakes. cars front-wheel-drive cars don't have using ground effects need the narrowroombody for possible inboard brakes. cars between Race the side est using ground thethe narrowducts; inboardeffects brakesneed make body est the side andpossible reduce between the aerodynamic widerbody ducts; inboard brakes make the body downforce on the car. Use inboard wider and reduce the aerodynamic brakes if it makes sense , but keep in

downforce on the car. Use inboard brakes if it makes sense, but keep in

TOTAL PISTON AREA FOR EACH TYPE OF CALIPER AT = Total Piston TOTAL PISTON AREA FOR EACH TYPE OF CALIPER

Type of Caliper

Area (sq in.)

Fixed mount-one piston on each side of rotor Type of Caliper Fixed mount-two pistons on each side of rotor Fixed mount-one piston on on each side of rotor Fixed mount-three pistons each side of rotor Fixed mount-two pistons rotor Floating mount-one pistonononeach onlyside one of side of rotor Fixed mount-three of rotor Floating mount-twopistons pistonson oneach only side one side of rotor Floating mount-three mount-one piston on on only oneone side of rotor Floating pistons only side of rotor Floating pistons on only one side of rotor Ap = areamount-two of one piston (sq in.)

A, =Total Piston Area (sq in.) 2AP

4AP 6AP 2AP

4AP

Floating mount-three pistons on only one side of rotor GAP A, = area of one piston (sq in.) Chart gives total piston area for each type of caliper. Floating-sliding-caliper

has one piston doing job of two in a fixed caliper. If you don't know the type of caliper, remember that calipers piston(s) one Floating-sliding-caliper side. Area Ap of each piston in Chartfloating-mount gives total piston areahave for each typeon of only caliper. has is one square doing inches. Determine for your particular piston job of two inAp a fixed caliper. If youcaliper. don't know the type of caliper, remember

that floating-mount calipers have piston(s) on only one side. Area A, of each piston is in square inches. Determine Ap for your particular caliper.

mind the concept.

disadvantages

of

the

mind the disadvantages of the concept. DETERMINE HYDRAULIC-SYSTEM DETERMINEPRESSURE OPERATING HY DRAULIC-SY T E M torque is Once required Sbrake OPERATING PRESSURE known and you've made a caliper Once required braketo determine torque is selection, it's possible known and you've made caliper fluid pressure. Some brake a catalogs selection, it's possible to determine give the relationship between hydraufluid pressure. catalogs andSome brakebrake torque for a lic pressure give thecaliper relationship betweenHowever, hydraugiven and rotor. lic pressure and for a remember that brake the torque torque-vergiven caliper and rotor. However, sus-pressure relationship depends on remember that coefficient. the torque-verbrake-lining friction sus-pressure depends on fluid pressure required To find therelationship brake-lining friction coefficient. for your car, you need the following To find the fluid pressure required information: for your car, you needcoefficient. the following • Brake-lining friction information: • Total piston area for each caliper. Brake-lining friction coefficient. effective radius. • Rotor Total piston area for each caliper. • Brake torque at maximum decelerRotor effective radius. ation. Brake at maximum decelerIf you torque have the friction coefficient ation. for your linings, use it. Otherwise, If you it's have friction coefficient assume 0.3.the Most linings are this for your linings, it. by Otherwise, approximate value.use Start calculatassume it's 0.3. Most ing caliper-piston area: linings are this approximate value. Start by calculatArea of piston = 0.785 Dp2 in square ing caliper-piston area: inches Area piston = in square Dp = of Diameter of0.785 pistonDP2 in inches inches Total piston area is the area of one D p = Diameter of piston in inches piston multiplied by the number of Total piston area is the area of one pistons for a fixed-mount caliper. If pistonhave multiplied by caliper, the number of you a floating multiply pistons fixed-mount If the areafor of aone piston by caliper. twice the you have a floating caliper, multiply total number of pistons to get total efthe area of one mice the fective piston area.piston This by is illustrated total number of pistons to get total efabove. fective piston selected area. Thisa iscaliper illustrated If you've with above. non-circular pistons, such as those If you've selected a you caliper from Alston Industries, mustwith use non-circular pistons, as those an effective piston area insuch the formulas. from Alston Industries, must use piston area foryou each caliper Effective eJfective piston area in the formulas. an is given in the caliper manufacturer's Effective piston area for each caliper is given in the caliper manufacturer's

catalog. If you use a formula that requires using piston diameter, you catalog. If you use formula that remust compu te a effective piston quires diameter.using This piston is the diameter' diameter of a that has an area piston equal circular must piston compute effective diameter. Thisarea is the diameter of a to the piston of the non-circular circular piston that has an area equal caliper. All formulas requiring piston to the piston area using of thethis non-circular diameter will work method. caliper. formulas requiring piston Brake All effective radius is the distance diameter will work using this method. from the center of the rotor to the Brakeofeffective radiuspad. is the distance center the brake Once you from center ofradius, the rotor to folthe know the the effective use the center of the brake pad. Once you to compute fluid preslowing formula knowatthe effectivebrake radius, use the folsure maximum torque.

lowing formula to compute fluid presT sure at maximum torque. hydraulicbrake pressure = __ 8_ Maximum ,uLATrE

in pounds hydraulic per squarepressure inch Maximum

'8 =-

T 8 = Brake torque in inch-pounds PLAT'E in Dounds Der sauare inch of brake ,uL = Coefficient-of-friction T,' = rake torque in inch-pounds linings p Coefficient-of-friction of brake AT, == Total area of caliper pistons in linings inches square A, Total arearadius of caliper pistons in r E == Effective of brake in inches

square inches r, = Effective radius of brake in inches

Once maximum pressure is calculated, make sure the caliper can Once at maximum is operate this pressure .pressure Usually, the calculated, make sure the caliper can maximum operati;lg-pressure rating operate at thisis pressure. the of the caliper specified Usually, by the brake maximum operatiag-pressure manufacturer. It varies from rating about of the tocaliper specified by theonbrake 1000 1500 ispsi, depending the manufacturer. It varies caliper. The caliper cannot from safely about oper1000continuously to 1500 psi, above depending on the ate maximumcaliper. The caliper cannot safely operrated pressure because seal or caliperate continuously above maximumbridge fatigue failure may occur. rated pressure because seal or caliperHowever, an occasional locked-wheel bridgestop fatigue panic is OK. failure may occur. However, an occasional locked-wheel If calculated fluid pressure is too panic stop is OK. high for the caliper, the solution is If calculated fluiddopressure simple. You can one ofis too the high for the caliper, the solution is following: simple. can with do more one ofpiston the • Use a You caliper following: area - bigger pistons or more of them. a caliper withcaliper more onpiston • Use Use more than one each arearotor. bigger pistons or more of them. Use more than one on each • Use a larger rotorcaliper diameter, if

rotor. Use a larger rotor diameter, if

{

\--.-/ Effective radius of disc brake is measured from center of pad to center of rotor. Make sure you have correct combiEffective radius of discrotor/caliper brake is measured nationcenter to determine effective radius. from of pad to center of rotor. Make

sure you have correct rotor/caliper combination to determine effective radius.

there's space. • Use a caliper that has a higher there's space. operating pressure. Use caliper that one has caliper a higher If youause more than per operating pressure. rotor, each caliper supplies its rated If you Thus, use more one caliper per torque. twothan calipers on each rotor, doubles each caliper suppliesthat its brake rated rotor the torque torque. Thus, calipers on fluid each can deliver. Fortwo a given torque, rotor doubles the torque that brake pressure for a two-caliper disc brake can be deliver. Forfor a given torque, will half that a single caliper;fluid repressure fluid for a displacement two-caliper disc quired willbrake be will be half that for a single caliper; redouble. quired fluid displacement will you be Operating Pressure-In general, double. should use an operating pressure Operating general, you that's wellPressure-In below maximum-rated should operating pressure use for aancaliper. Leaks pressure and exthat's well below can maximum-rated deflection result from cessive pressurefluid for apressure. caliper. Leaks and exexcess If maximum cessive deflection resulthalf from operating pressure can is, say, of excess fluid pressure. If maximum maximum-rated pressure for the operatingthepressure is, say, half of caliper, extra margin of safety in maximum-rated pressure for the the brake system is sufficient.

caliper, the extra margin of safety in the brake&system is sufficient. PEDAL LINKAGE DESIGN After selecting and positioning the

PEDAL & LINKAGE DESIGN brakes and calculating maximum After selecting and positioning the hydraulic-system operating pressure, brakes calculating maximum the next and step is to design the pedals hydraulic-system operating pressure, and linkage. Various types of pedals the next step is to design the are discussed in Chapter 6. As pedals stated and linkage. types of pedals earlier, use Various a hanging pedal if 6. As stated are discussed Chapter possible . This in allows the master cylinearlier, a hanging pedal ders to beuse mounted high in the car forif possible. This allows the master cylinon easy servicing. Also, brake balance ders to be mounted in tothe car for balance-bar setups ishigh easier adjust. easy servicing. Also, of brake balance on The disadvantage hanging pedals balance-bar setups is easier to adjust. is the extra height required. On a lowThe disadvantage hanging profile race car, thereofmay not bepedals suffiis the extra a lowcient roomheight for required. hangingOnpedals. profile race car, there not be Consequently, you'llmay have to suffiuse cient room for hanging pedals. floor-mounted pedals. Consequently, you'll have to use floor-mounted pedals. 99

Hurst! Airheart 200X2 caliper is largest one offered by this manufacturer. Brake torque is rated2 0at brake Hurst/Airheart 0 x 223,000 caliperin-Ib is largest torque at 1200-psi hydraulic pressure. one offered by this manufacturer. Brake Double-piston caliper is popularin-lb for use on torque is rated at 23,000 brake racing stock cars. Photo courtesy Hurst torque at 1200-psi hydraulic pressure. Performance. Double-piston caliper is popular for use on Two calipers on rotor doubles brake torque for a given hydrauliC pressure-an easy and effective means of lowering pedal effort or fluid pressure. Smaller single-piston caliper is stiffer than a dual-piston caliper, too. torque Photo by Monroe. .TWO callpars u r i rudor doubles brake TorTom a ylven nyaraullc pressure-an easy and ef-

fective means of lowering pedal effort or fluid pressure. Smaller single-piston caliper is stiffer than a dual-piston caliper, too. Photo by Tom Monroe.

Ideal race-car brake- pedal setup; balance bar with remote adjuster. Remote - adjuster cable is routed to left of balance bar under clutch pedal. Floor-mounted pedals are necessary Idealbecause r,-- .,- of -.low-profile ,., .-,,, body height. d ; balance bar with remote adjuster. -r

,.,

.,.,.

,,,,.

cable is routed to left of balance bar under clutch pedal. Floor-mounted pedals are necessary because of low-profile body height.

Decide at this point what type of brake-balance method to use . There this point whatfortype of areDecide severalatchoices available a race brake-balance method to use. There car: are• several available for a race Balancechoices bar. car:• Adjustable proportioning valve. Balance bar. of the two. • Combination Adjustable proportioning Road cars usually don't use valve. balance thedifficult two. to inbars Combination because theyofare Road cars usually don'tpedals. use balance corporate into existing Also , bars are difficult to inbrakebecause balance they for road use is not as corporate existing pedals. predictableinto as for ｾ ｡｣ｩｮｧＮ＠ This isAlso, bebrake road balance use istypes not as cause carsfor runroad on many of

predictable as for racing. This is because road cars run on many types of

100

surfaces. And, adjusting a balance bar while driving on the road is simply not surfaces. bar practical. And, On a adjusting race tracka, balance conditions while driving on the road is simply not are stable or reasonably predictable . practical. a race track, conditions Also, the On driver constantly uses the are stable reasonably brakes hardorand can sense predictable. the need to Also, the driver constantly uses the adjust balance. brakes hardbars and are can used senseon therace needcars to Balance adjust for twobalance. m ain reasons: are pedal used on carsa Provides bars stiffer fee race l than • Balance for two main reasons: proportioning valve . Provides master stiffer pedal feelare than cylinders easya • Separate proportioning to change to mvalve. ake large bra ke-balance

Separate master cylinders are easy to change to make large brake-balance

racing stock cars. Photo courtesy Hurst Performance.

changes. An adjustable proportioning valve has limited adjustment. changes. An adjustable If you plan on using aproportioning balance bar, valve has limited adiustment. consider using an adjustable proporIf youvalve, plan on a balance tioning toousing . A balance bar bar, can consider using an adjustable proporbe adjusted to accomplish the desired tioning valve, brake too. Abalance, balance but bar can front-to-rear the be adjusted to valve accomplish desired proportioning does itthe autom atifront-to-rear brake balance, but the cally over a limited range of tire-grip proportioning valve does it automativalues. The disadvantage of using a cally over a limited rangea balance of tire-grip proportioning valve with bar values. The disadvantage of using a is the added weight , cost, complexity proportioning valve with a balance bar and pedal travel. is Unless the added weight, cost, complexity you like climbing into a raceand pedal travel. car cockpit upside down on your back, Unless climbing make sureyou thelike balance bar into can aberaceadcar cockpit upside down on your back, justed from a convenient position. makemay sureaffect the balance bar canposition be adThis the mounting justed fromfora the convenient position. you choose pedals. But , pedal This may affect the mounting are position and balance-bar maintenance critiyou choose for the pedals. But, cal to keeping a. brake system inpedal top and balance-bar maintenance are critioperating condition. A balance bar cal a. brake system in and top withtoa keeping remote-adjustment cable operating condition. A balance bar knob may be the solution. with a remote-adjustment and Brake-pedal ratio and cable masterknob may be the solution. cylinder size (s) should be selected at theBrake-pedal same time.ratio The and objectmasteris to cylinder the size(s) shouldoperating be selected at achieve maximum presthe same time. The object is to sure you established with an acceptachieve the effort maximum presable pedal usingoperating the following sure you established with an acceptsteps: able pedal effort the following pedal ratiousing . • Select steps: • Select pedal effort at maximum Select pedal ratio. deceleration. pedal at maximum • Select Calculate forceseffort on master-cylinder deceleration. push rod (s) . Calculate forces on master-cylinder master-cylinder diameter(s) • Select pushrod (s) . that gives proper maximum operating Select in master-cylinder diameterk) pressure hydraulic system. that gives geometry proper maximum operating • Check of the pedal and pressure in hydraulic system. linkage at extremes of travel. of theandpedal and • Check Design geometry pedal bracket masterlinkage atmount. extremes of travel. cylinder

Design pedal bracket and mastercylinder mount.

MASTER-CYLINDER SIZE VS. PISTON AREA

Making under-dash brake-balance adjustment forces mechanic into this uncomfortable position. Hanging brake pedal with Making under-dash brake-balance adjustbalance bar and remote into adjuster more ment forces mechanic this is uncompractical.position. Hanging brake pedal with fortable balance bar and remote adjuster is more practical.

• Change anything necessary and start over. l Change anything necessary and Pedal Ratio- There is nothing Select start over. magic about the pedal ratio. Many Select Pedal Ratio-There is nothing values are possible. However, if you magic know aboutwhat the to pedal don't use, ratio. try a Many pedal values possible. However, if you of are about 5.0. ratio don't know try use a pedal If you buywhat a settoofuse, pedals, the ratio about 5.0.into them. Unless the pedalofratio built If you buy a set of pedals, use the resulting master-cylinder size(s) or pedal them. the linkage movement is incorrect, you resultinghave master-cylinder Size(S) or should a good design. Don't linkage amovement incorrect, you design new pedal isunless you have should a good design. Don't to. It is have time consuming and difficult design a new pedal unless you have to do correctly. to.Some It is time consuming and difficult points to consider when to do correctly. selecting a pedal ratio: Some a points • With given to pedalconsider ratio, iswhen the selecting a pedal ratio: master cylinder(s) mounted in a conl With place? a given pedal ratio, is the venient master cylinder(s) mounted in a conget master cylinder(s) with • Can you venient place? enough stroke so the pedal hits the l Can before you getthe master cylinder(s) with floor master cylinder(s) enough bottoms?stroke so the pedal hits the floor master cylinder(s) • Doesbefore the the pedal position feel bottoms? comfortable? D o e s the feel Pedal pedal Effort position at Maximum Selecting comfortable? Deceleration-Most people can stop a Selecting Pedal Effort Maximum car that requires 100-lbatpedal effort. Deceleration-Most stop for acan road car.a However, this is highpeople car that requires 100-lb pedal effort. And, it may not allow enough safety However,forthis is high road car. or margin brake fadefor fora street And, not allowthat enough racing.it Imay recommend you safety use a margin for brake street or 75-lb pedal effortfadeforformaximum racing. I recommend that you deceleration. If you use less use pedala 75-lb pedal effort for maximum effort, the brake pedal will feel less deceleration. If you less pedal moreuse travel. rigid and will have effort, the brake pedal will feel less Master-Cylinder Pushrod Force-If rigid and will have more travel. your car uses a tandem master cylinMaster-Cylinder Pushrod Force-If der or a single master cylinder, the your car tandem master cylinforce on uses the apushrod is found by

der or a single master cylinder, the force on the pushrod is found by

Nominal Diameter MASTER-CYLINDER SIZE VS. PISTON AREAArea Bore Size In. Sqln. Nominal Diameter Area 5/8 in. 0.6250 0.3068 Bore Sire In. Sq In. 11/16 in. 0.6875 0.3712 5/8 in. 0.6250 0.3068 19mm 0.7480 0.4394 11/18in. 0.6875 0.371 2 3/4in. 0.7500 0.4418 19mm 0.7480 0.4394 20mm 0.7874 0.4869 3/4 in.in. 0.7500 0.4418 13/16 0.8125 0.5185 20mm 0.7874 0.4869 21mm 0.8268 0.5369 13/16 in. 0.8125 D.5185 22mm 0.8661 0.5892 21 mm 0.8268 0.5369 22.2mm 0.8740 0.5999 22mm 0.8661 0.5892 7/8 in. 0.8750 0.6013 22.2mm 0.8740 0.5999 23mm 0.9055 0.6440 7/8 in.in. 0.8750 0.661 3 29/32 0.9063 0.6451 23mm 0.9055 0.6440 15/16in. 0.9375 0.6903 29/32 in. 0.9063 0.6451 24mm 0.9449 0.7012 0.9375 0.6903 15/16 In. 25.4mm 1.0000 0.7854 24mm 0.9449 0.701 2 1 in. 1.0000 0.7854 25.4mm 1,0090 8.7854 ＱｾＯＳＲ＠ in. 1.0313 0.8353 1 in. 1.OOOO 0.7854 26.6mm 1.0472 0.8613 1-1/32 in. in. 1.0313 0.8353 1-1/16 1.0625 0.8866 26.6mm 1.0472 0.861 3 1-1/8 in. 1.1250 0.9940 0.8866 1-1/16in. 1.0625 28.6mm 1.1260 0.9958 1-1/E3 in. 1.7250 0.9940 1-1/4in. 1.2500 1.2272 28.6mm 1.f26Q 0.9958 31.8mm 1.2520 1.2311 In. 1.2600 1.2272 1I-1/4 ｾＵＯＱＶ＠ in. 1.3125 1.3530 3?.8rnm 1.2520 1.231 I 1-11/32in. 1.3438 1.4183 1-5/16in. 1 3 125 1.3530 1-1/2in. 1.5000 1.7671 1-1 1/32 1.3438 1,4183 1-3/4 in. in. 1.7500 2.4053 1-1/2 In. 1.5000 1,7671 1.7500 2.4053 1-3/4 in. Listed are diameters of popular mass-produced master cylinders and their areas. Note that some metric sizes are close to standard inch sizes. Be careful to get correct sizes when buying replacement Many mass-produced cylinders have diameters marked and on them. Listed are diametersparts. of popular master cylinders their areas. Note that some metric sizes are close to standard inch sizes. Be careful to get correct sizes when buying replacement parts. Many cylinders have diameters marked on them.

multiplying the pedal ratio by pedal effort. multiplying the if pedal For example, pedalratio ratiobyis peda! 10.0 effort. and pedal effort is 75 Ib, force on the For example, pushrod if pedal isratio is 10.0 master-cylinder 750 lb. and pedal effort is 75 Ib, force on the the If you are using a balance bar, master-cylinder pushrod is 750 lb. force just calculated above is the pedal If you a balance bar, Itthe thatare actsusing on the balance bar. is force force justbetween calculated is the cylinpedal divided the above two master force that acts ontothethe balance bar. Iton is ders according formulas divided between the two master cylinpage 75. ders according to on I recommend thatthe youformulas assume the page 75. bar divides pedal force equally balance I recommend thatmaster you assume the between the two cylinders. balance bar divides pedal force equally This allows the maximum amount of between the adjustment two master incylinders. balance-bar either This allowsItthe maximum amount of direction. also makes the design balance-bar adjustment in either easier. If you do this, divide equally direction. It pushrod also makes design the resulting forcethe found by easier. If you do effort this, divide equally multiplying pedal by pedal ratio. the resulting by This gives thepushrod force onforce eachfound mastermultiplying pedal effort by pedal ratio. cylinder pushrod. If you do not center This gives the on each masterthe balance bar,force calculate the force to cylinder pushrod. If you do not center each pushrod. theNow balance the on force to that bar, you calculate have force each each pushrod. pushrod, you also have the force apNowto that have force onpiston. each plied eachyou master-cylinder pushrod, you also have the force apThe forces are the same.

plied to each master-cylinder piston. The forces are the same.

Master-Cylinder Size-Now that you know the desired maximum Master-Cylinder Size-Now operating pressure and force on that the you know the desired master-cylinder piston, it's maximum simple to operating the pressure and force on the the required area for calculate master-cylinder piston, it's simple to master-cylinder piston:

calculate the required area for the F master-cylinder piston: Master-cylinder-piston area

=

ｾ＠

p square inches in ~aster-cylinder-piston area - F M C FMC = Force on master-cylinder P piston insquare in pounds inches FMc Force onpressure master-cylinder piston P = = Hydraulic in pounds per square inch in Pounds = Hydraulic pressure in pounds per

inch

A list of piston areas for commonly available master-cylinder diameters is A listinof piston areas for commonly given the accompanying table. available master-cylinder diameters is Most cars use 3/4-1-in.-diameter given the accompanying table. master in cylinders. If your calculated Most cars use 314-1-in.-diameter area falls between two standard sizes, master the cylinders. If your calculated choose master-cylinder diameter area falls between two closest to the required standard area. Yousizes, can choose the adjustments master-cylinder make small later diameter with the closest balance to bar.the required area. You can make small adjustments later witharea the If the required master-cylinder balance bar. is smaller than what's available, go to the required master-cylinder numerical pedal ratio area or a Iflarger

is smaller than what's available, go to a larger numerical pedal ratio 101 or

Pedal

1

.-

Pedal

Centerline

F-;r;

/J Must Be Less Than 5° For All Positions Pedal 0 Must BeofLess

Than 5" For All Positions of Pedal

L

Pushrod Make a drawing to determine angle between pushrod and mastercylinder centerline. Angle must not be excessive, or binding and rapid wear will result.angle Limit between angle to 5° maximum. If angle Makecylinder a drawing to determine pushrod and masteris too large, increase length pushrod or shorten total pedal cylinder centerline. Angle mustofnot be excessive, or binding and travel.cylinder Angle should be result. nearly Limit zero angle with pedal in positionIfwhere angle rapid wear will to 5" maximum. maximum deceleration Onpushrod most cars hanging is too large, increase occurs. length of or with shorten totalpedals, pedal this occurs with pedalbe at nearly about 2zero in. from travel. Angle should withfloor. pedal in position where

I

Floor-mounted Neal pedal bracket ties master cylinder to pedal pivot in one assembly. Only forces on chassis are those delivered directly by driver's on master cylinder and Floor-mounted Neal foot. pedalLarger bracketforces ties master cylinder to pedal pedal pivot taken byOnly bracket. pivot in oneare assembly. forces on chassis are those delivered

directly by driver's foot. Larger forces on master cylinder and pedal pivot are taken by bracket.

maximum deceleration occurs. On most cars with hanging pedals, power brakes However, this occurs with .pedal at about 2don't in. fromuse floor. the pedals and seat. Position them as

power brakes on a race car unless abpower brakes. However, use solutely necessary. There don't are easier power brakes on a race car unless abways of avoiding this, unless your solutely race car isnecessary. extremely There heavy. are easier ways of avoiding unless your If you select a this, 5/8-in.-diameter race car is extremely heavy. master cylinder, be aware that you If you goselect cannot to a a 5/8-in.-diameter smaller size master cylinder, be aware that Ityou later-there are none available. is cannot go a to a orsmaller size better to use 3/4-in. larger cylinlater-there It is der so you are can none makeavailable. a change, if better to use a 314-in. or larger cylinneeded. For example, if new tires give der youthan canwhat make change,for,if moresogrip youa allowed needed. For example, if new give you'll need smaller master tires cylinders more grip than what you allowed for, to keep the same pedal effort for maxiyou'll need smaller master cylinders mum deceleration. So, leave yourself to keeproom the same pedalchanges. effort forTo maxisome to make inmum deceleration. So, leave yourself crease the master-cylinder diameter some room topedal make changes. inand maintain effort, use aTo larger crease the master-cylinder diameter pedal ratio. and maintain pedal effort, use a larger Pedal & Linkage Geometry-A pedal ratio. brake pedal must be designed to fit Pedal & As Linkage Geometry-A the driver. the driver pushes the brake pedal must be designed fit pedal, the ball of his foot shouldtostay the driver. As the driver pushes the in contact with the pedal pad. Measure pedal,foot the orball his foot should stay your theofdriver's-if the sizes in contact with the pedal pad. Measure are significantly different-and check your or the driver's-if the sizes pedal foot positions. areAlso, significantly check look for different-and a car with pedals in pedal positions. the "perfect" position for the driver's Also, look forthe a carrelationship with pedalsbein feet. Measure the "perfect" position driver's tween the floor, ped als for and[he seat. Copy feet. Measure bethe design of a the goodrelationship car if you find tween the floor, pedals and seat. Copy one that's suitable. There is no perfect if you find the of abecause good car pedaldesign design, each person's one suitable. There is nodifferent perfect bodythat's has slightly pedal design,So, because person's dimensions. designeach yourdifferent car to body has slightly suit the driver. dimensions. SO,doubts design about your car to If you have pedal suit the driver. position, make a full-size model of

If you have doubts about pedal position, make a full-size model of 102

they will be in the car and see how the and seat. as theypedals fit. Now's the Position time to them change they will be in the car and see how things that are not comfortable. they fit.theNow's thethetime to change Check pedal in extreme posithings comfortable. tions of that travel.areYounot should have no Check the pedal in the more than 6 in. of totalextreme travel atposithe tions pad. of travel. You should have no pedal Try it to be sure. of total travel of at the more than After you6 in. make a drawing the pedal pad. it to be sure. and Try its mounts, check the linkyouextreme make apositions. drawing of the ageAfter at the There pedal and the linkshould be its no mounts, binding.check Pay particular age at thetoextreme positions. There attention the angle the pushrod should be no binding. Pay particular makes with the master cylinder. If the attention to the angleextreme the pushrod pushrod goes through angles makes m ~ master s t e cylinder. r cylinder, If the to the with bore the of the it extreme severe angles pushrod goes This causes can bind. the bore of the t-naster cylinder, Ait problems, including breakage. longer bind. pushrod may causes be required to Can This severe reduce the misalignment angle. A problems, breakage. longer pushrod may be required maximum of 5° misalignment between pushrod the and master cylinder angle. is recomreduce misalignment A mended See maximumby brake manufacturers. between pushrod and master Vlinder recornthe accompanying drawing forisan illusmended manufacturers. See tration ofby thisbrake pro blem. for an the Pedal-Bracket &drawing Master-Cylinder Mount-On many cars the pedal Uation this problem. Master-C~linder bracket and master-cylinder mount Mount-On many cars the pedal are the same. This makes a strong, b r x k system e t and with master-cylinder mount rigid minimum of overall are the Race-car same. This a strong, weight. pedalmakes brackets manurigid system with minimum of overall factured by companies such as Tilton, weight. brackets manuNeal or Race-car Winters pedal use this concept. A factured by colnpanies as Tilton, pedal bracket is difficultsuch to design, so Neal Winters use this concept. A buyingor one of these sturdy, lightpedal bracket is difficult to design, So weight brackets makes sense. These of these sturdy,applicalightparts areone designed for racing weight tions andbrackets are easy makes to use. sense. These are designed for racing applicaparts pedal-bracket design in I discuss tions and are easy to use. Chapter 6. However, re member this

I discuss pedal-bracket design i n 6 . However, remember this

important point: The bracket must not deflect an excessive amount when important point: The hard. bracket must the pedal is pushed A pedal not deflect an excessive amount when bracket mounted in the center of a the is pushed thin pedal sheet-metal fire hard. wall A ispedal 1101 bracket mounted center pedal of a satisfactory. This, in or the a flexible tfor thin sheet-metal fire airwall is hybracket, is worse than in the satisfactory. This, or a flexible pedal draulic system. With a flexible pedal bracket, worse than pump air in the bracket, isyou cannot up hythe draulic With a flexible pedal orsystem. bleed the trapped air to pedal cure bracket, you cannot pump up the the problem' pedal or bleed the trapped air cure I f you stress-analyze the to pedal the problem! bracket, remember to use maximum If you normal stress-analyze load-not operatingthe load.pedal The bracket, remember to use maximum maximum load occurs during a panic load-not operating stop when normal the driver pushesload. withThe all maximum loadIf occurs duringis astrong panic of his might. the bracket stop when driver pushes withfine all enough forthethis, it will work of his might. If the bracket is strong during maximum deceleration. enough Design for this,Problem-Following it will work fine Sample during maximum deceleration. is a sample race -car brake-design Sample Problem-Following problem. Design The steps are in the same is a sample race-car brake-design order presented . problem. The steps are in thesystem same First select the disc- brake ordergives presented. that the requi red brake torque at select the disc-brake a First 500-psi operating pressure system at the that gives the required brake at front brakes and 400-psi at torque the rear. a 500-psi operating are pressure at the These calculations explained in front brakes the first part ofand this400-psi chapter.at the rear. These calculations explained in system has an A proven pedal are the first part of this 8.0-to-l pedal ratio.chapter. I wish to design proven pedal has an forAa pedal effort of 75system lb at maximum 8.0-to-1 pedal ratio. I wish to deceleration. The pedal force design acting for the a pedal effort lb at maximum on balance barofis 75 calculated:

deceleration. The pedal force acting Force balance = PE Rp in on the on balance barbar is calculated: pounds PE = Pedal pounds on effort inbar = R~ i n pounds Rp = Pedal ratio effortinbarpounds pE = Pedal = (75 Ib)(8.0) Force on balance R, = Pedal ratio bar = 600 lb. Force on balance

',

Force on balance bar Force on balance bar

= (75 lb)(8.0) = 6 0 0 Ib.

Accident waiting to happen: Steel brake line must be secured to frame with a bracket where the flexible hose attaches (arrow). With this waiting setup, steel line is subjected to line bending fatigue as Accident to happen: Steel brake must and be secured to the suspension moveswhere up and the line will frame with a bracket the down. flexibleEventually, hose attaches (arrow). fracture, brakeline failure. With this causing setup, steel is subjected to bending and fatigue as the suspension moves up and down. Eventually, the line will fracture, causing brake failure.

Brake-line mounting bracket is simple plate, located near suspension pivots (arrow). This minimizes hose bending and pulling as wheel moves. Line and hose attaches bracket using an suspenaircraft Brake-line mounting bracket is simple to plate, located near bulkhead fitting. Jam This nut clamps bulkhead to bracket. sion pivots (arrow). minimizes hose fitting bending and pulling as wheel moves. Line and hose attaches to bracket using an aircraft bulkhead fitting. Jam nut clamps bulkhead fitting to bracket.

Assuming the balance bar divides pedal force equally between the front Assuming the balance cylinders,barthedivides force and rear master pedal force equally between the front lb. on each pushrod is 300 andAlthough rear master cylinders, the force the master cylinders have on eachforces, pushrod is 300 lb. equal different size cylinders cylinders have rear brakes. areAlthough required the for master front and equal forces, different size cylinders This is due to the difference in the are requiredpressure for frontofand brakes. operating therear front and This is due to the difference in the rear systems. operating of page the front From thepressure formula on 101: and

rear systems. F ｾ＠ Piston Fromarea the =formula on page 101: P F M ~ FMC = Force master-cylinder piston Piston area =on P in pounds Force onpressure master-cylinder piston FMc P= = Hydraulic in pounds per in pounds square inches P = Hydraulic pressure in pounds per For theinches front brakes, master-cylinder square piston area is:

For brakes, master-cylinder . the front 300lb Piston area = 500 psi oiston area is: 300 Ib = 0.6 sq in. Piston area =

For the rear-brake master cylinder: = 0.6 sq in. .

300lb

Piston = 400 psi For thearea rear-brake master cylinder: = 0.75 sq in. 300 Ib Piston area =400 psi The closest standard-size master = 0.75 sq in.

cylinder is selected from the table on The101:closest standard-size master page

cylinder is selected from the table on : page 101 master-cylinder diameter = 7/8 Front in. (area = 0.601 sq in.) Frontmaster-cylinder master-cylinder diameter diameter == 7/8 Rear in.in.(area sqsqin.) 1 (area==0.601 0.785 in.). Rear master-cylinder diameter = 1 in. (area = 0.785 sq in.). Note that the front master cylinder

is almost perfect and the rear cylinder that large. the front master is Note a bit too I'll use the cylinder balance is perfect and the the rearsystem. cylinder baralmost in testing to fine-tune is Also a bit note too large. the balance that I'll the use smaller master

bar in testing to fine-tune the system. Also note that the smaller master

Custom-fabricated reservoirs are secured with hose clamps and rubber cushions in between. Reservoirs will slipare if secured clamps CUJLUIII-~dbricated reservoirs loosens. with hose clamps and rubber cushions in between. Reservoirs will slip if clamps cylinder is considerably larger than loosens.

Reduced diameters at centers positively locate fluid reservoirs in mounting clamps. Clamps have toatloosen considerably R e u u ~ awould uularnerers centers poslr~vely before reservoirs could in slip. locate fluid reservoirs mounting clamps. Clamps would have to loosen considerably to complete a could brake-system design. before reservoirs slip.

the minimum size. This is good in cylinder is considerably wrong at thelarger start ofthan the case I guessed the minimum size. This is good in design. I can easily change hydraulicwrong the startsmaller of the case I guessed system pressure byat using easilya change hydraulicdesign. I can cylinders. When problem occurs, system by using smaller cylinder is reusually a pressure smaller master cylinders. When a problem quired to reduce pedal effort. occurs, usually smaller master cylinder is re-I After a finishing the calculations, quireda side to reduce draw view pedal of theeffort. pedals to check After geometry. finishing the calculations, linkage Because I selectedI draw a side view of the pedals checka from a standard pedal design to I selected linkage geometry. Because manufacturer, this step is probably anot standard pedal sets design required. Pedal shouldfrom be de-a manufacturer, this step is probably signed to work without binding.

The major items remaining are: to complete brake-system • Route brakealines on chassis. design. The major items remaining are: • Attach flex hoses to chassis. Route brake lines on chassis. • Locate and mount remote masterAttachfluid flex reservoir hoses to chassis. cylinder (s) (if used). Locate and mount remote master• Locate proportioning valve (if cylinder fluid reservoir(s1 (if used). used) . Locate mounts proportioning valverotors (if • Design for calipers, used). and other brake hardware. Design mounts for calipers, rotors • Design cooling-duct system, if and other brake hardware. required. Design that cooling-duct bleeders aresystem, accessibleif • Confirm required. and mounted high. Confirmthethatcarbleeders are accessible After is completed, the and mounted high. brake system must be tested before After use, theChapter car is 10. completed, the serious

not required. Pedal sets should be designed to work BRAKE without binding. COMPLETE SYSTEM There are now other steps required

COMPLETE BRAKE SYSTEM There are now other steps required

brake system must be tested before serious use, Chapter 10.

103

78sting

10

...

Testing is required to get maximum performance n any car, but particularly race cars. This includes brake testing. George B.,..>tti and Tom Sneva discuss effects of changes to car between practice runs while tire engineer measures tire temperatures. Photo by Tom Monroe.

served brake while it George operates. BrakeAs any you car, now a great Testing is required to get maximum performance from butknow, particularly racedeal cars.of This includes testing. Bignotti and dynamometer testing done the brake-system design processmeasures is Tom Sneva discuss effects of changes to car between practice runs while tire engineer tire temperatures. Photo is by usually Tom Monroe.

Brake dynamometer, designed to run continuously, is driven by a 289-cu in. Ford V 8 through a gearbox. Power delivered to brake is equivalent to a sedan under a hard stop. Datsun drum brake is being tested. Brake dynamometer, designed to run continuously, is driven by a 289-cu in. Ford V8 through a gearbox. Power delivered to brake is equivalent to a sedan under a hard stop. Datsun drum brake is being tested.

based on assumptions. For this reason, a brake-test program is absolutely necessary. Often, when a new As car youisnow know,and a great of race designed built, deal testing the brake-system design process is is neglected in favor of getting the car based on assumptions. For this to its first race. This is false economy. reason, program absoTesting aatbrake-test a race takes a lotis longer lutely necessary. Often , when a new than at a planned private test session. race car is designed and built, testing I've seen many people use up a whole isracing neglected in favor of getting the car season to get a car working to its first race. This is false economy. properly when they could've sorted at in a race takes longe r Testing out the car one full day aoflot testing. than at a pl anned private test session. Brake testing falls into two I' ve seen many people use up a whole categories: laboratory testing and racing season to get a car working track testing. Laboratory testing inwhen they couldbrake ' ve sorted properly volves running a single on a out the car in one full day of testing. testing machine called a brake Brake testing falls on into two See photo the back dynamometer. andto categories: laboratory cover. This type of testingtesting is similar track Laboratory intestingtesting an . engine on testing an engine running a single brake on a volves dynamometer. Because a brake is out testing machine called a brake in the open, it can be studied and ob-

dynamometer. See photo on the back cover. This type of testing is similar to testing an engine on an engine dynamometer. Because a brake is out in the open, it can be studied and ob104

by the big brake manufacturers, but if you are so inclined you can make such a device for yourself. served it operates. BrakeMost while brake-testing time will be dynamometer testing is usually spent on the track. You take the done car to by the bigtest brake manufacturers but if a private track and test the ,brakes. you are so inclined can make such Measuring brake you performance and apushing device for yourself. them to the limit should be a Most brake-testing timethat will part of the test. Many tests canbe be spent on the track. You take the car to done very easily during track testing awould privateotherwise test track and test the brakes. be difficult or imMeasuring brake performance and possible during a race. Even a practice pushing them to the limit should be a session during a race weekend is not of the test. Many tests that can be part appropriate for testing. Other cars on done very easily during the track prevent you track fromtesting doing otherwise be difficult would what is needed for a good test. or impossible during a race. Even a pract ice during a race weekend is not session BRAKE-DYNAMOMETER appropriate TESTING for testing. Other cars on theBrake track manufacturers prevent you use from doing brake dywhat is needed for a good test. namometers for laboratory testing. A

single brake is mounted o n and driven

BRAKE-DYNAMOMETER TESTING Brake manufacturers use brake dynamometers for laboratory testing. A single brake is mounted on and driven

by the dynamometer. Instruments measure and record such things as DY Lne temperature, uy narnomeler. rpm, 1nsLrumenrs brake brake measure record such thingsand as pressure torque, and hydraulic brake temperature, rpm, brake stresses. The dynamometer is powtorque, and ered by anhydraulic engine or pressure electric motor. stresses. The dynamometer is powUsually, a large high-speed flywheel is ered used. by an engine or electric motor. Usually, a large high-speed is Dynamometer testing flywheel involves used. revving up the flywheel until there is testing ofinvolves a Dynamometer predetermined amount energy revvinginupit. the is Theflywheel driving until motorthere is disstored aconnected predetermined amount of energy and the brake is applied to storedthe in flywheel it. The driving motor is disto a predetermined slow connected and the brake applied of to rpm or to a dead stop. Theis amount slow theenergy flywheelinto the a predetermined stored flywheel is rpm or to a dead stop. The known. It is equivalent to a amount fraction of of stored energy in the flywheel is the kinetic energy stored in a moving known. It is equivalent to a fraction of car, or about one-third of the total the kinetic energy one stored in brake a moving front and energy for testing car, or about one-third of one-sixth for one rear brake. the total energy for testing one front brake and Dyno testing tests a brake's energyone-sixth for one rear brake. absorbing capaci ty for one or a series Dyno testing a brake's energyof complete or tests partial stops. The flyabsorbing capacity for one or a series wheel can be stopped slowly or of complete or partial The flyrapidly, depending on stops. how much hywheel be stopped slowly or pressure is applied to the draulic can rapidly, depending on how much hybrake. Sophisticated dynamometers draulic pressure is applied to the are computer controlled and can be brake. Sophisticated dynamometers programmed to duplicate brake are computerspeeds controlled and can be and decelerations applications, programmed to duplicate brake encountered in city traffic, a mountain applications, speeds anda race decelerations descent, or laps around track . encountered in city a mountain Another type of traffic, dynamometer apdescent, or laps around a race brake. plies constant power to thetrack. Another type of input dynamometer This steady-power can be atap-a plies constant power to brake. heats up, particular rpm. As the brakethe This steady-power can be its torque changes.input Torque can atbea particular the brake .heats up, measured rpm. with As instruments Friction its torque changes. Torque can be change with temperature at a constant measured instruments.with Friction rpm can with be determined this change with temperature at a constant setup. rpm can be Measuring-The determined withsecret this Temperature setup. of proper brake-dynamometer testing Temperature Measuring-The is the instrumentation. A good secret setup of proper testing will havebrake-dynamometer numerous temperatureis the instrumentation. A good setup measuring devices mounted in critical will have numerous temperaturelocations on the brake. Generally, measuring devices mounted for this.in critical thermocouples are used locations on the brake. Generally, is a joint of two A thermocouple thermocouples are used for this. wires with dissimilar metal. When the A thermocouple is a joint of two joint, or thermocouple junction, is wires with dissimilar metal. When the heated , it generates a small electrical joint, junction, is voltage.or Thisthermocouple tiny voltage can be measheated, it generates a small electrical ured and converted to indicate a voltage. temperature This tiny voltage be measwithcan a pyrometer. specific ured and converted to indicate If the thermocouple junction is in con-a specific a pyrometer.a the item towith be measured, tact withtemperature

If the thermocouple junction is in contact with the item to be measured, a

HOW MUCH HORSEPOWER GOES INTO THE BRAKES? HOW MUCHisHORSEPOWER Horsepower the rate at which GOES is INTO THE BRAKES? energy delivered. The heat energy

Horsepower = 0 .00268W ed M S We = weight of car in pounds Horsepower = 0.00268WCd,S decleration in g's d M = maximum W weight of of car pounds S, = = speed the in car in miles per Horsepower is brakes the rate at awhich d , = maximum decleration in g's hour. received by the during stop S = speed of the car in miles per energy delivered. The heat energy can be isexpressed as horsepower. hour. received by the a stop For example, if brakes a brakeduring is driven by Because the speed of a car canengine be expressed horsepower. an on a brakeasdynamometer, changes during a stop, power to the For example, if a brake brake is driventhe by Because speedDeceleration of a car power into the equals brakes also the changes. an engine on of a brake dynamometer, changes during a stop, to the power output the engine. In a car, during the power stop due to may change power intoenergy the brake brakes changes. and Deceleration the kineic of the equals moving the car this also changesalso in downforce, power output the engine. In a that car, may change duringtothethe stopbrakes. due to supplies the of power. However, changes power the kineic energy of the moving car changes downforce, and this also kinetic energy originally came from Obviously,inthe highest power is for a supplies changes to lots the ofbrakes. the engine.the power. However, that car with downfast, heavypower Obviously, theracing highest power is for a kinetic energy originally One horsepower equalscame 550 from ft-lb force and big tires. the energy engine. delivered each second, fast, heavy with lots of downof calculations Below arecarsample ft-lb force andexplain big racing One horsepower The total power intoequals all four550 brakes that may whytires. bra'k es are deof energy delivered Belowtheare during a stop is given each by thesecond. followsigned waysample they arecalculations for various The total power into all four brakes that explain why brakes are deing formula: typesmay of cars. during a stop i s given by the followslgned the way they are for various ing formula: types of cars. d M (g's) Power(HP) Ty,p eof Car We (lb) S (mph) 515 0.8 4000 60 Large sedan, street tires Type of Car W, (Ib) S (mph) d, (g's) Power(HP1 257 0.8 2000 Small sedan, street tires 60 51 5 4000 60 0.8 Large street tires tires 2573 1.2 Racingsedan, stock car, racing 200 60 0.8 257 Small sedan, tiresdownforce 2000 2680 200 2.5 Fast race car street with high 2573 4000 200 Racingrace stock tires 120 386 1000 1.2 Small carcar, withracing low downforce 2000 200 2.5 2680 Fast race car with high downforce 386 1000 120 1.2 Small race car with low downforce

remote temperature measurement is possible. remote temperature is Thermocouples canmeasurement be used on any possible. stationary brake part. To measure Thermocouples useda on any moving parts, suchcan as abe rotor, sliding stationary brake part. To measure contact or more-sophisticated instrumovingare parts, such. as a rotor, a sliding ments needed Often, rotor temcontact or more-sophisticated perature is measured with ainstrutherments are brought needed. Often, rotor temmocouple into contact with perature is measured with therthe rotor immediately after thea brake mocouple brought into contact with stops. theA rotor immediately after connected the brake hand-held pyrometer stops. to a thermocouple probe is a useful A hand-held pyrometer brakeconnected and tire device for measuring to a thermocouple probetrack. is a useful temperatures at a race When device for the measuring brake and they tire racers use term pyrometer, temperatures at a race track. When usually mean hand-held pyrometer or racers use the term pyrometer, they thermocouple. usually hand-held pyrometer or There mean are many interesting comthermocouple. parisons to make when dynamometer ThereHere are are many comtesting. someinteresting possible tests: parisons to make when dynamometer • Comparison of brake friction matetesting. some possible tests: rials forHere fadeareresistance , wear and Comparison of brake friction matetorque. rials for fade resistance, wear part and the most critical • Determining torque. of braking system when excessive Determining most critical part temperatures arethe reached. of braking system whentemperature excessive • Finding the maximum temperatures are reached. a brake can withstand without failure. the maximum temperature Comparison of brake-fluid perform• Finding a brake can withstand without failure. at high temperatures. ance

Comparison of brake-fluid performance at high temperatures.

• Testing different types of calipers, brake drums or other hardware. different of calipers, • Testing Comparison of types different ro tor brake drums or other hardware. designs . Comparison rotor • Testing effectof ofdifferent caliper-piston designs. insulators. effect oftorque caliper-piston Finding maximum the brake • Testing insulators. is capable of achieving without strucFinding torque the brake tural failuremaximum .

is capable of achieving without structural failure. .TESTING COMPONENT

Manufacturers do a lot of brakeCOMPONENT TESTING system-part testing. They test master Manufacturers do cylinders a lot of on brakecylinders and wheel test system-part testing. They test master rigs that automatically apply the cylinders andand wheel test brakes over over.cylinders This testsondurarigs that automatically apply the bili ty of the parts. brakes over over. cylinder This tests duraBy cyclingand a brake rapidly, bility parts. much less time than testingof the takes By testing. cycling aInbrake cylinder rapidly, track addition , components testing takes much less time subjected to internal pressure than are track In addition, components testedtesting. for bursting strength at pressubjected internalthanpressure sures muchto higher normal. are It tested for bursting strength must be proven that each itemathaspresthe sures much higher than It strength to withstand the normal. maximum must be proven that each item has the possible pressure and have a signifistrength withstand the maximum cant factortoofsafety. possible a signifiIf youpressure wish and to have pressure-test cant factor of safety. components, it is not difficult to set you You wishmustto getpressure-test upIfa test. a hydraulic i t is not difficult to seta components, pump or build a lever to operate

up a test. You must get a hydraulic pump or build a lever to operate a 105

Complete line of temperature-measuring instruments is offered by Omega Engineering, Inc. Digital meters shown are designed to be used with By combininginstruments a meter with a therComplete linethermocouples. of temperature-measuring is offered mocouple in a Inc. special probe, you shown C:ln custom-build your by Omega mounted Engineering, Digital meters are designed to own pyrometer. Such instrumentation is useful for testing on a be used with thermocouples. By combining a meter with a therbrake dynomounted or race car. courtesy mocouple in aPhoto special probe, Omega you canEngineering. custom-build your

own pyrometer. Such instrumentation is useful for testing on a brake dyno or race car. Photo courtesy Omega Engineering.

Handy pyrometer kit is manufactured by AP Racing and sold by Tilton Engineering. It comes with two probes; one for soft materials such as tires, kit andisone for hard materials as brake rotors. Handy pyrometer manufactured by APsuch Racing and sold by Instrument can be used to measure brake temperatures on mateopenTilton Engineering. It comes with two probes; one for soft wheel cars.asPhoto AP hard Racing. rials such tires, courtesy and one for materials such as brake rotors.

Instrument can be used t o measure brake temperatures on openwheel cars. Photo courtesy AP Racing.

Indicator Mount

---Force

! tp,,,, Caliper

Master Cylinder or High-Pressure Pump

Master Cylinder or Pressure High-Pressure Caliper pressure-test setup: gage Pump should have minimum 1S00-psi range; 2000 psi is preferable. If maximum pressure is exceeded, gage will be damaged. Spacer gives something for pads to push against. Notegage how should dial indicator is mounted: Bracket is attached Caliper pressure-test setup: Pressure have minimum 1500-psi range; 2000 to side of caliper and gagepressure is set square against oPPosite so it will read totalgives calipsione is preferable. If maximum is exceeded, gage willside be damaged. Spacer per deflection. Test to can alsoagainst. be performed on the if a pressure gage Bracket is installed in brake something for pads push Note how dial car indicator is mounted: is attached line. Remove before avoid excessive pedal travel. to one side ofgage caliper and driving gage iscar settosquare against opposite side so it will read total caliper deflection. Test can also be performed on the car if a pressure gage is installed in brake line. Remove gage before driving car t o avoid excessive pedal travel.

brake master cylinder. The lever can be operated by hanging weights on a brake pulley master system.cylinder. You can The then lever applycan an be operated by hanging weights on a exact load to the master-cylinder pulley You can itthen an pushrodsystem. and maintain so apply you can exact load to the master-cylinder make measurements . pushrod Deflections-It and maintain itis so you can System interesting make measurements. to test the deflection of hydraulicSystem components Deflections-It interesting system whileis the system to test the deflection of is pressurized . Of particular hydraulicinterest is system components while the deflects system how much a caliper is pressurized. Of particular interest is outwardly. You can measure this dehow much a indicator caliper mounted deflects flection with a dial

outwardly. You can measure this deflection with a dial indicator mounted 106

to the caliper. You must also measure either hydraulic pressure in the to the caliper. must also measure system or forceYou on the master-cylinder either hydraulic pressure in the piston. System pressure can then be system or force on the master-cylinder calculated. A hydraulic-pressure gage piston. System pressure can do then with a large-enough scale will it. be calculated. A hydraulic-pressure gage An engine oil-pressure gage won 't with a large-enough scale will do it. have enough capacity. Relatively inexAn engine gage psi won't pensive gages oil-pressure reading to 2000 are have enough Relativelystores. inexavailable at capacity. industrial-supply pensive gages reading to 2000' s psi are Marsh Instrument Company J4878 available at industrial-supply stores. pressure gage is a 2000-psi gage that Marsh Instrument Company's J4878 uses minimum displacement.

pressure gage is a 2000-psi gage that uses minimum displacement.

Put a tee in the hydraulic line and install the gage. Make sure air cannot a tee inin the the gage hydraulic line high and bePut trapped or other installinthethe gage. Make sure air cannot spot system. Pressurize the be trapped the gage or other high system and inrecord caliper deflection spotincremental in the system. Pressurize pressures. Drawthea at systemofand recordversus caliper deflection pressure deflection . It graph at incremental pressures. a Draw should be approximately straighta graph of pressure deflection. It line. If it's not, versus something in the should be approximately a straight system has slack, which is being taken line. it's not, issomething in the up, orIfsomething failing. Check to system has deflection slack, whichreturns is beingto taken see if the zero up, orpressure something is failing.If Check to when is removed. some desee if the deflection returns to zero flection remains without pressure, when pressure is removed. If some desomething has bent or crushed . flection remains without pressure, You can measure brake-hose and something has bent or crushed. These deflecline deflection as well. You can measure tions are small, but brake-hose you should and be line well. with These defleca dial inable deflection to measureasthem tions arewhile small,us ing but extremely you shouldhigh be dicator able to measure them with a dial insystem pressure. Take a number of dicator while just using extremely high measurements to be sure.

system pressure. Take a number of measurements just to be sure. THE TEST TRACK

The only way to get the most from a

THE brake TEST systemTRACK is to test it on the car. The only way to to get You don ' t have testthe on most a racefrom track.a brake to test itbrake on the car. Unlikesystem chassisis testing, testing You have tointest a race track. can don't be done a on straight line. Unlike chassis Therefore, youtesting, may brake have testing more can be done in a straight line. options. Therefore, havehasmore Each area you of themay country difoptions. ferent facilities and laws. List possible Each locations area of the country difdon'thas forget testing so you ferent facilities and laws. List possible any. Pick the one most suitable for testingpurposes. locationsDon't so you don'ttheforget your ignore legal any. Pick the oneas most for limitations, such noise suitable ordinances. your purposes. Don't ignore the legal People next to your " test track" may limitations, such noiseofordinances. not appreciate the as sound screeching People next to your "test track" may not appreciate the sound of screeching

ｾＧｭｺｯＢＬ＠ Caliper Deflection (in) Caliper Deflection (in.)

When testing a race car's brakes, do it on the same type of track it will run on. This track is best for testing oval-track When testing a race car'sanbrakes, do itdirt on car. same It's not much good for testing a roadthe type of track it will run on. This racing is car. track best for testing an oval-track dirt car. It's not much good for testing a roadracing car.

Hydraulic Pressure (psi)

Hydraulic Pressure (psi) Use data obtained from caliper-deflection test to plot pressure-versus-deflection curve. Curve should be a straight line. If deflection increases at a faster rate at high pressure, something in the system failing. Don't risk test trouble brakes in the problem zone. Use data obtained from is caliper-deflection to by plotusing pressure-versus-deflection curve. Curve should be a straight line. If deflection increases at a faster rate at high pressure, something in the system is failing. Don't risk trouble by using brakes in the problem zone.

Stock car has pressure gage mounted on brake line next to each master cylinder. pressures, an Stock carBy hasrecording pressure gage mounted exact numerical record brake balon brake line next to of each master ance is available. Don't ,l eave pressure cylinder. By recording pressures, an gages numerical in hydraulic system because exact record of brake balthey increase pedal travel. ance is available. Don't leave Pressure pressure gages testing only. gages are in for hydraulic system because they increase pedal travel. Pressure gages are for testing only.

WARNING High-pressure testing is used WARNING only to find the limits of a design and High-pressure testing determine its safety factor.is If used you to finda the limits ofpump a design and onlyusing are hydraulic capable determine If you 3000 psiitsorsafety more, factor. you may be of are a items hydraulic pumpbecause capable to failure ableusing to test of 3000 psisystems or more,operate you may be most brake below able test itemsistosome failure because 1500topsi. There danger asmost brake systems operate so below sociated with such testing, be danger as1500 psi.Air There is some in the system careful. trapped sociated with such testing,force. so be explosive If can escape with careful. Air trapped theflying system parts break, they canin go at can escape with explosive force. If parts break, they can go flying at

tires, even if you think your testing is strictly legal. tires, even if you think your for testing is Some possible locations brake strictly legal. testing are: possible locations fortesting. brake • Some Road-racing track rented for

testing are: Road-racing track rented for testing.

high velocity. Isolate people from the items being tested, and make high tovelocity. from thesy.stem. sure bleed allIsolate air frompeople the items being tested,before and make Always relieve pressure looksure bleed all air from the system. ing attothe parts. Always pressure before lookIf yourelieve pressurize a part to three ing at the times its parts. maximum rated capacity If you pressurize to three and it does nbt fail aorpart distort, it is times its maximum rated .all capacity well designed. However, parts and it does fail or distort, it is tested to not excessive pressures well designed. However, all parts should not be used. They should be tested pressures marked permanently destroyedto or excessive should be used. TheyThere shouldmay be for easynotidentification. destroyed marked permanently be damageorhidden from view that for easy There makes the identification. part unsafe to use . . may beIf damage viewrig that you are hidden makingfrom a test for makes the part unsafe use. 3000to psi, go to an pressures up to If you are making a test rig Airfor aircraft-surplus shop for parts. pressures up tosystems 3000 psi, go to an craft hydraulic operate at aircraft-surplus shop for their parts.highAir3000 psi. Consequently, craft hydraulic systems operatecan at pressurehbses and fittings 3000 psi. pressure. Consequently, their take this Check withhighthe pressure andgetfittings can shop to be hoses sure you parts rated take3000-psi this pressure. Check the for pressure. Handwith pumps shop to bepressurize sure you get rated that can a parts system to for 3000-psi pumps 3000 psi arepressure. available.Hand You'll also that pressurize to 3000-psi need can pressure gages aforsystem 3000 psi are available. You'll also capacity. need pressure for lines 3000-psi Before using gages surplus and capacity.wash them throughly with fittings,. Beforeto using lines and alcohol removesurplus dirt, moisture fittings, them throughly with aircraft wash hydraulic fluid. Aircraft alcohol to remove dirt,different moisturefrom and brake fluid is totally aircraft hydraulic fluid. Aircraft start automotive brake fluid. Always brakeclean fluidcomponents. is totally different from with automotive brake fluid. Always start with clean components.

,

• Drag strip rented for testing. • Large parking lot. Dragairport, strip rented for testing. • An particularly one with Large parking lot. light air traffic or unused runways . An airport, one with, • Straight road particularly away from residences

light air traffic or unused runways. Straight road away from residences,

intersections and with little traffic. Race Tracks-Obviously, the best intersections with place to test and a race carlittle is atraffic. race track Race Tracks-Obviously, the best like the one you will compete on. place to test a race car is a race Even for testing a road car, a track race like one advantages you will compete on. track the has the of safety and Even testing road are car,available a race privacy.forSome race atracks track hasthetheweek advantages of safety fee and. during for a nominal privacy. Some race tracks are available You should be prepared to bring whatduring the week for a nominal fee. ever safety equipment the track You should be prepared to bring whatrequires, even if you consider brake ever equipment the track testing safety much safer than going flat-out. requires, even if you consider brake Chances are that track management testing much safer than going flat-out. and insurance companies won't make are that track management anyChances distinction between one type of and insurance companies won't they'll make driving and another. Usually, any distinction between one type of require the driver to wear a helmet driving another. Usually, and use and other standard racing they'll safety require the driver to wear a helmet equipment. You and all those inand use other standard racing safety volved may also have to sign a waiver equipment. and of all allthose that relieves You the track legal inrevolved may ifalso have tois sign a waiver sponsibility someone injured. that relieves the track of all legal car, reIf you are testing a road-racing sponsibility if someone is injured. you should test on a road course . The If you are testing same holds true fora road-racing other typescar, of course. The you should test on cars. Oval-track carsa road should be tested same holdstrack-dirt true for cars otheron types of on an oval dirt and cars. Oval-track cars should be tested pavement cars on a paved on an oval track-dirt dirt and and track-dragsters on a cars drag on strip, pavement on will aallow paved on down the cars line. This you track-dragsters on a or drag and to run the car around up strip, and down on down the line. This will allow you the track many times in succession to runtest thethe car brakes around for or up and down and temperature the track in succession and wear many undertimes simulated racing and test the brakes for betemperature conditions. This will not possible at and wear under simulated other types of test tracks. If youracing can't conditions. This will not be possible at test on a race track, you'll have to use other types tracks. If"you can't. actual racingof fortest "real-world testing test on a racea track, to use Although drag you'll strip ishave ideal for actual racing for "real-world" testing. testing a drag-car brake system, one is Although a drag strip is ideal also useful for testing other types for of testing a drag-car brake system, is cars. You can do one stop one from also useful for types of moderately hightesting speed other at a drag strip. cars. can allows do one stop Or, if You the track , you canfrom run moderately high speed at a drag strip. several stops in succession by running Or, the track you can run backif and forth. allows, Usually , there is

several stops in succession by running back and forth. Usually, there107 is

Drag strip can be used to test brakes at medium to high speeds. Dragster reaches top speed in quarter mile, so its brakes get a realistic workout. will only reach about two-thirds Drag strip can be Typical used toroad testcar brakes at medium to high speeds. of its maximum Regardless, dragmile, strips usually get safe Dragster reachesspeed. top speed in quarter so are its brakes a and handy for brake testing. realistic workout. Typical road car will only reach about two-thirds

Small airports are potential brake-test sites. However, you must first get permission from the airport manager.

Small airports are potential brake-test sites. However, you must first get permission from theairport manager.

of its maximum speed. Regardless, drag strips are usually safe and handy for brake testing.

plenty of room to bring the car to a safe stop. plenty room to of bring the strip car toarea The of advantages a drag safe stop. that it will be clean , smooth and level. The advantages of aconsiderations. drag strip are These are important that it will be clean, smooth and level. The problem with a drag strip is its These are important considerations. length. You usually can't get a car Tnear h e problem with speed a draginstrip is its its maximum a quarter length. You you usually get a a drag car mile, unless are can't running near its maximum speed in a quarter racer. Most road cars reach about twomile, you are running a drag thirds unless maximum speed in a quarter racer. Most road cars reach about twomile. This represents about one-half thirds maximum kinetic speed in a quarter of the maximum energy a car mile.deliver This represents about one-half can to the brakes. Thus, testof the maximum kinetic energy a car ing at a drag strip leaves some doubt can deliver the brakes. Thus, of test-a about the to ultimate capability ing at system. a drag strip leaves some doubt brake about thecan't ultimate of a If you rent capability the drag strip, brake system. enter the car in a drag race . You may you can't be Ifallowed to runrent time the only, drag wherestrip, you enter car in a drag competition. race. You may don't the engage in actual If time hard only,at where be allowed to run you apply the brakes the you end don't in actual competition. If of the engage strip, you can get some idea of you the brakes hard at the end how apply the brakes work at medium-high of the strip, you can get some idea of speeds. how the racing brakes will worklimit at medium-high Drag testing bespeeds. cause carrying an observer during Drag will be limit testingAlso, beeach runracing may not allowed. causewon't carrying observer during you be ableanto get as many runs each maytest notsession. be allowed. Also, as in arun private you won't be able to getlots as many runs Parking Lots-Parking are someas in a private test session. times available on weekends. The Parking is Lots-Parking lotsenough are someproblem finding a lot big for times available on weekends. The testing brakes. Most are too small. problem is finding a lot problems big enoughwith for Also, you'll run into testing brakes. too small. dirt, bumps and Most nearbyare people. And, Also, run into with it may you'll be difficult to getproblems permission to dirt, bumps and nearby people. And, use a really large lot because they are it may beowned difficult get permission to usually by to large corporations. use alarger reallythe large lot because they difare The company, the more

usually owned by large corporations. The 108 larger the company, the more dif-

ficult it will be to talk to the individual who makes the decisions. ficult it will talk to lot the to individual If you findbeatoparking run on, who makes the decisions. be aware of the legal and safety If you find aAlways parking run lot to run on, requirements. a muffled be aware of the legal and safety exhaust, unless you are really out in requirements. Always run a muffled the "sticks." Test during hours when exhaust, unless are really If outyou in people will not you be disturbed. the permission "sticks." Test when get to during use thehours lot, try to people not be disturbed. If you get it inwill writing. Invite the person in get permission to use the lot, to charge to attend your test session.tryNot get writing. Invite person in onlyitisinthis good PR, butthe if the police charge he to attend your testasession. Not come, can give them good story. only is athis good PR, but if the police Often, well-meaning bystander will come, he can give them a story. call the police, because he'sgood not aware Often, obtained a well-meaning bystander will you've permission . call the police,large because he'ssurface not aware Airports-A testing can you've obtained permission. be found at an airport. The runways Airports-A large testing surface can are always long and usually smooth, be found at an airport. The runways level and relatively clean. The best are smooth, placealways to try long is a and smallusually airport, which level and relatively clean. The best may be used occasionally by private place to try is a small airport, which planes. They may have a runway not may beorused occasionally private in use, possibly an accessbyroad that planes. They may have a runway not. can be closed temporarily for testing in use, or possibly an access road that It helps if the airport manager likes can closed temporarily forask testing. race be cars. Don't be afraid to . You It helps the airport manager likes might be if pleasantly surprised. race cars. Don't afraid to ask. You Airports havebethe advantage of might be pleasantly surprised. minimal noise problems and a lot of Airports havehave theto advantage of room . You may sign a waiver minimal and a lot of to releasenoise the problems airport management room. responsibility. You may have Also, to signthey a waiver from may to release the airport management want proof of insurance. If you are from responsibility. Also, they may professional in your approach to want insurance. If you are testing,proof it willofhelp a great deal. professional in you yourhave approach to Public Roads-If a road cat, testing, it will help a great deal. you can try a pu blic road as the last Public ItRoads-If you to have car,a resort. may be legal stopa aroad car in you can line try if a public as the last straight you do road it safely. If you

resort. It may be legal to stop a car in a straight line if you do it safely. If you

do not speed , make excessive noise or appear to be driving recklessly, you do excessive noise or maynot bespeed, able tomake convince a police offiappear to be driving recklessly, you cer to allow you to test. It helps to be mayfrom be able to convince police. offifar houses and other apeople cer to allow you to test. testing It helps while to be Race Testing-Brake far from houses and other people. running a race can be done as a last Race testing while resort. Testing-Brake If you do this, pick an event running a race can be done as atime last that offers maximum practice resort. If you do this, pick an event and mlntmum competition . For that offersa local maximum practice time example, drag event is much and minimum competition. better than a championship event. For For example, a local event is much road racers, try a drag solo-I or time trial better event. For rather than than a achampionship race. In solo-I events, road racers, try a solo-I or time trial the cars run one at a time. The practice rather than a race.quite In solo-I events, sessions are often long. Another the carsisrun at athe time. option to one enter carThe in practice. a racesessionsschool. are often quite driving But firstlong. , get Another permisoption is the to enter the car in a race-. sion from sponsoring organization

driving school. But first, get permission from the sponsoring organization. PLANNING BRAKE TESTS Plan your tests before you get to the

PLANNING TESTS If you track. Testing BRAKE time is valuable. before the Plantoyour testswork have do any on you the get car to other track. Testing time is planned, valuable. Ifyou'll you than what you've have to do on the car waste other probably runany outwork of time. Don't than what you've planned, you'll time trying to think up what to do probably out. Plan of time. Don't waste next at therun track ahead. time to thinkdown up what do Starttrying by writing yourto test Plan ahead. next at the track. plan. List what you'll be testing for. Start by writing down test Include a step-by-step planyour of how plan. List whattesting. you'll be testing for. you'll do the While writing Include step-by-step of how the test aplan , think of plan all the test you'll do the tools testing. writing instruments, and While parts needed the test plan, think of all the to do the job . List these separately.test A instruments, tools isand parts onneeded sample test plan shown page to doItthe List separately. A 109. willjob. give youthese an idea of what's sample test plan is shown on page needed . Determine exactly what's 109. It will giveplan. you an idea of what's needed in your needed. Determine exactly what's Data Sheets-In addition to the test needed in your plan. Data Sheets-In addition to the test

SAMPLE TEST PLAN

SAMPLE LIST OF BRAKE- TESTING EQUIPMENT

1. 2. 1.

Inspect brakes and record starting data . SAMPLE TEST PLAN Overall brake-performance test. lnspect brakes and record data. a. Record comments on starting performance. 2. Overall brake-performance test.as required. b. Inspect and adjust brakes a. Record comments on performance. 3 . Balance adjustment tests. b. Record lnspect deceleration and adjust brakes required. beforeassetting balance. a. 3. Balance adjustment b. Test brakes andtests. adjust balance. Record deceleration before setting balance. . a. c. Continue until maximum deceleration is attained. b. Test brakes 4. Cooling-duct testsand . adjust balance. c. Continue maximum deceleration is attained. a. Tuft tests until to confirm airflow in duct. 4. Cooling-duct b. Measuretests. brake temperature after one stop. a. tomeasured confirm airflow in duct. car for time and measure cooling effect. c. Tuft Run tests b. Measure brake temperature one stop. d. Modify ducts and test coolingafter again. c. Runlining car fortests, measured time and measure cooling effect. 5. Alternate d. Modify fluidducts tests.and test cooling again. 6, Alternate 5. Alternate liningtesting, tests. 7. Long-distance 6. Alternate fluid tests. a. Check temperature. 7. Long-distance testing. b. Check wear rate after test. a. Recordtemperature. driver comments and results of brake inspection, c, Check b. Check rate 8. Bed-in sparewear linings forafter nexttest. race . Record driverwith comments and results of brake inspection. balance wings adjusted to maximum downforce settings, 9 . Setc.brake 8. Wet Bed-in spare linings forrain nexttires, race.and balance brakes for wet. 10. down track, install

SAMPLE OF work on car. • Tool box LIST for general BRAKE-TESTING for driver, fire • Safety equipment EQUIPMENT Tool box for general work on car. extinguishers. Safety equipment driver, and fire • Spare parts for forengine extinguishers. chassis, parts for engine and • Spare Spare tires and wheels. chassis. • Brake linings, brake fluid, special Spare tires and wheels. brake-maintenance tools. Brake linings, brake fluid, special ｴ･ｭｰｲ｡ｵｾｩｮ､｣ｧ＠ • Pyrometer, brake-maintenance tools. labels, temperature-indicating paint. Pyrorneter, temperature-indicating • Stopwatch. labels, temperature-indicating paint. • Toppling.block setup. • Stopwatch. Yarn for tufts, tape, scissors. setup. • Toppling-block Video camera, still camera, portafor tufts, bleYarn TV and VCR. tape, scissors. camera, stilltank. camera, porta• Video Fuel, oil, water, air TV and VCR. ble • Jack,jack stands, creeper. oil, water, tank. Materials for air modifying brake • Fuel, Jack,racer's jack stands, ducts, tape, creeper. rivets and rivet Materials for modifying brake gun. ducts, racer's tape,pen. rivets and rivet • Notebook, paper, gun. Notebook, paper, pen.

plan, make several copies of the blank data sheet on this page for recording plan, make copies o f the blank test results.several Pertinent information data sheet on this page for recording about the exact brake-system setup test results. Pertinent should be included: type information of linings, about balance-bar the exact brake-system setup fluid, setting, and similar should be included: type o f linings, information. These will be valuable fluid, tobalance-bar and similar facts determine setting, what setting caused information. These will be valuable what to happen. facts to determine what on setting caused Recorded comments brake perwhat to happen. formance versus temperatures are Recorded comments brake pervital. If you are recordingo ndeceleration formance versus temperatures are rates, make a form for that, too. you are recording deceleration vital. I f test-data These forms can also be rates, make a to form for car that, too. useful at a race record settings These test-data forms can also be and compare them to actual performuseful a race ance onatthe track.to record car settings and compare them to actual ListsYou can never bringperformenough ance on the track. tools or parts to a test session. If you Lists-You cantool never bring you enough leave a part or at home, can you tools or it's parts a test session. be sure thetoone you'll need. IfMura part or tool at home, you can leave phy's Law always applies. beMake sure it's the one you'll need. Mand ura list of tools, supplies phy's Law always instruments. Addapplies. to these lists anyMake a list for o f car tools, supplies and thing needed maintenance or instruments. Add to these liststhings anyrepair. Bring spare parts for thing to needed car have maintenance or likely break.for If you room, also repair. Bring spare parts things bring everything that's notforlikely to likely break.to break. I f you have room, also bring everything not likelyinto to Organize parts that's and supplies break. sturdy boxes and label them. This will Organize and supplies into make taking parts everything much easier. sturdy boxes and label one them. pit Thiscrew will If possible, assign make taking everything much easier. member to keep track of things, and If possible, one pit after crew put everything assign back immediately member to keep track team o f things, and use . A well-organized is a must putsuccessful everythingtesting back immediately for and racing. after well-organized team is sheets, a must use. PutAyour test plan, test-data for successful testing and racing. and parts and supplies lists into a notePutconsisting your test plan, test-data sheets, book of a three-ring binder and parts and supplies lists into a notebook consisting o f a three-ring binder

9. 10.

Set brake balance with wings adjusted to maximum downforce settings. Wet down track, install rain tires, and balance brakes for wet.

HPBooks® BRAKE TESTING DATA SHEET Car _ _ _ Date _ _ 1, Brake System Specification, Date A, Balance-bar setting _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ __ _ _ 1 . Brake System Specification. B, Proportioning-valve setting _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ __ A. Balance-bar setting C. Lining material: Brand _ _ ___ (Front) _ _ __ ___ (Rear)

HPBooksmBRAKE TESTING DATA SHEET Car

I

B. Proportioning-valve setting

D. Brake fluid : _______ Brand _ ______ Type

C. Lining material: Brand

(Front)

I

(Rear)

E, Rotor diameter & thickness: _ _ _ _ _ _ _ (Front) _ _ _ _ _ _ (Rear)

D. Brake fluid:

Brand T

y

p

e

F, Caliper brand & type: _ _ _ _ _ _ (Front) _ _ _ _ (Rear) (Front) (Rear) 2, Brake performance , & type: (Front) -(Rear) F. Deceleration Caliper brandreadings, A. 2. Brake performance. B, Comments on each test. A. Deceleration readings. C. Tires used, size and brand _ _ _ _ _ _ _ (Front) _______ (Rear)

E. Rotor diameter & thickness:

B. on each test._ __ __ (Weather) _ _ _ _ __ _ _ D, Comments Road condition _ __ C. Tires used, size and brand (Front) (Rear) E, Comments _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ D. Road condition (Weather)

3. Temperature testing,

I I

(Front)

E. Comments Maximum caliper 3. A. Temperature testing.temperature

(Front)

(Rear)

.

(Rear)

B, Maximum rotor-edge temperature A. Maximum caliper temperature C. Maximum hub temperature

I I

B. Maximum rotor-edge temperature

D. Maximum lining temperature

C. Maximum hub temperature

I I 1

E, temperature D. Maximum lining temperature F, Comments _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ __ temperature E. testing. 4. Wear (Front) (Rear)

F. Comments

A, Lining thickness-beginning 4. Wear testing. B, Lining thickness-ending C, Wear (beginning/ending) B. Lining thickness-ending D, Test duration _ _ miles, _

C. Wear (beginning/ending)

1

I

(Front)

(Rear)

A. Lining thickness-beginning

_

laps, _ _ stops @ _ _ mph

E, Test track Conditions _ _ _ D. Test duration -miles, -laps, -stops @ -mph F. Comments _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ _ _ _ _ _ __ E. Test track Conditions -

F. Comments or similar record-keeping system, Bring a clipboard to write on, Keep or similar record-keeping the notebook with you during system. all tests Bringraces; a clipboard write on. Keep and put all to technical informathe notebook with you during all tests and races; put all technical informa-

I

tion in it. The notebook will becomeI your "bible " after a year or so . Betion in test it. The will become cause datanotebook is valuable, make your after a year so. Becopies"bible" of everything whenor you '!et cause test data is valuable, make copies o f everything when you n_et 109

Pyrometer is used to measure brake temperature on open-wheel race car. This is difficult on full-fendered cars. When checking temperature, quickly hold pyrometer probe firmly against rotor until meter needle stops rising. Peakontemperature braking cannot be pyrometer is used to measure brake temperature open-wheelduring race car. This is difficult on full-fendered cars. When checkingbecause temperature, quickly will holdoccur. pyrometer probe firmly measured with hand-held pyrometer some cooling Peak temperature can only rotor be measured withneedle an on board or temperature-indicating label or paints. against until meter stopspyrometer, rising. Peak temperature during braking cannot be measured with hand-held pyrometer because some cooling will occur. Peak temperature can only be measured with an onboard pyrometer, or temperature-indicating label or paints.

Omega Engineering Inc. specializes in temperature-measuring devices. Some of their paint and Omegatemperature-indicating Engineering Inc. Specializes in labels are shown here.devices. Photo courtesy temperature-measuring Some of Omegatemperature-indicating Engineering. their paint and labels are shown here. Photo courtesy Omega Engineering.

0-800C (32-1472F) range. It is useful for checking both tire and (32-1472F) range. It is 0-800C brake temperatures. The liquid-crystal useful allows for checking tire ease and used with display it to be both brake temperatures. The liquid-crystal in the sunlight. There are two display allows it to be for usedtires withand easea probes-a sharp one in the There are flat one sunlight. for hard surfaces suchtwo as probes-a sharp oneI for tiresrecomand a brake components. highly flat surfaces suchserias mendone suchfor an hard instrument for the brake components. I highly recomous racer. I t can also be used fo r. mend such an instrument the seriengine tuning, such asfor checking ous racer. It can be used for. which exhaust pipe also is running hotter engine tuning, such as checking or cooler than the others. which exhaustwhen pipe using is running hotter Remember a hand-held or cooler thanthat the others. pyrometer the object being Remember whenrapidly. using aTherefore, hand-held checked will cool pyrometer that the object it must be measured quickly being after checked cool rapidly.isTherefore, maximumwilltemperature reached. it must be measured quickly after Unfortunately, it is impossible to maximum temperature is reached. measure the peak temperature of an Unfortunately, is impossible to iron brake rotorit with a hand-held measure peak of an pyrometer.theBut youtemperature can come close if iron work brake rotor with a hand-held you quickly. pyrometer. ButIndicators-You you can come close Temperature mayif you work quickly. find that it's easier to use temperature Temperature Indicators may indicators rather than a -You pyrometer. find that easiertypes to useof temperature There areit's several indicators. rather changing than a color pyrometer. indicators Some are paint, when There are several types of indicators. they reach a certain temperature . DifSome are color atwhen ferent colorpaint, paintschanging change color difthey reach a certain temperature. Different temperatures, so by using variferent color the paints change color at difous colors, peak temperature can ferent temperatures, so by using varibe found. ous colors, peak temperature can One line the of temperature-indicating be found. paint is available from Weevil Ltd . in One line of Tempil temperature-indicating Europe. Also, has a complete paint is available from Weevil includLtd. in line of temperature indicators,

ing Tempilaq temperature-indicating paint. Another is sold by Tilton ing TempilaqUsually, temperature-indicating Engineering. these paints are paint. Another is soldofby the Tilton brake applied to the periphery Engineering. Usually, these paints are rotor. They can be used on the caliper applied to the periphery of the brake body as well. rotor. They temperature can be used on the caliper Another indicator is a body as well. stick-on label. These are sold by Another temperature is a Tempil (Tempilabel) andindicator Omega Enstick-on label. These are sold by gineering Products (Omega Label), Tempil (Tempilabel) and Omega Enrespectively. gineering Products (Omega Label), These adhesive-backed labels have respectively. white spots that turn black at increThese temperatures adhesive-backed have mental , aslabels indicated white that turn black at on increnext tospots each spot: If some spots the mental as do indicated label turntemperatures, black and others not , a next each spot: If was somereached spots on the bepeak totemperature label turn black and others not, a tween the values of the dohighestpeak temperature wasandreached betemperature black spot the followtween thespot. values theturnhighestwhite If all of spots black , ing temperature black spot andonthethefollowthe highest temperature label ing white spot. spotsa turn case,black, you was exceeded. IfInallsuch the temperature on the label needhighest the next higher-temperature was case,black you, label exceeded. available. IfInnosuch spot aturns need the next higher-temperature the temperature of the lowest spot label available. If In no this spotcase, turnsgoblack, reached. to a was not the temperature oflabel. the lowest spot lower-temperature was not areached. In this go to a Have wide range of case, temperature lower-temperature label. indicators for your first test. You Have a have wide no range temperature idea ofwhat the temprobably indicators for your test. perature ranges will be.first Once youYou get probably have no idea what the temsome experience, you'll know which perature ranges will be.toOnce temperature indicators use . you get some experience, which If you want to be you'll able to know get accurate temperature indicators to use. peak and non-peak temperature readIf you want stopping to be able the to get accurate ings without car, you ' ll peak non-peakpyrometel; temperature readneed and a remote a multi-

home. Store the copies somewhere other than in the notebook. Notehome. get Storelost, the particularly copies somewhere books at the other than in the notebook. Noteraces. books get bring lost, particularly at the Finally, as many qualified races. helpers as possi ble, and all the equipFinally, bring you as ' llmany ment you think need . qualified Include helpers as possible, and all the equipthe required safety equipment. Even ment Include if you you are think testingyou'll in a need. straight line, the helmetequipment. and drivingEven suit. bringrequired a crash safety if you testing a straight line, never be tooincareful. You canare

bring a crash helmet and driving suit. You can never be too careful. BRAKE-TESTING INSTR UMENTS BRAKE-TESTING Certain instruments are needed to INSTRUMENTS get maximum benefit from a test Certain Of instruments are needed to session. primary importance is get benefit a test temperature. It can from be measured brakemaximum session. Of aprimary importance is with either hand-held pyrometer, brake temperature. It can be measured remote pyrometer or with temperature with either a hand-held pyrometer, indicators on the brake . placed remote pyrometer pyrometer or with temperature Pyrometer-The is a speplaced on Itthehas brake. indicators thermometer. a probe that cial Pyrometer-The pyrometer is aTemspecan be placed against an object. cial thermometer. It has a probe perature is then read from a meter.that A can be placed against anused object. Tempyrometer is commonly to measperature is then from a meter. A ure race-car tire read temperatures. It can pyrometer is commonly used to measalso be used to measure brake temure race-car tirethetemperatures. can perature up to limit of the It meter also beThe used to measure brake temscale. pyrometer-probe tip must perature to contact the limitwith of the meter be held inupfirm the object scale. The pyrometer-probe tip into being checked so heat can soakmust be in firm contact with stabilizes, the object theheld probe. When the meter being checked so heat can soak into the reading is taken and recorded. theAnprobe. Whendual-purpose the meter stabilizes, excellent pyromethe taken and sold recorded. ter reading is AP's is CP-2650-8 by Tilton An excellentThis dual-purpose pyromeEngineering. instrument has a ter is AP's CP-2650-8 sold by Tilton Engineering. This instrument has a

110

Europe. Also, Tempil has a complete line of temperature indicators, includ-

ings without stopping the car, you'll need a remote pyrometel; a mirlti-

ap: RACinG Excellent temperature indicators are manufactured by Tempil. Tempil's Tempilaq paint meltstemperature when heated to rated Excellent indicators are temperature. Tempilabel spots turn black manufactured by Tempil. Tempil's Tempilaq when heated rated temperature. paint melts towhen heated to Photo rated by Tom Monroe. temperature. Ternpilabel spots turn black when heated to rated temperature. Photo by Tom Monroe.

position switch and thermocouples to put in contact with the test objects. A position thermocouples to full lineswirch of and remote temperatureput in contact with the test objects. A measuring equipment, including therfull line ofandremote mocouples leads, temperatureis available measuring equipment, including from Omega Engineering Productsther. mocouples and leads, is available Their 12-volt model 650K digitalfrom Omega Engineering readout pyrometers areProducts. relatively Their 12-volt digitalcompact and aremodel easy 650K to read . All readout pyrometers are relatively digital-readout pyrometers require excompact and are easy toseries-7000 read. All ternal power. Omega's digital-readout pyrometers pyrometers require exdial-readout are selfternal power. Omega's powered, compact and lessseries-7000 expensive dial-readout pyrometers areto selfthan digitals, but not as easy read powered, compact and less expensive accura tely. than digitals, butElectronic not as easySystems' to read Nationwide accurately.II digital-readout pyrometer Slimline Nationwide Electronic12-volt, Systems' IDT-7726 is compact, d-c I1 digital-readout pyrometer Slimline powered, and is easy to read. It reIDT-7726 is compact, d-c 12-volt, d-c quires a 100-0193-01 isolator powered, andsure is easy to read.type-K It remodule . Be to specify quires a 100-0193-01 d-c isolator thermocouples when ordering. Also module. Be sure to specify type-K specify whether you want a pyrometer thermocouples when ordering. Also that displays temperature in Fahrenspecify whether you want a pyrometer heit or Centigrade. that displays temperature in FahrenThermocouple Installation - Therheit or Centigrade. mocouple attachment is important. Thermocouple -Ther-be The thermocoupleInstallation junction must mocouple important. in contact attachment with the istest object. The thermocouple must be Otherwise , readings junction will be low. Highin contact with the test object. temperature epoxy works well for atOtherwise, readings will betolow. Hightaching thermocouples calipers. temperature epoxy works well for atThermocouples can be pinched under taching thermocouples to calipers. the head of a screw. Or, silver solderThermocouples be pinched under ing works well oncan some metals. Whatthe head solderever you of usea, screw. be sureOr, thesilver attachme nt ing worksinsulate well on some Whatdoesn't the metals. thermocouple ever you use,object. be sure the attachment from the test doesn't insulate the isthermocouple Rotor temperature difficult to from the test measure withobject. a thermocouple. The

Rotor temperature is difficult to measure with a thermocouple. The

As with other temperature-indicating paints, AP Racing's indicators can be used to check rotor or brake-drum temperature. Temperature indicators will tell you the highest tempera·· ture reached, you use the right range paints, of paints. Racing. can be used to check As with other iftemperature-indicating APCourtesy Racing's AP indicators rotor or brake-drum temperature. Temperature indicators will tell you the highest temperature reached, if you use the right range of paints. Courtesy AP Racing.

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Drawings show how to install thermocouple plugs in disc and drum-brake linings so brake temperatures can be monitored while running. For this purpose, you can make your own type-K thermocouples twisting chromel and alumel and linings silver soldering Drawings show how to by install thermocouple plugs in discwire andtogether drum-brake so brake the twisted end a copper tube. You running. can get For this this wirepurpose, from companies Omega temperatures canin be monitored while you can such makeas your own Engineering. Reprinted with permission © 1984 Automotive type-K thermocouples by twisting chrome1 andSociety alumel of wire together Engineers, and silver Inc. soldering the twisted end in a copper tube. You can get this wire from companies such as Omega thermocouples must be silverin the lining material close to Inc. the fricEngineering. Reprinted with permission 0 1984 Society of Automotive Engineers,

soldered or crimped into a small Oat thermocouples be springsilverprobe, insulated must and lightly soldered or crimped into a small flat loaded against the rotor friction probe, insulated and lightly springsurface. Brake manufacturers who loaded against the rotor with friction measure rotor temperature rubsurface. Brake manufacturers who make their own; bing thermocouples measure rotor with rubthey are not for temperature sale. bing thermocouples make their A practical alternative used by own; most they are not brake for sale. American and lining manuA practical used by most facturers is to alternative install the thermocouple

American brake and lining manufacturers is to install the thermocouple

tion surface. Temperatures measured

in closelower to the than fricin the thislining way material are slightly tion actualsurface. rotor Temperatures temperature . measured However, in way are slightly lower the this difference is consistent and thethan inactual rotor temperature. However, stallation is much easier and more the difference and the indurable thanis consistent the rotor-rubbing stallation is much easier and more thermocouples. durable than the end rotor-rubbing The thermocouple is stripped thermocouples. back approximately 0.500 in ., twisted , The thermocouple is stripped inserted into a end 3/16-in.-long, back approximately 0.500 in., twisted, inserted into a 3116-in.-long, 111

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SURFACE SHOWN thermocouple for measuring brakeFLUSW WITH Drawing shows bleed-screw fluid temperature. The screw is first drilled through, then twisted thermocouple is bleed-screw silver-soldered in place. Reprinted with permisDrawing shows thermocouple for measuring brakesion © 1984 Society of screw Automotive Engineers, Inc. fluid temperature. The is first drilled through, then twisted

thermocouple is silver-soldered in place. Reprinted with permission 0 1984 Society of Automotive Engineers, Inc.

1/8-in.-OD X 0.086-in.-IO copper tube and silver-soldered in place to 118-in.-OD copper form a plug. XThe0.086-in.-ID plug is installed in tube and silver-soldered in place to the friction material. Typical disc- and form a plug. installations The plug isare installed drum-lining shown in in the friction material. the drawing, page Ill.Typical disc- and drum-lining are shown in If the pluginstallations hole is drilled through the drawing, 11with 1 . a number-31 the lining andpage shoe If the plug hole drilled (O.IOO-inJ drill, theisplug can through be reset the lining andtheshoe withwears a number-31 easily when lining down to (0.100-in.) drill, the plugthermocouple can be reset the plug surface. If the easily when the lining wears to plug is not reset, readings willdown fluctuthe plug surface. If the thermocouple ate between rotor and lining plug is not reset, readings will fluctutemperature. ateThebetween lining drawing atrotor top of and page shows temperature. how to install a thermocouple on a Thescrew drawing at top of page shows bleed for measuring brake-fluid how to installin a athermocouple on a temperature caliper or wheel bleed screw for measuring brake-fluid cylinder. temperature in a caliper or wheel With a mUlti-positio n switch, many cylinder. thermocouples can be connected to a multi-position theWith pyrometer so they switch, can be many read thermocouples When can berunning connected to individually. therthe pyrometer so they can be read mocouple leads from the brakes to the individually. Whento the running chassis, band them flexibletherhymocouple leads from the brakes to the draulic line with plenty of slack so chassis, them to the hythey donband ' t break when the flexible suspension draulic line with plenty of slack so moves. they don't Gage-Brake-tluid break when the suspension Pressure pressure moves. can be measured with a simple presPressure sure gage .Gage-Brake-fluid Marsh Instrument pressure Compacan be measured with simple presny's 14878 gage has lowa displacement sure isgage. Compaand usedMarsh widely.Instrument Another pressure ny's J4878 gageavailable has low displacement gage is also from Hurst and is used widely. Another pressure Performance . gage is also available Hurst used in the A pressure gage can befrom Performance. shop or at the track . If used at the A pressure canthe bedriver used or in obthe track, mount itgage where shop orcan at see the ittrack. usedtheatgage the server easily.If Fill

track, mount it where the driver or observer can see it easily. Fill the gage 112

U-tube decelerometer is made by AM MCO Tools Inc . It's calibratin feet per second per second (ft/sec/sec) rather than g's (1 gI = 32.2 ftlsec/sec) . Instrument reads down Tools scale Inc. for deceleration U-tube decelerometer is made by AMMCO It's calibratandinup scale acceleration. Deceleration scale is used brake (1 g ed feet perfor second per second (ft/sec/sec) rather thanfor g's testing; accelerationlnstrument scale can be useddown for engine and shift= 32.2 ft/sec/sec). reads scale tuning for deceleration pointupdetermination. Instrument can be mounted to windshield and scale for acceleration. Deceleration scale is used for brake with suction cups or scale bolted to be instrument panel. tuning Photo and courtesy testing; acceleration can used for engine shiftAMMCO Tools Inc. point determination. lnstrument can be mounted to windshield Ied

with suction cups or bolted to instrument panel. Photo courtesy AMMCO Tools Inc.

with fluid before mounting it. And always put a valve at the gage so it can with fluid beforenot mounting be shut off when in use andit.soAnd the it can always won't put a valve the gage gage lose at its bleedso when be shut offThe when nottointhe usegage and can so the removed. line be gage won't lose its bleed bled by loosening the valve jamwhen nut removed. The line to the gage can be while applying slight pressure to the bled bypedal. loosening valvebegins jam nut brake Whenthefluid to while applying slight pressure to the leak, retighten the nut to complete brake pedal.. When fluid begins to the bleeding leak, retighten the nut relates to complete pedal Hydraulic pressure the bleeding. effort to actua l force on the brakes. Hydraulic pressure relates pedal When used with a decelerometer, the effort to actual force on pressure gage can be usedtheto brakes. deterWhen used with a decelerometer, mine brake-system effective ness , the or pressure gage can be versus used to vehicle deterto plot pedal effort mine brake-system effectiveness, or deceleration. to plot pedal effort vehicle Camera-Photos are a versus good source of deceleration. test data. Use a camera that provides Camera-Photos are a good of instant prints. Photograp h thesource car just testthe data. Useslams a camera thatbrakes provides as driver on the at a instant prints. Photograph the car prescribed braking point. You mayjust be as the driver slams on the brakes able to detect whether the front or at thea prescribed be rear wheelsbraking lock uppoint. first.You It's may someable detecttowhether thelocks frontuporfirst the timestotough tell which rear wheels lockTouphelp, first.paint It's asomeby observation. large times tough to tell which locks first X on the wheels and tires with up waterby observation. To help, paint a large soluble white paint. X Even on the better wheels and with awaterthantires using still soluble white paint. camera to detect brake lockup is a Evencamera. better It than still video can beusing playeda back camera to detect immediately after brake makinglockup a shot.is Aa video be be played video camera. camera It cancanalso usedback to immediately after making a shot. Aa record instruments in the car during video Tocamera be must used be to stop. do this,can thealso camera record instruments during mounted securely in in the a car bracke t. Aa

stop. To do this, the camera must be mounted securely in a bracket. A

camera is an accura te data recorder-much more so than a person camera is an accurate data reusing his eyes. corder-much more decelerometer so than a person Decelerometer-A is using his for eyes. valuable testing the stopping capaDecelerorneter-A decelerometer is bility of a car. One can be as simple as valuable for testing the stopping capatoppling blocks or as complex as a bility of a car. One can as simple as recording g-meter. See be accompanying toppling blocks as complex and or photos. Buy the as besta illustration recording g-meler. See accompanying decelerometer you can afford. Use the illustration and inphotos. the besta Tapley meter a car Buy in which decelerometer you along can afford. Use the passenger can ride and observe. Tapley in a can car in whichthea Perhaps meter a camera replace passenger ridecare alongto and passenger can if you· rig observe. one up . Perhaps a camera can replace the The Tapley meter indicates actual passenger if you rig one deceleration ratescareasto the car up. is The Tapley meter indicates actual stopping. deceleration the car7350 is AMMCO rates Tools' as model stopping. U-tube decelerometer is easy to install AMMCO Tools' well.model 7350 and adj ust. It works This instruU-tube decelerometer is easy to install ment is used widely by the American and adjust. well. This instruautomob ile Itanworks d brake industries, and ment is used widely by the American many state vehicle-inspection stations automobile in the U.S. and brake industries, and many vehicle-inspection The state simplest decelerometerstations is the in the U.S. toppling blocks. Set up a tray with recThe simplest decelerometer is the tangular blocks as shown. The blocks toppling Seta up a tray recare lined blocks. up along ledge on with the tray. tangulartheblocks as shown. The blocks When car stops, the taller blocks are lined up atalong ledge on the rates tray. topple over lowera deceleration When the car stops, the taller blocks than the shorter ones. Deceleration toppleis over at lower rate between the deceleration tallest block rates that than the shorter ones. Deceleration toppled and the shortes t one that rate is between the tallest block that didn't. toppled andblocks the shortest that Toppling can be one knocked didn't.by bumps or vi brations, so make over

Toppling blocks can be knocked over by bumps or vibrations, so make

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Motion of Car

0.9 x3 - 0.8 0.679 1.339 x2 =-= 0.90g HI 1.5 H1 1.0 H3 0.6 Dimensions of toppling blocks determine maximum deceleration they can take before toppling. Blocks dimensions don't have to be precise as long as they are square. Measure height and width, of each block determine and calculate its toppling deceleration as shown. Each Dimensions of toppling blocks maximum deceleration they can take before block is positioned against adon't thin have ledgetoonbea precise flat trayastolong allow to topple whenMeasure the car toppling. Blocks dimensions as it they are square. decelerates. Tray can be angled toand compensate angle. height and width, of each block calculatefor itsvehicle-dive toppling deceleration as shown. Each block is positioned against a thin ledge on a flat tray to allow it to topple when the car decelerates. Tray can be angled to compensate for vehicle-dive angle.

XI

=-

=

at least three runs to verify the results. If you don ' t get consistent reat least runs definitely to verify work the the brakes sults and three results. If you reeachdon't time,get tryconsistent another test the same sults and the brakes definitely work method. However, be aware that varithe same time, ations in each results cantrybeanother caused test by method. However, be aware that varibrake-temperature changes or other ations in results can be caused by changes. brake-temperature changes or other Tire-Test Instruments-Don't forchanges. get that tire grip affects braking. Thus, Tire-Test Instruments-Don't forto test brakes, also test the tires. You get tiretogrip affectstires braking. Thus, during the maythat wish try other to testbalance the tires. testtest andbrakes, changealso brake to You suit may wish to trytires. otherBring tires during the different along the the test and change brake balance to suit extra tires and instruments needed to the tires. Bring and along the test t1:different em. A tire pyrometer an airextra tiresgage andare instruments needed to the usual minimum pressure test tkem. A tire pyrometer and an airinstruments for tire testing . pressure gage Gages-One are the usuallast minimum instruAir-Pressure instruments for tire ment to consider is testing. a gage for measurAir-Pressure Gages-One last instruing low air pressures in brake-cooling ment to consider is a gage for surfaces air ducts and at the exterior measuring the low car. air pressures in brake-cooling of These pressures are not air ducts and exterior surfaces in inches of measured in at psi,thebut of the (in.Hp). car. These are not water Forpressures comparison, the measured butwater in inches pressure 27inin. psi, below surface of is water (in.H,0). For comparison, the 27 in.Hp, or 1 psi. pressure below water is Gages 27 for in. measuring low surface pressures 27 in.H20, or 1 psi. are very useful for developing brake Gages for measuring low pressures ducts , engine-induction ducts, waterare very usefulairfor developing brake and oil-cooler ducts, driver-cooling ducts, engine-induction ducts, waterducts and even car body-surface and oil-cooler air ducts,manometers driver-cooling aerodynamics. U-tube are ducts and even car body-surface used often for measuring low air aerodynamics. manometers a dial gage is easierare to pressures, but U-tube used often for measuring low air read and install in a car. pressures, but a dial gage is easier to Dwyer Instruments' 2010 Magneread helic and gageinstall readsinupa car. to 10 in. Hp . This Dwyer 2010 small 5-in.Instruments' round gage can be Magnemount10 in. H,O. This helic gage reads up to ed temporarily on an instrument small gage of canthe be steering mountpanel 5-in. or in round the center

ed temporarily on an instrument panel or in the center of the steering

wheel of a cramped formula car. Dwyer also carries all types of wheel of a cramped formula car. manometers.

Dwyer also carries all types of manometers. BRAKE-PERFORMANCE TESTS

There are a few basic-performance TESTS BRAKE-PERFORMANCE much tests that can be made without Thereorare a few basic-performance trouble expensive instruments. All tests can beshould made without brakethat systems deliver much minitrouble or expensive instruments. All mum performance regardless of the brake car type.systems should deliver minimum performance regardless of the To run a basic brake-performance car type. test, pick a distance between stops, To as run0.4a mile, basic or brake-performance such a time between test, pick between stops, one minute. Accelerate stops, suchaasdistance such asrest 0.4atmile, or a time between from wide-open throttle to stops,best suchspeed-to as one minute. your 55 mphAccelerate for a road from wide-open throttlerace to car orrest 80 atmph for a small your best maintain speed-to that 55 mph foruntil a roadit car-and speed car or for 80 the mph a Distance small race is time nextfor stop. or car-and maintain that speed until toit time between stops can be adjusted is time fororthedecrease next stop. Distance or test severi ty. increase time stops firmly can be so adjusted to the brakes the car Applybetween increaserapidly or decrease severity. stops without test locking the Apply the brakes so the car wheels. After the firmly car stops, record stops rapidly without locking the some comments on your data sheet: wheels. carwheels stops,lock? record front the or rear • Did theAfter some on yourordata • Didcomments the car swerve pullsheet: to the Did the front or rear wheels lock? side? Did there the car swerve inor deceleration pull to the a change • Was side? as the car slowed? change in deceleration Was there • Were there anoises from the brakes? as the car slowed? • Was the pedal firm? there noises fromor thewas brakes? stop smooth there • Were Was the the pedal firm? anyWas vibration? Was the stop repeat smooth the or was Immediately test there and any vibration? record your comments. Do this until Immediately repeat the performtest and you notice a change in brake recordoryour this have until ance untilcomments. about tenD ostops you notice a change in brake performbeen completed . It's important to be ance or until ten so stops consistent with about each stop yourhave test

been completed. It's important to be consistent with each stop so your test

Dwyer's 2010 magnehelic gage is easier to install and use than manometer for measuring air pressure. Dwyer's 2010 magnehelic gage is easier

to install and use than manometer for measuring air pressure.

is repeatable for later comparisons. After you finish testing, carefully is repeatable for where later comparisons. touch the wheel it bolts on. After you finish testing, carefully Record the following comments: touch the wheel where it about bolts on. • Are front and rear wheels the Record the following comments: same temperature? rearthe wheels aboutBoth the • Are Can front you and smell brakes? same temperature? sets? youblack smell Both dustthe on brakes? the outside of • Can Is there sets? the wheels? black dust on the outside of • Is Is there grease leaking from the front the wheels? hubs? Is grease leaking from the front The comments you've recorded are hubs? for comparison with other cars or with Thetests. comments recorded beare other There you've are no numbers, for comparison withusing otherinstruments. cars or with cause you are not other tests.you There no numbers, beHowever, canare record your comcause you are not using instruments. ments about specific parts of the However, youperformance. can record your combrake-system The effect ments about specific parts of the of brake-system. changes should be brake-system performance. Thehow effect of learning to recorded as part of brake-system. should be and adjustchanges a brake system. maintain recorded as part ofperformance learning howtest to The overall maintainbeand adjust abybrake system. should followed some work on overall performance test theThe brakes. Usually, there'll be one should be followed by some work on aspect of performance that you wish the brakes. Usually, there'll be one to improve. See the trouble-shooting aspect of performance that12you section following Chapter for wish sugto improve. on See howthe to trouble-shooting correct specific gestions section following Chapter 12 for sugproblems.

gestions on how to correct specific

problems.TESTING TRACK A race car or high-performance TRACK road carTESTING should be track tested . A race car time or high-performance However, the and effort that road car testing shouldat abe goes into tracktrack is nottested. worth However, the timetransportation and effort that car. it for the ordinary goes into testing a track is not worth Performance testsatjust described done it for the ordinary on a country road transportation should suffice.car. In Performance just described done this section, tests I discuss track testing on a country roadtheshould suffice. In aimed at getting highest possible this section, I discuss track testing performance from a brake system.

aimed at getting the highest possible performance from a brake system. 113

Pushrod

Pushrod

Pushrod

Balance-Bar Adjuster Balance-Bar

Measure lining thickness with dial caliper or micrometer before and after each test session determine wear Brake Measure to lining thickness with rate. dial caliper wear can be related toand number stops or or micrometer before afterofeach test laps; particularly important session to determine wear for rate.planning Brake strategy racing. Be sure wear canfor be long-distance related t o number of stops or to measure pads in same place for eachplanning time. laps; particularly important strategy for long-distance racing. Be sure to measure pads in same place each time.

-

Torque Force Wrench Position A Torque Wrench Position A

Torque Wrench Position B

ＮＭ ｾ

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o

.

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I (!)

Ｎ＠

Force Center of Wheel Force Wheel Lug Nut Center of Wheel

w heel Lug Nut To measure torque about wheel center, put torque wrench in position B. Wrench in position A willtorque read about low because distance To measure wheel center, put from wrench to wheel center is B. Wrench in potorque wrench handle in position greater length wrench. Don't sition A than will read low ofbecause distance exceed torque capacity lug nutscenter or bolts. from wrench handle toof wheel is greater than length of wrench. Don't exceed torque capacity of lug nuts or bolts.

Locked wheels is indicated by the smoke. Excessive wheel locking can flat-spot tires, testing Locked making wheels is brake-balance indicated by the smoke. expensive. takes locking a sensitive and Excessive Itwheel can driver flat-spot careful observation to keep from testing ruining tires, making brake-balance tires. expensive. I t takes a sensitive driver and careful observation to keep from ruining tires.

114

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Reference Distance

When making brake-balance changes with a balance bar, make a reference measurement so you know where you started. With this measurement, you can quickly return to your starting balance, if required. changes with a balance bar, make a reference measurement When making brake-balance so you know where you started. With this measurement, you can quickly return t o your starting balance, if required. Recommended track tests are as If you are unfamiliar with the race

follows: Recommendedadjustment. track tests are as • Brake-balance follows: • Deceleration. Brake-balance adjustment. • Effectiveness. Deceleration.measurements. • Temperature Effectiveness.comparisons. • Brake-lining Temperature measurements. Lining Thickness-Before you start Brake-lining testing, check comparisons. brake lining thickness. Lining Thickness-Before you their start Remove the linings and measure testing, check brake lining thickness. thicknesses with a micrometer. It's Remove the alinings andcaliper. measure their OK to use vernier Record thicknesses a micrometer. It's each lining with thickness on your data OK to use a vernier caliper. Record sheets. Also indicate where on the each lining thickness onwasyour data lining each measurement taken. sheets. Also indicate where on so Disc-brake pads wear on a taper,the lining eachthem measurement was taken. measure in the middle and at Disc-brake pads wear on a taper,linso each corner. Measure drum-brake measure them in the middle and at ings at each corner and at the inside each corner. Measure drum-brake linand outside edges of the center. Measings the at each corner and at the of inside ure combined thickness the and outside edges of the center. Measlining and shoe plate. Subtract shoeure the combined of the plate thickness to get thickness lining thickness. lining and shoe plate. Subtract shoeThe purpose of these measuremen ts plate thickness get lining is to check for to lining wear. thickness. By recordof these measurements ingThe thepurpose total number of hard stops is to check for wear. By recordduring testing, lining you can calculate the ing the total number of hard amount of wear per stop. Youstops can during testing, about you can calculate the then calculate how long your amount of wear per stop. You can brake linings will last. then aboutthehow longareyour Brakecalculate Balance-If linings not brake linings will last. bedded in, do it before testing. This Brakealso Balance-If are and not will warm upthe thelinings engine bedded in, do it before testing. This chassis. Check page 40 for details will also upbrakes. the engine and about how warm to bed in chassis. Check page for car, details If you are testing 40 a race it about how bedadjustable in brakes.balance bar. should havetoan a race car, init you are A Ifbalance bar testing is usually mounted should have an adjustable balance bar. the pedal and is adjusted from one A balance bar is ausually mounted in end by loosening jam nut and turnthe the pedal and aisscrewdriver. adjusted from one ing bar with

end by loosening a jam nut and turning the bar with a screwdriver.

car, you may not know where to set you are bar. unfamiliar with the theIf balance Start setting it at race the car, you may not know where to seta center of its adjustment and perform the balance bar. Starttest. setting at the simple brake-torque Jackit up the center of its adjustment and perform car and put it on jack stands so thea simple brake-torque Jack upHave the tires are off the test. ground. car and put it on jack stands so the someone sit in the car and lightly tires are off the With ground. Have the brakes. the helper apply someone sit in the car and lightly holding the brake pedal, turn a front, apply helper then athe rearbrakes. wheel With usingthe a torque holding the brake pedal, turn a front, wrench on a lug nut as shown in the then a rear wheel usingRecord a torque accompanying drawing. the wrench a lugcan't nut asmeasure shown in the results. on If you brake accompanying drawing. Record the torque with a torque wrench, use your If you can't measure brake results. hands and estimate it. torque wrench,torque use your Start with witha torque front-brake at hands and estimate it. about 50% greater than rear-brake Start ifwith front-brake torque at torque, the car has 50-60% of its about 50% greater than rear-brake weight on the rear wheels. If the car is torque, if the car has 50-60% of its extremely nose-heavy, set front-brake weight the rear wheels. the car is torque on at about 100% moreIfthan rearextremely nose-heavy, set front-brake brake torque. But if it is extremely tailtorque at about than rearheavy, start with100% front-more and rear-brake brake torque. But if it is extremely tailtorques approximately equal. This heavy, start with frontand rear-brake also confirms that both front- and torques approximately rear-brake systems work. equal. This also confirms that both isfrontand If front-brake torque less than rear-brake work. rear, adjustsystems the balance bar. is less than If front-brake The tricky part torque of balance testing is rear, adjust the balance bar. figuring out which end locks up first. The tricky part ofhelpers balancetotesting is You'll need some do this. figuring out which end locks up first. As suggested, this is the time to use a You'll need or some helpers to With do this. still camera video camera. an As suggested, this is the time to use instant-replay video camera, you cana still camera or video With an observe at leisure whatcamera. happened. instant-replay can A driver willvideo have camera, difficultyyou telling observeend at leisure what happened. which of a car locks up without A driver will telling flat-spotting the have tires. difficulty Instead, he has which end of a car locks up without to ease off the pedal the moment a flat-spotting thelock tires. he has wheel starts to up.Instead, If he doesn't,

to ease off the pedal the moment a wheel starts to lock up. If h e doesn't,

White spot on tire is cord showing through where rubber was worn off. Locking brakesspot risks tires and also White on flat-spotting tire is cord showing through going through cord.worn Tire is and where rubber towas off.ruined Locking must be risks replaced. brakes flat-spotting tires and also

going through to cord. Tire is ruined and must be replaced.

he can grind right through the tires. Flat spots can ruin a tire. Be careful! heDo canthe grind through thetest tires. firstright brake-balance at Flat spots can ruin a tire. Be careful! moderate speed-about 40 mph . If DO test to at you gothe too first fast, brake-balance the car will be hard moderate speed-about observe safely. If yo u're 40 not mph. using Ifa you too fast,position the car people will be on hard to both videogocamera, observe safely. If you're not using sides of the track. Use two observersa video camera, on both on each side ifposition possible.people Tell them to sides of the twoorobservers try and see track. if the Use front the rear on eachlock sideupif first. possible. them to Don Tell 't lock up all wheels try and see if the front or the rear four wheels. The test will then mean wheels up first. Don't lock up all nothing,lock so don't brake too hard. four wheels. test lock will first, then adjust mean If the frontThe wheels nothing, so don't brake too hard. the balance for more braking. Make If the lock first, sure youfront turn wheels the adjuster in theadjust corthe forRecord more braking. Make rect balance direction! the number of sure adjuster the data corturnsyou on turn the the adjuster in in your rect direction! Record the number of sheet and retest. Continue testing turns on the adjuster in your data until you are satisfied with brake sheet balance.and retest. Continue testing until are wheels satisfied should with brake The you front lock balance. before the rears. Rear-wheel locking The instability. front wheels should lock causes If the car is turning before Rear-wheel or has the any rears. side forces on it, locking it will causesFront-wheel instability. If locking the car iscauses turninga spin. or has any side forces on it, it will car loss of steering control, but the spin. Front-wheel locking causes usually goes in a straight line. Thea loss of steering control,onbut final setting will depend the the typecar of usually goes in 's a preference. line, l-he car and the driver final setting the type of If your carwill has depend wings oronaerodynamcar and the driver's preference. ic downforce from ground effects, If your car has or aerodynambrake balance maywings be different at high ic downforce effects, rear speeds. A rearfrom wing ground loads the brake balance mayincreases. be different Onatahigh car wheels as speed A rear wing loads thebrakes rear speeds. that has only a rear wing, if the wheels as speed increases. On a the car are evenly balanced at 40 mph, that has only will a rear wing, front wheels lock first ifatthe 100brakes mph. areis evenly balanced at 40 the mph, the impossible to balance brakes It 100 mph. front wheels will lock first at for all speeds on such a car. It is impossible Compromise . to balance the brakes forRace-car all speeds such more a car. brakes on are used at Compromise. high speed than at low speed. The Race-carbraking brakes speed are used more at minimum on the track high speed at lowturn. speed. is going into than the slowest PickThe an

minimum braking speed on the track is going into the slowest turn. Pick an

rear of sports racer improves rear-tire traction for improved handling and braking IatWinghighat speed. -*. As speed drops, so does wing downforce, increasing the chance of rear.-

I

wheelat lockup when braking tight corners. -.id braking Wing rear of sports racerfor improves rear-tire traction f-. ....,. at high speed. As speed drops, so does wing downforce, increasing the chance of rearwheel lockup when braking for tight corners.

Ground effects and rear wing provide maximum aerodynamic downforce. Wing also increases drag dramatically. NACA ducts optimize airflow to brakes with minimum drag.

Ground effects and rear wing provide maximum aerodynamic downforce. Wing also increases drag dramatically. NACA ducts optimize airflow to brakes with minimum drag.

average braking speed for the particUlar track and set the balance for that average speedstrongly for the particuspeed . Ifbraking the driver prefers lar track set theover balance for that one type and of balance another, the speed. thebedriver strongly prefers brakes If may balanced perfectly at one type of over another, the top speed andbalance increasingly unbalanced brakes perfectly at speedmay dropsbe. Abalanced lot of experimenting as top speed and increasingly is needed to arrive at unbalanced the best as speed drops. compromise . A lot of experimenting is Remember needed tothatarrive the isbest bra ke at balance afcompromise. fected by the foJ]owing: Remember that brake balance is afchanges-could be caused • Tire-grip fected by the following: by either track-surface changes or tireTire-grip changes-could be caused temperature changes. by either track-surface changes tire• Aerodynamic-force changes,or such

temperature changes. Aerodynamic-force changes, such

as a wing-angle change. temperature-fade may • Brake as a wing-angle change. at one end of the car before the occur Brake may other end . temperature-fade occur at one end of the car before the • Change to different-size or -comother end. pound tire. Change to to different-hardness different-size or -cornbrake • Change pound tire. lining. Change toto different-hardness brake the car weight distri• Change lining. bution. Change intomaster-cylinder the car weight size.distri• Change bution. Because it is difficult for a driver to Change in master-cylinder detect small brake-balance size. changes, Because it is difficult for a driver to don ' t be concerned about small detect small However, brake-balance adjustments. if youchanges, make a

don't be concerned about small adjustments. However, if you make a 115

Severe changes in track conditions is why brake balance needs to be adjusted by the driver. If Geoff Lee's Formula Ford was set up for the dry, front wheels would lock in the wet. To changes correct, in balance is is changed to give more needs rear-wheel and Severe track adjuster conditions why brake balance to bebraking adjusted by less the front. During testing, can deliberately wet to find correct rain settings. driver. If Geoff Lee's you Formula Ford was set upthe fortrack the dry, front wheels would lock Photo in the by Steven Schnabel. wet. To correct, balance adjuster is changed to give more rear-wheel braking and less

front. During testing, you can deliberately wet the track to find correct rain settings. Photo by Steven Schnabel.

ｾａ＠

1.0

A

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0.81--====::::::-=---

0.8 Average Deceleration

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-

(g) Average Deceleration

A.

(g)

o

40

80

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B

yc 120 I

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---- B

I I Speed When Brakes Are Applied (mph)

40

I

80

120

balance-bar, master-cylinder valve problems later.TESTS DECELERATION

160

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problems-it has lift at high speed. Most road cars have less deceleration at higher speeds, but not as severe as curve B shows.

only a few laps, make only one and then discuss with the ob-

change, 116

and

A verage Deceleration - This test is

I I

160

Average deceleration tests will tell you When something about car's aerodynamic downforce. If Speed Brakes Are aApplied (rnph) deceleration increases with higher-speed stops, stopping is improved with downforce, asI I shown bydeceleration curve A. Curve B will reflects a car with littleabout or noadownforce. Curve Cdownforce. is a car with Average tests tell YOU something car's aerodynamic If problems-it has lift at high Most road cars have lessisdeceleration at higher speeds, deceleration increases withspeed. higher-speed stops,-stopping improved with downforce, as but not by as curve severeA.asCurve curve BB reflects shows. a car with little or no downforce. Curve C is a car with shown

big adjustment, brake balance should be checked by testing. The most imbig adjustment, balance should portant factor is brake tire grip, caused by be checked by testing. The most either changing track conditions orimby portant tire grip, by the tires.factor Tiresis often lose caused grip with either changing track conditions by age , wear or temperature change.orTest the tires. Tires often lose grip with the car with the setup you will be runage, temperature change. Test ning wear in theorrace. theIfcar with you will be runyour carthe hassetup a cockpit-adjustable ning in the balance bar,race. check it during a test sesIf your has aThe cockpit-adjustable sion at thecartrack. driver should balance bar, check it during seschange balance to see howa test it feels. sion the track.should The driver Also, atobservers recordshould what change see braking. how it feels. happens balance during tohard Run Also, observers should only a few laps, makerecord only what one happens and during change, then hard discussbraking. with theRun ob-

deceleration. Remember, as deceleration increases, so must front-wheel deceleration. Remember, as decelerabraking. tion increases, must front-wheel If your car has so well-balanced brakes braking. and you want to change a master cylinyour cara has well-balanced brakes derIf or go to different type of proporand you valve, want tothis change tioning can abemaster done cylinwithder or go to a different of proporout changing balance. type However, you tioning valve, this be pressure done withmust measure and can record in out you bothchanging hydraulicbalance. circuits However, before changmust measure and be record in ing parts. This can donepressure by installboth hydraulic circuits before changing pressure gages downstream from ing This can be doneand by proporinstallthe parts. front master cylinder ing pressure from or downstream the rear master tioning valvegages the front Amaster cylinderplace and isproporcylinder. convenient at the tioningandvalve or thebleed rearscrews. master frontrear-caliper cylinder. A convenient place is at the by Modify two spare bleed screws frontand rear-caliper bleed screws. brazing the cross-hole shut, drilling Modifythe twocenter spare hole bleedand screws by through brazing brazing the cross-hole shut, drilling an adapter fitting to the end of the through the center hole and brazing screw . Install one modified screw in a an adapter to inthea rear end caliper. of the front caliperfitting and one screw. Install one modified in a Connect a gage to each screw modified front caliper and one in a rear caliper. screw with flexible brake hose or steel Connect a gage modified tubing and bleed to theeach gages. While screw withapplies flexible the brakepedal hose to or steel someone give tubing and the gages. 800-psi frontbleed pressure, read theWhile rear someone pedalmake to give pressure . applies You canthenow the 800-psi front pressure, rear system changes. Withread thethegages pressure. You can make the now balance bar the or installed, adjust system changes. theandgages proportioning valve With so front rear installed, read adjustthethe balance bar the or pressures same as before proportioning valve so front and rear change. Be sure to keep this gagepressures read the same before itthe and-bleeder-screw setup as because is change. Be sure keepsorting this gagean excellent toolto for out and-bleeder-screw setup because itand is balance-bar, master-cylinder an excellent tool for sorting out valve problems later.

servers what they saw. If you make more than one change before testing, servers whatbe they If you make won't able saw. to pinpoint what you more than one change before change to the brake system testing, caused you be able change to pinpoint what whichwon't observable in brake change to the brake system caused performance. which brakea If theobservable track surfacechange is dirty in or wet, performance. balance test will be useless unless you If the dirty orsurface. wet, a plan to track race surface on a is similar balance test willa be useless unless Instead, make crude attempt at you setplan to raceif on similar surface. ting balance the abrakes were never Instead, make a crude deceleration attempt at setset. Record maximum so ting if the never you balance can judge howbrakes muchwere to change set. deceleration so the Record balance maximum when traction improves. you can judge how much to change After a few brake-balance tests, you'll the balance when balance traction settings improves. be able to relate to

After a few brake-balance tests, you'll be able to relate balance settings to

DECELERATION used to determine TESTS how rapidly a car Average is stops. TheDeceleration-This test can be done withtest miniused to determine how rapidly a car mum effort using a stopwatch. If you stops. test can be done withtominiknow The the time it takes a car stop mum effort using a speed, stopwatch. If you calculate from a known know the time it takes a car to stop deceleration: from a known speed, calculate Average deceleration = :2t in g's deceleration: Average deceleration = stop in g's S = Car speed in miles before the

&

per hour S Car speed theinstop in miles t ==Time it takesbefore to stop seconds

per hour do itthis testtoyou know the t =ToTime takes stopmust in seconds speed of the car. If the car has a To do this test youthemust know the speedometer, have speedometer speed of the car. If the car has a calibrated at a speedometer-repair speedometer, the speedometer shop. If there ishave no speedometer, have calibrated at ashop speedometer-repair a speedometer put the car on shop. there is no speedometer, have machine, their Ifspeedometer-testing aandspeedometer shop put the car on record the miles per hour that cortheir speedometer-testing machine, respond to various tachometer and recordMake the miles hour that correadings. sureper you record the respond to various tachometer gear ratio , driving-wheel tire size and readings. record the what gear Make the carsure is inyou when making gear ratio, driving-wheel tire size and what gear the car is in when making

this test. Speedometer and tachometer calibrations are necessary because this Speedometer tachometer they test. usually read in and error, causing calibrations are necessary because errors in calculations. they usually read in error, When stopping from verycausing high errors indeceleration calculations. changes during speed, stopping from high theWhen stop. Therefore, averagevery deceleraspeed, deceleration changes during tion must be compared to other stopthe decelerapingstop. tests Therefore, done at the average same speed. tion must be compared to other stopit Bring the car up to speed and hold ping tests done at the same speed. steady. Start the stopwatch the instant theare carapplied; up to speed it theBring brakes stopand the hold watch steady. Startthe thecar stopwatch the instant the instant stops. Timing can the brakes applied; in stop be done by are a passenger thethe carwatch or by the instant the car stops. Timing an observer. Several tests should can be be done by a passenger in the by run to minimize errors, butcar letorthe an observer. Several tests. tests should be brakes cool between If you are run to minimize but leteach the getting about the errors, same results brakes cool between tests. If you are. time, your testing methods are good getting about the same results each However, it's difficult to do this test time, your testing methods are good. be surprised if accurately, so don't However, it'sconsistent difficult to do this test you can't get results. accurately, don't begin be surprised if your stops To reducesoerror, you can't get consistent results. from a higher speed. Start the stop To reduce error, begin reaches your stops watch as the speedometer the from a speed. higher Ifspeed. Start observer the stop a trackside desired watch as the speedometer the is timing, you'll need to reaches signal him desired speed. If a trackside observer when to start timing. is It's timing, you'll toneed to signal him interesting measure the averwhendeceleration to start timing. when braking from age It's interesting measure avervarious speeds. Iftoyour test the methods age deceleration when braking from are consistent, you can plot a graph of various speeds. If your methods deceleration versus car test speed. This are you can plot aof graph of will consistent, indicate the amount aerodeceleration versus car speed. This dynamic downforce . If average decelwill indicate the amount of aeroeration increases with stops from dynamic downforce. If average decelhigher speeds, the car has increasing eration increases stops downforce at higher with speeds. Mostfrom cars higher speeds, the car has increasing have less deceleration at high speed downforce higher The speeds. Mostrotatcars for several at reasons. wheels have deceleration high speed ing atless high speed takeat away some for several reasons. Thethe wheels rotatdeceleration the instant driver hits ing at high speed take away the brake pedal. Also, many cars some have deceleration the the driver aerodynamic liftinstant at high speed, hits so the Also, . many cars have theybrake have pedal. less traction aerodynamic lift at highdeceleration speed, so While performing they have less traction. tests, also measure stopping distance performing forWhile each speed . Providingdeceleration you know tests, alsoand measure stopping distance car speed stopping distance, decelfor each speed. Providing you know eration can be calculated from the folcar speed and stopping distance, decellowing formula:

eration can be calculated from the folS2., · lowing formula: A d I t verage ece era Ion

=

29.9d

In

9s

a S2

Average deceleration = in g's S = Car speed before the stop in miles per hour S = Distance Car speedit before theto stop ininmiles takes car stop feet d= per hour Distance takes harder car to stop feet d= This test is itmuch thaninusing

a stopwatch because it's difficult to hit testatis amuch harder using theThis brakes certain spot. than Observers a stopwatch becausethat it's braking difficult really to hit can help confirm the brakes a certain Observers starts whereatthe driver spot. intends.

can help confirm that braking really starts where the driver intends.

Toppling Block

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wedge

M

Floor

Forward Direction

Forward Direction

To compensate for nosedive during a toppling-block test, first photograph car from the side hard braking. From photo, measure dive angle A of car as shown. Make a wedge atI this angle and place it under during toppling block tray. Usetest, a protractor/level to car check tray To compensate for nosedive a toppling-block first photograph from theangle side in car. hard braking. From photo, measure dive angle A of car as shown. Make a wedge at during

Iduring

this angle and place it under toppling block tray. Use a protractor/level to check tray angle in car.

Again, accelerate the car to a constant speed and make several practice Again, accelerate the car a contests. If you do both time andtodistance stant speed andon make practice measurements eachseveral test, compare tests. If you If doyou bothmeasured time and the distance the results. time measurements on each test, compare and the distance accurately, you the results. you same measured the time should get If the deceleration and distance methods. accurately, using the the different On you the should get errors the same deceleration other hand, in measuring will using inconsistent the different methods. On the give results. Because other hand, errors in measuring will speed is squared in the stoppinggive inconsistent Because distance formula, theresults. speed measurespeed squared in the stoppingment is is critical. distance formula, the speed If you are having troublemeasuregetting is critical. ment accurate deceleration measurements, youMark are ahaving tryIfthis: line ontrouble the roadgetting or set accurate deceleration measurements, up markers where braking should try this:Start Markthe a line on the road or car set begin. stopwatch as the up markers where braking should crosses the line. To apply the brakes begin. Start theline, stopwatch as the car approach it with exactly at the crosses theoff line. apply the your foot theTothrottle andbrakes posiexactly at the approachpad. it This with tioned over theline, brake-pedal your foot off the throttle and posireduces driver-reaction time. It takes tioned 1/2 oversecond the brake-pedal pad. This about to move your foot reduces time.pedal. It takes from the driver-reaction throttle to the brake about second to read movethe your foot Have112 a passenger speedfrom the throttle to the brake pedal. ometer or tach. It may be necessary to Have a passenger read the the instrument for speedeasier reposition ometer It may to reading. orOr,tach. if you havebea necessary camera that reposition the instrument for easier can be tripped electrically - necessary reading. Or, if you have a camera with a single-seater-you could that use can tripped electrically the be brakelight switch to-necessary trip the with a and single-seater-you could use camera take a photo of the speedthe brakelight switch to trip ometer the moment the brake pedalthe is camera and take a photo of the speedhit. ometer thethe moment brake pedalthe is To get speed the right when hit. brakes are applied, run some tests

To get the speed right when the brakes are applied, run some tests

without hitting the brakes. Back off the throttle at a mark on the road without hitting the the line brakes. off and Back observe before crossing the throttle at a mark on the road the speed as you cross the line. Adjust before crossing the line so you crossand theobserve line at initial speed the speed as you cross the line. Adjust the desired speed. initial speed so youto cross line of at If you are going run a the number the desired speed. deceleration tests, you should invest you are going to run a number of in If a decelerometer. deceleration tests, you should invest Maximum Deceleration Tests-You in a decelerometer. can measure maximum deceleration Maximum Deceleration You can alsoTests-You test decelduring a stop. can measure maximum deceleration eration at particular speeds without during a stop. test decelstopping. To doYou this,can usealso a deceleromeration at particular eter or toppling b10cks.speeds without stopping. To do use athe deceleromDecelerometer-this, Follow instruceter toppling tionsorthat comeblocks. with the instrument. Decelerometer-Follow the a instrucMost decelerometers require passentions that come with the ger to take readings . On ainstrument. single-seat Most require a passenracer, decelerometers this is not practical. Instead, use ger to take readings. On ainsingle-seat a video camera mounted the car to racer, is not practical. Instead, use recordthis decelerometer readings. aToppling video camera mounted in the car to Blocks-The toppling-block record decelerometer readings. method doesn't require a passenger. Toppling Blocks-The blocks-see toppling-block drawing-can Toppling method doesn't require a passenger. be built in a home workshop. Make a Toppling blocks-see drawing -canA flat surface for the blocks to rest on. be built in a can home Makeina be workshop. mounted firmly flat tray that flat the blocks restthe on.car A yoursurface car is for ideal. Don't to use flat tray that can be mounted firmly in floor. Chances are it's not flat enough youraccurate car is measurements. ideal. Don't use the car for floor. are it's gradually not flat enough Set Chances up the blocks, bring for the accurate car up tomeasurements. speed and hit the brakes. Set upwillthe blocks, bring You topple gradually the blocks the car up to speed and hit the brakes. immediately, so you don't have to You will speed. toppleWiththe blocks lose much the blocks, immediately, so you ordon't to you'll find maximum peak have deceler-

lose much speed. With the blocks, you'll find maximum or peak deceler117

Temperature-indicating paint is best way to measure rotor temperatures. Paint can be applied to outer edgepaint of rotor and way obTemperature-indicating is best served after rotor test run. ExperimentPaint with difto measure temperatures. can ferent temperature to rotor get good be applied to outerranges edge of and test obdata. an test open-wheel car, a pyrometer servedOn after run. Experiment with difcan be temperature used, but youranges must act fastgood to avoid ferent to get test having rotor off before data. On an cool open-wheel car,measurement a pyrometer is taken. can be used, but you must act fast to avoid

having rotor cool off before measurement is taken.

ation during that range of speed when the brakes were applied . By running a ation during that, you rangecan of plot speed when number of tests a graph the brakes were applied. By running of deceleration versus car speed.a number of tests, can plot graph Again, this is an you indication of avehicle of deceleration versus car speed. If deceleration is higher at downforce. is an aerodynamic indication of vehicle Again, higher this speeds, downdownforce. If deceleration is higher at force is present and vice versa. higher speeds, aerodynamic downEach block falls over at a certain force is present vice versa. deceleration . Mand aximum deceleration Each a block fallsbeover at a certain during stop will indicated by the deceleration. Maximum deceleration shortest block that fell over. The during acan stop tell will be indicated bywhat the driver immediately shortest block that fell by over. The deceleration he is getting looking driver can tell immediately what the blocks. at deceleration he iserror getting lookingThere is some in thebytoppling at the blocks. block test. If the car nosedives while There isthe some errorwill in the topplingblocks tend to fall stopping, block the car nosedives while more test. easilyIf than if the car stopped stopping, the blocks will tend to fall level. Most race cars don't nosedive more easily than if the car stopped enough to matter, but the error may level. Most race don't nosedive on cars a high-CG, softly be significant enough to matter, but the error may sprung road car. beTosignificant on for a nosedive, high-CG, take softlya compensate sprung road car. photo of the car from the side while it compensate for nosedive, take a is To stopping at maximum deceleration. photo car from the side while of it thethe photo, measure the angle Using of is stopping at maximum deceleration. tilt of the body. Compare it to a photo Using the photo, measure of taken from the same anglethe ofangle the car tilt of the body. Compare it to angle a photo Once the dive is sitting level. taken from , the samethe angle the the car determined adjust trayof for sitting Once dive up angle is topplinglevel. blocks. Tip the the tray at the determined, adjust the tray for the front , at the same angle the car toppling blocks. tray up at the nosedives. This Tip willthe compensate for front, at caused the same angle theOncara the error by nosediving. nosedives. Thisnosedive, will compensate for car with little position the the error caused by nosediving. On toppling-block tray level on the cara car with little nosedive, position the floor.

toppling-block tray level on the car floor. 118

Check Changes-When making deceleration tests , now's the time to Check making deceleration is affected by check howChanges-When deceleration tests, now's the time to changes other than to the brakes. For check how deceleration is affected by example, you can combine the decelchanges other than to the brakes. eration test with aerodynamic testsFor to example, can combine decel-. see how you downforce affectsthe braking eration test this with aerodynamic tests to Combine with brake-balance see how downforce affects braking. changes to achieve maximum Combine with brake-balance deceleration.thisRemember, maximum changes achieve maximum decelerationto occurs when brake baldeceleration. maximum ance is set soRemember, all four wheels lock deceleration occurs when brake balsimultaneously. ance is set so wheels Although tire all gripfour is the most lock imsimultaneously. portant item affecting deceleration , it tirebygrip is theinmost imis Although also affected a grade the road portant item affecting deceleration, it or the wind. So test in both directions is also affectedthebyresults a gradetoineliminate the road and average or the effects. wind. So in bothday, directions these Ontest a windy a large and average the results to eliminate error is introduced . Wind forces vary these a windy day, a On largea the effects. square On of the wind speed. as error isday, introduced. Wind will forces vary change windy drag forces as the squaresignificantly. of the wind speed. On a deceleration

windy day, drag forces will change deceleration significantly. EFFECTIVENESS TESTS

Brake-system effectiveness is the EFFECTIVENESS TESTS amount of deceleration obtained for a Brake-system effectiveness the particular pedal effort. A isbrake amount of deceleration obtained for system that is more effective stops aa particular effort. A brake car with less pedal pedal effort. system that is more stopsfora Effectiveness testseffective are useful car with less pedal effort. comparing brake systems and also for Effectiveness tests are tests usefulmust for comparing linings. These comparing brakea systems and also for be run with continuous-reading comparing linings. tests must decelerometer, suchThese as aU-tube debe run with a continuous-reading celerometer or reco rding g-meter and such With as a U-tube deadecelerometer, line-pressure gage. a recording celerometer or tests recording g-meter, these can beg-meter run by and the adriver line-pressure With aa recording alone. gage. With U-tube g-meter, these tests be run by the decelerometer, ancan observer is driver alone. With a U-tube required. decelerometer, an observer is To run an effectiveness test, dri ve required. the car at a predetermined speedTo as run60an effectiveness drive such mphand applytest, the brake the car at a predetermined speedpedal until a 100-psi pressure is such as 60 the brake reached. Atmph-and that point ,apply deceleration is pedal and untilrecorded. a 100-psi is read Thenpressure accelerate reached. At that is the car back to 60point, mph deceleration and repea t the read and recorded. Then accelerate test in increasing 100- or 200-psi the car backuntil to 60lockup mph and repeat the increments is reached. Be test to in allow increasing 100-time or between 200-psi sure sufficient increments lockupfor is reached. Be each pedal until application the brakes sure to allow sufficient time between to cool. each pedal application for the brakes Following each test , calculate pedal to cool.required for each pressure . Plot effort Following each paper test, calculate pedal with decelerathis data on graph effort required for each pressure. tion in g's on the vertical axis Plot and this on graph paper with deceleraon the horizontal axis. pedaldata effort tion in g's comparison, on the vertical axis and For easy if you test pedal effort thedifferent horizontal axis. another car oronwith lining on For easy car, comparison, if you the same plot the second testtest on another or with lining on the samecar graph. Fordifferent a quick comparithe same plot, the on son and nocar, graphs run second the teststest at just

the same graph. For a quick comparison and no graphs, run the tests at just

Effect of scoop on brake temperature can be tested by enlarging scoop. If you make scoop larger andontemperature drops, use Effect of scoop brake temperature can this information to design improved be tested by enlarging scoop.anIf you make scoop. larger Use theand smallest scoops drops, to give use acscoop temperature ceptable brake temperatures because big this information to design an improved scoops increase air drag.scoops to give acscoop. Use the smallest

ceptable brake temperatures because big scoops increase air drag.

one line pressure decelerations.

and

compare

one line pressure and compare decelerations. BRAKE TEMPERATURE TESTS Brake temperature is important to

BRAKE the brakes get TESTS too hot, know . IfTEMPERATURE Brake temperature is important to cha nges may be necessary. By measurknow. the brakes get can too check hot, ing the Iftemperature , you changes mayofbeanecessary. By ally, measurthe success ch ange. Usu iming the temperature, you can check proved airflow to the brakes will be the most success of a change. the effective change. Usually, improved airflow to temperature the brakes will Measure brake withbea the most effective change. hand-held or remote pyrometer. You brake temperature with a temperature-indicating canMeasure also use hand-held or remote paint or labels. The pyrometer. hand-held You pycan also gives use the temperature-indicating rometer temperature at the paint The hand-held The pytime or of labels. the . measurement. rometer gives the temperature at the remote pyrometer with thermocoutime gives of the 'measurement. ples continuous temperatuThe res. remote pyrometer with give thermocouTemperature indicators maxiples gives continuous temperatures. mum temperature experienced at a Temperature indicators give maxispecific location. m uThe m disadvantage temperature of experienced a hand- heldatpy-a specific rometerlocation. is it takes time to stop the of aand hand-held pycar,The getdisadvantage to the brake, make the rometer is it takes time to stop the measurement. By that time, temperacar, to the brake, and make the turesgethave dropped . Therefore, the By that time, temperameasurement. hand-held pyrometer will be useful tures ifhave dropped. Therefore, only you can get fast access to the the hand-held pyrometer will useful spot to be measured . For be example, only if you get fast race access to but the it'll work on can open-wheel cars, spot to beimpossible measured.on For example, is almost full-fendered it'll work on open-wheel cars, but cars that don't have largerace openings in is almost impossible on full-fendered the wheels. cars that are don'tmany haveways largetoopenings in There determine the wheels. Whatever you do, plan temperature. are and many waysthetowritten determine theThere test first follow plan. temperature. Whatever you You must have good recordsdo,to plan get the firstinformation. and follow theIt written plan. doesn't do any test useful You must have good records to get any useful information. It doesn't do

any good to say, "My brakes get to lOOOF." You must know how many any good say, "My get to stops weretomade, from brakes what speed, 1000F." how many and how You muchmust time know elapsed between stopsstop. wereAlso, made, from speed, each a car thatwhat sits still beand how much elapsed than between tween stops is a time lot different if it each stop. Also, a car thatfor sitsthe still bewas moving at 100 mph same tween stops is a lot different than if it time period. was at 100 same If moving you don ' t mph have fora theremote time period. pyrometer, use the next best If you don't have aindicators remote thing-apply temperature pyrometer, the and nextlabelbest to your brakes.use The paint inthing-apply dicators go on temperature the edges of indicators the brake to yourand brakes. Thebody, paint respectively. and label inrotor caliper dicators on temperature the edges of gets the brake Usually, go rotor twice rotor and caliper body, respectively. that of the caliper. Usually, rotor temperature gets twice Accelerate to a predetermined that ofand the caliper. speed make one full stop. Check a predetermined theAccelerate temperaturetoindicators and record speed and make one full temperature. stop. Check the maximum-indicated theyou temperature indicatorsasand record If have a pyrometer well, use theTemperature maximum-indicated temperature. it. rise in one stop can If have a topyrometer as well, use be you compared a calculated number it. Temperature rise in one stop can using the formula on page 11. The difbe compared to a calculated number ference between calculated-tempusing therise formula on measured page 11. The erature and the risedifis ference between calculated-tempthe energy-heat-Iost elsewhere, erature and caliper, the measured is such as rise to the wheel, rise brake the energyheat-lost elsewhere, hats and air drag. such as to thea caliper, wheel, If you have road-racing car, brake make hats and air drag. a number of fast laps around the track you have a road-racing at Ifracing speed. After aboutcar, 10 make laps, abring number the brake track the of carfast in laps and around measure at racing speed. Afterthis about 10 laps, laps, temperature. After many bring the car in and measure brake brake temperature should stabilize. temperature. many laps, To check this, After make this several multilap brake temperature should after stabilize. tests, checking temperature each To this,Eventually, make several multilap set check of laps. you'll find tests, checking temperature after each how many laps it takes for the brakes set laps. maximum Eventually,temperature. you'll find to of reach how many laps get it takes the brakes They will not any for hotter unless to reach maximum temperature. there's a major track , car or driver They nota get any pyrometer hotter unless change.will With remote and there's a major linings, track, car driver thermocoupled thisorcan be change. With a remote and done easily in one seriespyrometer of laps. thermocoupled be Pay particular linings, attentionthisto can caliper done easily innear one series of laps. temperature the piston (s). If the Pay particular to caliper temperature gets attention close to the braketemperature near the piston(s). fluid dry boiling point, watchIf the for temperature gets close to theatbraketrouble. A caliper running over fluid dry boiling point, watch for. SOOF (260C) will experience trouble trouble. caliper running at ifover The sealsAeventually leak even the 500F doesn't (260C) boil. will experience trouble. fluid So try to limit caliThe seals eventually leak even if the per temperature to 3S0F (177C) or fluid doesn't boil. So less, to give longer sealtry life.to limit caliperTotemperature to 350F (177C) or evaluate differences between less, to give longer seal life. different components or setups, such evaluate as Tocool ing-duct differences systems orbetween rotor different setups, such types, it iscomponents best to test or one configuraas or right. rotor tion cooling-duct on the left andsystems one on the types,, switch it is best to and test rerun one configuraThen sides the test. tion on the left and one the right. Caution: When runningontests with Then, switch sidesonandeach rerun theoftest. different setups side the

Caution: When running tests with different setups on each side of t h e

Temperature-indicating labels are for use on disc-brake calipers. Note the word CAUTION starting at 320F (160C). Temperature-indicating labels are forTemuse perature indicates fluid may on disc-brake calipers. Note be the boiling word inside caliper. Photoatcourtesy AP Racing. CAUTION starting 320F (160C). Tern-

perature indicates fluid may be boiling inside caliper. Photo courtesy AP Racing.

.'" ,

Temperature-indicating paint at different locations on caliper : Paint on outboardpiston housing is most important because Temperature-indicating paint at different it indicateson fluid temperature cooling locations caliper: Paint where on outboardair is minimal. not because exceed piston housing Caliper is most should important 350F (177C) at temperature this point. it indicates fluid where cooling

air is minimal. Caliper should not exceed 350F (1 7 7 C ) at this point.

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+ L27 L FL1 Wear = = La - LF Wear

Wear =top Lo -= LFNo. of Stops Wear/S Wear 1000 x Wear Stops of Stops Wear /1000 = No. =of No. Stops Wear/Stop 1000 x Wear Wear/1000 Stops = No, of Stops

LO

Wear per stop can be calculated using simple formulas shown. If pads weQr in a taper, use I average final thickness T f to compute wear. Usually, wear per 1000 stops is more usefulI than per can stop.beLining-wear calculations very important for long-distance racing. Wear wear per stop calculated using simple are formulas shown. If pads wear in a taper, use Wear perfinal lap or wear per T, hour be most important pad per changes be planned fuel average thickness to may compute wear. Usually,so wear 1 0 0 0can stops is more at useful stops.wear Have make quick calculations lining checks during tire changes to double-check than per crew stop. Lining-wear are very important for long-distance racing. calculations. Wear per lap or wear per hour may be most important so pad changes can be planned at fuel

stops. Have crew make quick lining checks during tire changes to double-check calculations.

car, watch out for uneven braking. The driver can lose control! car, for careful uneven you braking. Nowatch matterouthow are, T h e driver lose control! there are can always test-to-test difNo matter howeliminated careful you are, ferences that are by runthere are always test-to-test difning both configurations at once. ferences that are eliminated by runRerunning a test with the configuraning both configurations once. tions switched and averagingat results Rerunning side-to-side a test with differences the configuraeliminates . tions switched and parts averaging results When evaluating designed to eliminates run in oneside-to-side direction differences. only, such as When evaluating to curved-fin rotors, beparts suredesigned to switch run in oneyou direction only, such as parts when switch sides. curved-fin rotors, be sure to can switch Brake-Wear Test-Brake wear be parts when you switch sides. tested only after many stops. Earlier

Brake-Wear Test-Brake wear can be tested only after many stops. Earlier

in this chapter 1 suggested measuring lining thickness befo re testing. If you in this suggestedlining measuring do this,chapter you canI measure thicklining afterward thickness before testing. you ness to judge wear.If The do this, you can measure lining But thickamount of wear is interesting. to ness afterward judgeto wear. The be useful, you toneed determine amount wear is interesting. But to wear per of SlOp. beTouseful, you wear need per to determine calculate stop, you wear stop. the number of stops or must per know Tooncalculate stop, you laps the pads.wear You per should be able must know the number of stops or to find this in your records if you laps on the pads. Youin should be able recorded everything your notebook to suggested. find this in your records if you as recorded everything your notebook After you finish in testing, measure as suggested. brake-lin ing thickness. Measure the

After you finish testing, measure brake-lining thickness. Measure the

119

,r /

pad Backing Plate

/

Plate

Riveted Lining

Bonded Lining

Lining

When measuring lining thickness to compute wear rate, take several measurements and them. Because brake Whenaverage measuring lining thickness to shoes comand weartake unevenly, rates are pute pads wear rate, severalwear measurements based on average over the lining. To and average them.wear Because brake shoes compute lining thickness, look are for and padsminimum wear unevenly, wear rates thinnest based onspot. average wear over the lining. To

compute minimum lining thickness, look for thinnest spot.

linings in the same places as before and compare thicknesses to the origilinings in the sameWear places is as the before original measurements. and compare thicknesses to the original thickness minus the thickness nal measurements. is theatorigiafter testing. Look Wear carefully the nal the onthickness liningthickness to see if minus it is worn a taper. after testing. Look carefully Make a diagram to recordat the the lining to see if it is worn a taper.. information, as shown in theondrawing

Make a diagram to record the ｾ＠ the drawing. Lining-wear per stop = in information, as shown Lining-wear stop in inches perper stop

=r W

W = Total amount of lining wear in in inches per stop inches W Total amount of lining wear in N = =Total number of stops inches The answer from this formula will Total number of stops N=

be very small. So, multiply it by 1000 answer this formula will This figure to The get wear per from 1000 stops. it by 1000 be very small.toSo, will be easier use multiply . to Once get wear 1000 stops. This figure you per have wear per stop, calcuwill be easier to use. late the number of stops it takes to Once have wear completely. per stop, calcuoutyouthe linings To wear late this, the number stops it takes to lining do find theof minimum wear out the linings completely. To thickness allowed. Your car manudo this, find lining facturer or the brakeminimum manufacturer thickness allowed. Your car manushould be able to supply this facturer or Obviously, brake manufacturer information. you shouldshould able to to wear supply this n't allow be the lining so much information. Obviously, you shouldthat the metal backing plate contacts n't to wear much the allow rotor.the Or,lining if you havesoriveted that the it's metal contacts the backing distance plate the rivets are linings, the rotor. into Or, the if you havethat riveted recessed lining you linings,be it'sconcerned the distance should with.the rivets are recessed the lining give that miniyou Most carinto manufacturers

should be concerned with. Most car manufacturers give mini-

120

--1 __

pad Backing Plate k:king Plate

Rivet Head

Minimum Lining Thickness

+Minimum Lining

--11---c

1I

-t

Minimum Lining Thickness

Minimum Lining Thickness

To compute number of stops available from a new lining, you must know its minimumThickness I allowable lining thickness. This is different for riveted and bonded linings. Use depth-gageI

endcompute of dial caliper to measure lining.you More wear will result in rotor To number of stops available availablewear fromofa riveted new lining, must know its minimumor drum scoring. allowable lining thickness. This is different for riveted and bonded linings. Use depth-gage end of dial caliper to measure available wear of riveted lining. More wear will result in rotor or drum scoring.

mum lining thickness in their shop manual. If you can't find this figure, mum thickness in their shop assumelining you can wear the linings to manual. If you can't find this figure, within 1/16 in. of the plate or rivets. assume youminimum can wearlining the linings to Subtract thickness withinthe 1/16 in, of theofplate or rivets. from thickness a new lining to minimum liningwear. thickness getSubtract maximum allowable You from the thickness of a new lining to can then calculate the maximum get maximum number of stops: allowable wear. You

can then calculate the maximum W number of stops: Number of stops allowed

=_M_

Ws

WM Number of stops allowed = W M = Maximum lining wear w allowed in s inches W, Maximum wearinallowed Ws == Lining wearlining per stop inches in inches per stop W, = Lining wear per stop in inches perRemember stop that brake wear in-

creases with temperature. And, if you Remember that horsepower, brake wear the inincrease engine creases with temperature. And, if you brakes will get hotter because you'll increase horsepower, the be stoppingengine from higher speeds. Wear brakes willwill get also hotterincrease. because Aeroyou'll per stop be stopping from higher Wear dynamic changes also speeds. affect lining per stop will also increase. Aerotemperature and wear. Therefore, dynamic changes alsothickness affect lining keep records of lining each temperature and the wear.brakes. Therefore, time you inspect Also keep records of lining each record the number of thickness stops between time you inspect the brakes. Also inspections so you can keep track of record thewear number stops track between changing ratesof from to inspections so you can keep track of to setup. track and setup changing wear from track to Wear rates willrates change dramatically track and setup to setup. from track to track. One with long Wear rates dramatically straights and will tightchange flat turns is much

from track to track. One with long straights and tight flat turns is much

harder on brakes than one with short straights and high-banked turns. harder on brakes than one are withimporshort Lining-wear calculations straights and high-banked turns. tant in long-distance road racing. If Lining-wear calculations are aimporyou wear out linings and ruin rotor, road inracing. If of long-distance time will be lost the pits atant lot in you wear out linings and ruin a rotor, changing it. By determining lining awear lot during of timepractice will besessions lost in and the calpits changing it. number By determining of stops orlining laps culating the wear during sessions calallowed, youpractice can predict howandmany culating the number of stops or laps laps you can run before changing allowed, you can predict how sets many to have enough of pads. Be sure laps can run pads you bedded-in to before go the changing distance pads. have enough sets of thesure race to starts. beforeBe pads bedded-in to go the isdistance This sort of calculation useful before the race starts. only for race cars. Usually, you can This sort both of calculation useful determine wear rate isand the only for race of cars. Usually, can exact number possible stopsyou before determine wear rateTheand the is necessary. brakes a pad changeboth exact number of possible stops before are always used as hard as possible, so athepadwear change TheOn brakes rateisisnecessary. predictable. the are always as hard as possible, so street, the used number of stops depends the wear rate is predictable. On the on the type of driving . City driving street, stops depends takes the morenumber stops of than freeway on the type of driving. driving driving. Fast driving in theCity mountains takes more stops than freeway is a lot different than taking the family driving. Fast driving in the calculating mountains Therefore, to the drive-in. is a lot different than taking family wear per stop is impossiblethe . So, for to the drive-in. street use, keepTherefore, a record calculating of the car wear per each stop is impossible. So, are for mileage time the brakes street use, keep a record of the car inspected. This, along with a record of mileage each time the you brakes are lining thickness, will give an idea inspected. This,miles alongyour with brakes a recordwill of of how many lining thickness, will give you an idea last.

of how many miles your brakes will last.

Maintenance Proper maintenance is essential for brake-system safety and performance. maintenance essential for If Proper you have a good is maintenance brake-system safety and performance. program, you can usually find a probIf have a good serious. maintenance it becomes Don't lemyou before program, can usually find a occur probwait untilyoubrake problems lem before becomes serious.may Don't enbefore doingitsomething-you wait until brake problems occur counter a life-threatening situation. before doing system something-you maymost enThe brake is one of the counter a life-threatening situation. critical parts of a car. Luckily, brakes brakereliable, system iseven one of the most areThe very with poor critical parts of a car. Luckily, maintenance . Brake trouble can brakes usualarebe very even poor ly sensedreliable, at the pedal , sowith the driver maintenance. Brake trouble usual-, knows it immediately. For can example ly sensed at the pedal, the driver and so lower if the thebepedal gets lower knows it immediately. For brakes need adjusting. Andexample, it goes the pedal getsinto lower lower if the theand system through soft if air gets brakesseals. need Worn-out adjusting. linings And it make goes bad soft if air gets into the system through horrible noises as metal contacts bad seals. liningsevident make Most Worn-out problems become metal. horrible noises as metal contacts before a total brake failure occurs. metal. problems become evident One Most of the most dangerous probbeforeisa total brake occurs. This a line or failure hose failure. lems One of problem the mostcan dangerous probpotential go unnoticed lems is a line or hose failure. This, until the brakes are used hard . Then problem can can go occur unnoticed rupture with apotential line or hose until the brakes are used hard. to Then, the pedal suddenly dropping the afloor. line If or the hosecar rupture occur dualwith has a can modern the pedal suddenly dropping to the braking system , the driver can usually floor. If the modern car. car But,hasif athe systemdualhas stop the braking driver can andusually is in only twosystem, wheelsthebraking stop car. But, if the system has of maintenance, it may be imneed the only twoto wheels brakingOnly anda is in possible stop quickly. good need of maintenance, it may impreventive-maintenance effortbe will possible to stop quickly. Only a good prevent such problems. preventive-maintenance effort plan will Schedule-A good maintenance prevent problems. If the car is raced, requires such a schedule. Schedule-A goodbrake maintenance plan maintenance always do some requires a schedule. If the car is raced, before each race. Inspect the system always some brakeAlso maintenance for weardoand damage. bleed the beforebefore each each race. event. InspectIf the fluid yousystem fail to for this, wearbrake and performance damage. Alsowill bleed the suffer. do fluid before each event. If you fail to On a race car, major brake-system do this, brake performance will suffer. maintenance is done each season - or On often a race ifcar, major brake-system more problems occur. Major maintenance doneinclude each season-or maintenance ismay replacing more oftenand if problems Major the seals surfacing occur. or replacing maintenance may include replacing the rotors. Wheel-bearing lubrication theusually seals done and at surfacing is this time.or replacing theOnrotors. Wheel-bearing lubrication a road car, your shop manual is usually done at this time. will give a recommended brakeOn a road schedule. car, yourUsually, shop manual maintenance it sugwill give a recommended brakethe fluid level and gests inspecting maintenance schedule. it sugchecking the linings for Usually, wear after cergests inspecting fluid level You and tain mileage has the accumulated. checking the linings for wear after cercan modify this schedule if you find tain mileagebuthasthe accumulated. You manufacturer's problems,

can modify this schedule if you find problems, but the manufacturer's

II

Brake maintenance on race car should be done after each time car is raced. Mechanic prepares to disassemble and inspect brakes on this Indy Car after a practice session. He is using cleaningonfluid remove Cleanliness when workingpreon Brakebrake maintenance racetocar shouldcontamination. be done after each time carisisvital raced. Mechanic brakes.to disassemble and inspect brakes on this lndy Car after a practice session. He is pares

using brake cleaning fluid to remove contamination. Cleanliness is vital when working on recommendation is a good place to BRAKE ADJUSTMENT brakes.

start. Here is my brake-maintenance

recommendation a good place to schedule for a roadiscar: start. Here is my brake-maintenance Every 5000 miles: Inspect hoses schedule a road car:level. and lines;for check fluid Every 10,000 5000 miles: Inspect linings hoses Every miles: Inspect andwear. lines; check fluid level. for Every year: Every 10,000 25,000 miles: miles Inspect or everylinings for wear. Replace brake fluid . Every 25,000 or every year: Every 50 ,000miles miles: Overhaul Replace brake fluid. calipers; wheel cylinders, master Every 50,000 miles: Overhaul cylinder. calipers; wheel cylinders, This maintenance schedulemaster does cylinder. not cover everything. It just outlines schedule does theThis mostmaintenance common items and approxinot cover everything. It just outlines mates brake-maintenance needs. the most items and approxiYour car'scommon needs depend on its design mates and how brake-maintenance it's used . If the car needs. is not Your needs its design drivencar's often, youdepend shouldoninspect the and how used. If the the car is not fluid andit'soverhaul hydraulic driven often, inspectthan the system at you lowershould mileage fluid and overhaul thelining hydraulic recommended . Although wear system not at belower mileage than should a problem, corrosion recommended. Although lining wear and seal leakage may be, because time should be ofa aproblem, corrosion becomesnot more factor. and seal leakage may be, because time becomes more of a factor.

Brake adjusting is not needed with BRAKE ADJUSTMENT many cars. Disc .brakes are self adjustBrake adjusting is notbrakes needed with usually ing and modern drum many cars. Disc,brakes are self adjusthave automatic adjusters. If your car ing such and modern has features,drum forgetbrakes brake usually adjusthave automatic adjusters. If yournew car ment except when installing has such features, forget brake adjustdrum-brake linings. Often, a drum ment exceptbe when installing brake must adjusted manuallynew to drum-brake linings. adjuster Often, ato drum the automatic work allow brakefirst musttime. be adjusted manually to the Automatic adjusters allow the automatic adjuster to work only maintain clearance-they don't the first Automatic adjusters make largetime. adjustment changes. only clearance-they don't On maintain drum brakes without automatic make large adjustment changes. adjusters, periodic adjustment is On drum brakes wear, without automatic needed. As linings clearance beadjusters, periodic adjustment is and drum increases. tween the shoes needed. As linings wear, pedal clearance beThis results in more travel. tween theparking shoes and drum increases. brake requires more Also, the This results in more pedal travel. travel. You can usually tell when the Also, parking brakebyrequires more brakesthe need adjusting the increase travel. can However, usually tellifwhen the in pedalYou travel. you wait brakes need adjusting by the increase too long, the pedal may go to the floor in pedal fade travel. However, if youadjust wait if brake occurs. Therefore, too long, the pedal may go to the floor the brakes often; don't take risks.

if brake fade occurs. Therefore, adjust the brakes often; don't take risks. 121

＾ｩｾ＠ Torn I nner Lining Restricts Flow, Acts as Valve.

Torn Inner Lining Restricts Flow,

Fitting Leakage Seeps Out or Forms Bubble.

Fitting Leakage Seeps Out or Forms Bubble.

Although duo-servo brake uses automatic adjuster, brakes must be manually adjusted after brake-lining replacement. Although duo-servo brake usesBlade-type automatic tool is used to turn adjuster through slot in adjuster, brakes must be manually adjusted backing plate (arrow). after brake-lining replacement. Blade-type

tool is used to turn adjuster through slot in backing plate (arrow).

Inspecting and changing brake fluid is an important part of brake maintenance. Race car is getting filling of brake AP Racing fluid. Inspecting andachanging fluid is an Note reservoir cap withmaintenance. rubber bellows. It important part of brake Race isolates fluid from the of airAP when cap fluid. is in car is getting a filling Racing but allowscap fluid to rise and bellows. fall. place, Note reservoir with rubber It

isolates fluid from the air when cap is in place, but allows fluid to rise and fall.

Most modern road-car brakes are discs on the front and drums in the Most modern road-car brakes are rear. With this dual-braking system, discs on the front and drums in the only the drum-brake system can go rear. this dual-braking system, out ofWith adjustment. Typically there is a only the drum-brake switch system in can the go brake-warning-light out of adjustment. Typically there is system that senses excess movementa brake-warning-light switchWhen in the of the rear-brake fluid. the system that senses excess movement brakes need adjusting , more displaceof the is rear-brake fluid. the When the ment required than master brakes need adjusting, more displacecylinder can supply; the brake ment is required the on master turns the warning-light switchthan cylinder can This supply; thewillbrake warning light. switch also warning-light switch detect fluid loss causedturns by a on leakthe in warning light. This switch will also either system. detect fluid loss caused by agenerally leak in the rear brakes Adjusting either system. requires jacking up the car, supporting theunderneath rear brakes generally it, Adjusting and getting . There are

requires jacking up the car, supporting it, and getting underneath. There are

122

Bottom : Blistered brake hose is ready to fail. Replace such a hose immediately! Top: Hidden brake-hose failure restricts Bottom: Blistered brake hose is ready to flow to or fromsuch brake. Thin layer of inner fail. Replace a hose immediately! lining Hidden can lift off surface and restrict flow Top: brake-hose failure restricts of fluid This may to flow to to or brake. from brake. Thincause layer brake of inner apply laterliftonoffone side, and causing carflow to lining can surface restrict swerve. brake hoses shouldbrake be reof fluid toOld brake. This may cause to placed later as aonsafety precaution. apply one side, causingDrawing car to courtesy Bendix Corporation. swerve. Old brake hoses should be re-

placed as a safety precaution. Drawing courtesy Bendix Corporation.

many types of brake adjusters. One is a square bolt head projecting from the many types of brake adjusters. Onead-is backing plate. Most domestic-car a squarerequire bolt head projecting from justers inserting a tool intothea backing plate. Most domestic-car adslot in the backing plate and turning justers require inserting a tool into the star wheel. There may be one ora slot the backing plate and dependturning moreinadjusters on each brake, the on starthewheel. ing design.There may be one or more adjusters each brake, dependthe on shop-manual instrucFollow ing on the design. tions for brake adjustment. Be sure the shop-manual notFollow to overtighten the brakes. instrucA dragtions brake for brake adjustment. Because sure will overheat and can ging not to overtighten the brakes. A dragdamage, excess wear, lower mileage ging brake will overheat and can cause. or fade . damage, excess lower mileage Make sure the wear, parking brake is not or on fade. when adjusting rear brakes. Make sureyou thewon parking braketo.isThe not Otherwise, ' t be able on when adjusting rear brakes. parking brake is applied to the rear Otherwise, youare won't be able to. The brakes, which usually drums. You parking brake is applied to the rearif will think the brake is fully adjusted brakes, which are usually drums. You you try it with the parking brake on. will think the fool brake is fully adjusted if Don't let this you. you try it with thedrum-brake parking brake on. Normally, rear adjustDon't let this fool you.of parking-brake ment will take care Normally, rear drum-brake adjustment. Except on some adjustfourment will take care of wheel, disc-brake cars,parking-brake you should adjustment. on the someparking fournever need Except to adjust wheel, disc-brake cars, you should brake unless it won't work ajteradjustnever to adjust the parking ing the need rear brakes. Parking-brake adbrake unless it won't work afteradjustjustment is discussed on page 135.

ing the rear brakes. Parking-brake adjustment is discussed on page 135. HYDRAULIC-SYSTEM INSPECTION HY DRAULIC-SYSTEM Besides brake adjustment, the most INSPECTION common maintenance item is checkbrake adjustment, ingBesides the hydraulic system . To the be most safe, common maintenance item is check the fluid level about everycheck5000 ing the Fluid hydraulic system. be safe, miles. leakage can To cause total check the fluid about every 5000 brake failure onlevel a single brake system. miles. Fluidcause leakage can cause It can also problems on a total dual brake failure on a single brake system. It can also cause problems on a dual

system . If you discover that fluid level has dropped each time you look at it, system. If you discover level problem andthat fixfluid it. Fluid locate the has dropped each time you look at it, shouldn't leak from a brake system. locate the aproblem it. Fluid Typically, leak canand be fix traced to a shouldn't leak from a brake defective wheel-cylinder seal, system. caliper Typically, a leak canOr,be atraced or master-cylinder. leak to maya defective wheel-cylinder seal, caliper occur at a fitting or hole in a line or or master-cylinder. a leak brake hose. Look forOr,drips and may wet occur near at a the fitting or holesystem. in a line or areas hydraulic Fluid brake hose. Look for drips and wet be fixed immeleaks should areas near the hydraulic system. diately-procrastination can Fluid be leaks should be fixed immedangerous! diately-procrastination can , you be In addition to fluid level dangerous! should check all brake hoses and In This addition to done fluid while level,youyou lines. can be ' re should check all brake hosesunder and performing other maintenance lines.car, This canasbeadjusting done while the such the you're brakes performing other maintenance or doing a lube job. Inspect the under brake the car, as adjusting theLook brakes both ends of the car. for hoses at such or doingchafe a lube job. Inspect brake. cracks, marks, or otherthe damage hoses at both the car. Look for on aends hoseofindicates failure. A lump cracks, chafe marks, or other damage. Fluid can seep through the first few A lump a hose indicates layers of on reinforcing cord and failure. form a Fluid can seep through the If first few lump or blister on the hose. a hose layers reinforcing cord and form Don'ta blisters,ofreplace it immediately. lump orsudden blister brake on the hose. If a hose chance failure. blisters, replace it immediately. Occasionally, a pinhole in a Don't brake chance sudden brake failure. hose can allow air to get into the brake Occasionally, pinhole a brake fluid . The hole acan be theintype that hose can allowwhen air to get the brake leaks only the into brakes are fluid. The drawing hole can in be the that released, air, type creating leaks when the brakes are bubblesonly . When pressurized , this leak released, drawing not let in fluidair, out. creating If your can seal and bubbles. When this leak brake hoses arepressurized, old and weathered, can seal and not let fluid out. If your replacing them may cure a recurring brake hoses are old and weathered, spongy pedal. replacing them may a recurring can cure fail because of Brake hoses spongy pedal. improper installation. If a hose is Brake or hoses can fail of twisted installed in because the wrong improper installation. If a hose is position, it can break. Or, if a car is twisted onor rough installed in large the wrong driven terrain, wheel position, it can if a car is movements can .break. strain Or, a brake hose. driven on rough terrain, large wheel Also , hoses can be damaged by rocks movements can strain or road debris throwna brake up byhose. the Also, damaged by rocks I've can seenbebrake-hose damage wheels.hoses or roadbydebris thrown over up bydebris the caused a car running wheels. I've seen brake-hose damage that gets tangled in a wheel and caused a car running over debris wrappedby around the brake hose. that getscause tangled in damage a wheelis and Another of hose letwrapped aroundcaliper the hang brakefrom hose. ting a disc-brake its Another cause of hose damage lethose during maintenance: Use ofis corting disc-brake caliper hang fromwill its procedures rect a maintenance hose during of coravoid such maintenance: potentially Use dangerous rect maintenance procedures will situations. avoid potentially Check such Clearances - If yourdangerous car has situations. wide wheels, fat tires , or other suspenCheckmodifications, Clearances-If look yourforcarchafe has sion wide fat tires, other. suspenmarkswheels, on the brakeorhoses A tire sion modifications, look for touching a hose eventually can chafe wear marks on the brake hoses. tire through it. Even something Aminor touching a large-diameter hose eventuallyheavy-duty can wear like a set of throughcanit.cause Evensimilar something minor shocks problems.

like a set of large-diameter heavy-duty shocks can cause similar problems.

To check clearances, turn the front wheels to full right and left lock and To check the sides. front check them.clearances, Check atturn both wheels to full right and left lock the Clearances may not be exactly and check Jack them.upCheck at and bothlook sides. same. the car at Clearances with may the not wheels be exactly the clearance at full same. at Next, up jacktheup car oneand rearlook wheel. droop. Jack clearance with the wheels at full This will compress the diagonally droop. jack suspension. up one rear wheel. Check oppositeNext, front This will compress thethediagonally clearances, then jack up opposite oppositeandfront suspension. Check corner recheck. Conditions and clearances, then jack up the opposite clearances change a great deal as the corner and recheck. Conditions wheels travel up and down as they and are clearances great deal as the steered. Trychange every apossible combinawheels up Although and down front as they are tion to travel be sure. hoses steered. Try every possible combinahave the most clearance problems, tion to be sure. hoses particularly whenAlthough turning, front check the havehoses the as most rear well.clearance problems, particularly turning, the If your carwhen has been usedcheck off road, rear hoses as well. check the condition of the steel brake If your car the has car. beenIt's used off road, lines under possible to check the condition of the steel brake pinch a line when going over a rough lines under It's possible to If youthe findcar. a damaged line, resurface. pinch a line when going over a rough place it. Look closely. A crack or a surface. a damaged thin spotIfisyou veryfind hard to see. line, replace it. Look closely. A crack or a If your car is older, check the steel thin hard to Rust see. can eat linesspot foris very corrosion. If yoursteel car is older, check the steel even though they through lines, lines for corrosion. Rust eat are about as corrosion-proof ascan science through steel lines, even though they can make them. The likelihood of are about as corrosion-proof science having rusty brake lines is as greater if can make them. T h e likelihood of you drive where salt is used on the havinginrusty greater if roads the brake winter.lines You iscan expect you drive where salt is used on the trouble from salt-water spray. Older roadsfrom in the Youand canMidwest expect cars the winter. Northeast trouble from salt-water spray. Older are likely to require brake-line cars from the Northeast and Midwest replacement. Rusty brake lines is a are to require brake-line usual likely problem on vintage cars. replacement. Rusty brake lines is a most restorers replace Consequently, usual problem on vintage cars. them without bothering to check . Consequently,the most restorers Remember, inside rustsreplace from them without bothering water in the brake to fluidcheck. as Remember, the inside rusts check from well-something you can't water visually. in the brake fluid as

well-something you visually. BRAKE BLEEDING

can't

check

Bleeding is important to proper

BRAKE BLEEDING brake-system maintenance. It is usualBleeding is important to trapped proper ly done to remove air bubbles brake-system maintenance. in the system. Bleeding isIt isa usualmust ly donetime to remove air bubbles trapped every the hydraulic system is in the system. Bleeding opened up for any reason is . Ita ismust imevery hydraulic is possibletime to the prevent some system air from opened uptheforsystem any reason. It is imentering if a fitting is possible prevent some from loosened. toMost systems haveairnumerentering system a fitting is ous high the spots whereif air will be loosened. Most systems have numertrapped . ous highbleeding spots can where air will be Brake be frustrating or trapped.depending on the system easy, Brake Some bleedingbleeders can be frustrating or are reached design. easy, depending on the system easily on the inboard side of the design. Someunderneath. bleeders are brakes, from On reached others, easily on bethe inboard of the they may tucked insideside the suspenbrakes, from underneath. On others, they may be tucked inside the suspen-

Someone previously installed wide wheels on myoid Ford truck, but didn't check brake-hose clearanceinstalled with front wheels at Someone previously wide wheels full my lock.old After some use,but wheel-rim edge on Ford truck, didn't check rubbed through line,with causing a leak. brake-hose clearance front wheels at Fortunately, was discovered full lock. Afterdamage some use, wheel-rim edge during maintenance, rather athan by rubbed brake through line, causing leak. "accident." Fortunately, damage was discovered during brake maintenance, rather than by "accident!'

sion where they are real "knuckle busters" to get at. Some systems also sion theyother are real have where bleeders than"knuckle at the busters" to get at. Some also the master wheels, such as on systems have bleeders at the cylinder. Consultother your than shop manual wheels, such bleeders. as on the for any hidden If youmaster miss cylinder. Consult your shop manual one, you will wonder why your pedal for any hidden bleeders. If you miss is spongy even after bleeding. one, you will wondercan whyusually your pedal Bleeder screws be is spongy even after bleeding. turned with a small Six-pOint box-end BleederA void screwsusing can anusually be wrench. open-end sk-point box-end turned with a small wrench to prevent rounded-off bleedwrench. using knuckles. an open-end er screwsAvoid and bloody For wrench to prevent rounded-off bleeddifficult-to-get-to bleeders, special er screws and bloody knuckles. For bleeder wrenches are available at autodifficult-to-get-to bleeders, special parts stores. These look like a box-end bleeder wrenches available at autowrench with a hugeare offset. parts look like box-enda that there is ausually Be stores. aware These wrench with a huge offset. bleeder at each brake, but some sysBe use aware that there usually tems a single bleederis to servicea bleeder each brake, but some sysboth rearatbrakes. tems use anormally single bleeder to at: service Bleeders are found both rear brakes. • Each drum-brake wheel cylinder. normally are found two at: or caliper• Bleeders Each disc-brake Each drum-brake wheel more bleeders may be used.cylinder. or Outlet disc-brake port at caliper-two some master • Each more bleeders may be used. cylinders, particularly those mounted O an u t angle. l e t port at some master at cylinders, those mounted combination valves used • On someparticularly at an angle. with disc brakes. On some combination used • On accessories, such valves as trailer with disc brakes. brakes. On accessories, as trailer Don't forget to looksuch for bleeders on brakes.sides of a disc-brake caliper. both Don't forget to look for bleeders bleeders on Some fixed calipers have on both sides where of a you disc-brake caliper. the inside would expect, Some fixed calipers have bleeders plus another on the outside hidden on by the inside where you would expect, the wheel. If you don't remove the plus another on the by wheel, you'll missoutside the hidden outboard the wheel. If you don't remove the bleeder. wheel, you'llto miss replacethetheoutboard rubber Be sure

bleeder. Be sure to replace the rubber

When brake line rusts, fittings can seize on steel tube. This can happen when seized fitting brake is turned with a wrench. When line rusts, fittings canAlthough seize on such tube. a lineThis maycan nothappen leak, it should be steel when seized replaced. fitting is turned with a wrench. Although such a line may not leak, it should be replaced.

Brake bleeding can be awkward and messy. Consequently, it's easy to do the job wrong or miss a bleeder. Take your Brake bleeding can be awkward and time, the job right, messy.plan Consequently, it'sand easyuse to correct do the tools. Startorbymiss jacking up theTake car your and job wrong a bleeder. removing wheels to improve access. time, planthe the job right, and use correct tools. Start by jacking up the car and removing the wheels to improve access.

bleeder-screw caps if your brakes have them . They protect the bleederbleeder-screw caps if from yourmoisture brakes screw seat and threads have them. They protect the bleederand prevent corrosion seizure. These screw seat andcan threads from moisture caps, which be purchased from and prevent dealers, corrosionareseizure. Volkswagen a goodThese addicaps, cancar.be purchased from tion towhich any road Volkswagen dealers, are involves a good addiAnother frustration the tion to any road car. metering valve used on some road Another frustration involves the cars. A special clip is used to hold this metering on can some road valve openvalve so theused brakes be bled.

cars. A special clip is used to hold this valve open so the brakes can be bled. 123

Note that caliper has a bleeder on each side. Forget to remove the wheel and you'll miss bleeding outboard side. This can result in a spongy pedal. Photo Note that caliper hascourtesy a bleederAP onRacing. each side. Forget to remove the

wheel and you'll miss bleeding outboard side. This can result in a spongy pedal. Photo courtesy AP Racing.

Pressure bleeder is used in most repair shops because of its speed. Huge can of fluid is used to fill pressure bleeder. Because most racers fear possible of oldrepair or contaminated fluid, of presPressure bleeder is used use in most shops because its sure bleeders areofnot popular. road cars, they offerBecause speedy speed. Huge can fluid is usedFor to fill pressure bleeder. low-cost brake bleeding in ause shop. most racers fear possible of old or contaminated fluid, pres-

sure bleeders are not popular. For road cars, they offer speedy low-cost brake bleeding in a shop.

If it's not held open , the brakes can't be fully bled. If Consult it's not held brakes the open, shop the manual forcan't the be fully bled. correct information on your car. If Consult the shop thea you don ' t have a shopmanual manual,for visit correct information on your It's car.too If car dealer and ask a mechanic. you don't have a shop manual, dangerous for guesswork in thisvisit area.a car a mechanic. too Youdealer may and also ask have to buy a It's special dangerous for guesswork in this area. tool from the dealer. This tool is often may also have to to buy special aYouspring designed flex awithout tool from the often damaging thedealer. valveThis as tool fluidis flows athrough springit. designed to flex without damaging the as fluid flows Sequence of valve Bleeding - Bleeding throughbe it. done in a specific sequence should Sequence to avoid the of need Bleeding to double-Bleeding back and should be done in specific sequence sequence if rebleed . Follow athis to avoidbleeding the need double you're onetowheel at aback time:and rebleed. this itsequence if cylinder-if is bleeder • Master Follow you're bleeding one wheel at a time: equipped. l Master cylinder-if • Combination valve. it is bleeder equipped. • Bleeders on intermediate hardware l Combination valve. in system. l Bleeders on intermediate hardware from master • Wheel farthest in system.usually the right rear wheel. cylinder, W h e eIfl wheel farthest from have master Note: cylinders two cylinder, the one rightfirst; rear if wheel. bleeders, usually do upper a caliNote: wheel cylinders have one two per hasIftwo bleeders, do inboard bleeders, do upper one first; if a califirst. If it has more, follow the manuper has two recommended bleeders, do inboard one facturer's bleeding first. If it has more, follow the manusequence. facturer's recommended bleeding other brake at that • Bleed sequence. end - usually left rear. e e d next otherwheel brake at from that farthest •B lBleed end-usually left rear. right front. master cylinder-usually Bleed next farthest from •l Bleed wheel wheel remaining-usually master cylinder-usually right front, left front. l Bleed wheelbleeding remaining-usually After the process is left front. check the system by presscomplete,

After the bleeding process is complete, check the system by press-

124

ing hard on the pedal to be sure it stays firm. If the pedal is spongy, reing on or thecheck pedalfortoa leak. be sure it bleedhard system stays firm. If the pedal is spongy, reTo check for air in the brake bleed system or check for a leak. system, have someone pump the To several check times, for airthenin hold the it brake pedal down system, have the remove thepump reservoir firmly while yousomeone pedal several times, then hold it down cap. Watch the fluid surface while firmly helper while you remove the reservoir your slides his foot off the cap. the pedal fluid snaps surface pedal Watch pad so the backwhile and your slidesdrops his immediately. foot off the systemhelper pressure pedal apad so the pedal snaps back With well-bled system, there willand be' system pressure drops immediately. a little turbulence at the surface of the With system, there will1/4 be' fluid. aIfwell-bled fluid boils up more than ain.little turbulence at the surface of the above the surface, there's probably fluid. If fluid boils up more than 1/4 system. air in the in. above the surface, there'scommonly probably Bleeding Methods - Three air in the system. for brake bleeding used techniques Bleeding Methods-Three commonly are: used techniques for brake bleeding bleeding. • Pressure are: • Manual bleeding. l Pressuremethods, bleeding. such as gravity • Special l Manual bleeding. bleeding or vacuum bleeding. l Special suchargue as gravity These allmethods, work. People which bleeding or vacuum bleeding. method works better. All good arguTheseare all so work. People that arguenothing which ments complex method better. good argube settled . So,All I suggest that will everworks ments are so complex that method, nothing if you have trouble with one will ever beuntil settled. try another youSo, findI suggest the one that that if you best havefor trouble with one method, works your car. tryI'll another until you of findthe theproblems one that explain some works best for your car. with each method. Then I'll explain I'lleach explain job issome done. of the problems how with each method. Then requires I'll explaina Pressure bleeding how each job is done. pressure-bleeder tool. The pressure Pressure bleeding requires bleeder pressurizes the fluid in thea pressure-bleeder tool. The you pressure reservoir. Once pressurized, open bleeder pressurizes fluid innoted the sequence each bleeder in the the

reservoir. Once pressurized, you open each bleeder in the sequence noted

until no air is left in the system. The advantage of pressure bleeding until is leftand in the is thatnoit air is fast onesystem. person can do The advantage of pressure the job. But, there are bleeding several is that it is fast and one person can do disadvantages: The tool is expensive the ajob. But, are several fluidthere is wasted. If you and lot of disadvantages: The toolbleeder is expensive don't use the pressure often, and a lotin of fluidcontaminated, is wasted. If even you the fluid it gets don't use the pressure bleeder often, though it' s in a sealed container. theFluid fluid flow in it gets contaminated, if a in the lines is higheven though a sealed container. bleeder it'sis inopened too far during Fluid flow the cause lines isbubbles high if toa Thisin can bleeding. bleeder is opened too far form within the system from during turbubleeding. Thisas can causeflows bubbles to lence created the fluid around form within system fromtheturbudefeats pursharp corners.theThis lence created as the Conversely, fluid flows around pose of bleeding. rapid sharp corners. This defeats the purair trapped in fluid flow flushes out pose bleeding. rapid system . Bubbles high of spots in the Conversely, fluid flow trapped in clinging to flushes the wallsout of air rough compohigh spots in the system. Bubbles nents will be washed away by the flow. clinging to the the pros wallsand of rough is not With all cons, itcomponents if willpressure be washed away byis the flow. good or clear bleeding With all the pros and cons, it is it bad . Most auto-repai r garages usenot clear if pressure or fastbecause pressure bleeding bleedingis isgood bad. use it most Most racers,auto-repair don't duegarages to potential because pressure bleeding fluid-contamination problems.is fastmost racers,bleeding don't due to advantage potential Pressure has an fluid-contamination problems. on an older car which has had little Pressure bleeding The has an advantage brake maintenance. master cylinon older which hasstroked had little notcar have to be to der an does brake maintenance. Thesystem master cylinpush fluid through the . This is der does have to be stroked to unlike thenot manual-bleeding method push fluid through the system. is that requires full strokes of theThis brake unlike theanmanual-bleeding pedal. On older car, there method may be that requires themaster brake corrosion andfull dirtstrokes insideofthe pedal. On an older car, there may be cylinder. Stroking the pedal to the corrosion andthedirt inside theinto master moves piston deep the floor cylinder. Stroking the itpedal the master cylinder, where would to other-

floor moves the piston deep into the master cylinder, where it would other-

Most racers prefer manual-bleeding method : One person opens and closes bleeders while helper operates brake pedal. Although optional, it's helpful for third person to watch reservoir add fluid when needed. Method is reliable, but success on communication Mostand racers prefer manual-bleeding method: One person opensdepends and closes bleeders while between those doing job. helper operates brake pedal. Although optional, it's helpful for third person t o watch reser-

voir and add fluid when needed. Method is reliable, but success depends on communication between those doing job.

wise never travel. Corrosion and dirt would likely damage the seals, causing wise travel. Pressure Corrosion bleeding and dirt them never to leak. would likely damage the seals, causing avoids this. them to leak. Pressure bleeding Manual bleeding is cheaper, but reavoids this. quires at least two people; while one Manualthe bleeding cheaper, reoperates pedal, isthe other but opens quires at least two people; while one and closes the bleeders. The fluid operates the other opens reservoir the has pedal, to be topped up during and closes the bleeders. the bleeding process. FluidThe flowfluid can reservoir has todepending be toppedonuphow during be fast or slow, fast the process. and Fluidhow flow can the bleeding pedal is pushed much be fast or slow, depending on how fast each bleeder is opened. Manual bleedthe pedal is pushed better and how ing can be controlled thanmuch preseach bleeding bleeder is, so opened. Manual bleedsure most racers prefer it. ing be job controlled Andcan , the wastes better little than fluidpresand sure bleeding, most racers prefer it. doesn't requireso expensive tools. And, the job wastes little fluid and Gravity bleeding can be done only doesn't require expensive tools. with certain brake systems. As you Gravity beforms done bubonly know, air inbleeding the brakecan fluid with certain brake systems. As bles that float to high points in you the know, thehigh brake fluid bubsystem.airIfin the point is forms the master bles that float high points the cylinder, air to will come in out system. If the high point is the master automatically. cylinder, air will out Gravity bleeding is notcome used often automatically. because it takes too long. Also , in Gravity bleeding not used almost every brake is system, thereoften are because takesmake too itlong. Also, . in If high spotsit that impossible almostareevery brake system, are you designing a brakethere system high spots that you makemay it impossible. If from scratch, be able to you system make areit designing possible toa brake self-bleed by from scratch, yousystems may be to gravity, but most are able not demake it possible to self-bleed by signed that way. gravity, but most systems aredone not deby Vacuum-bleeding can be signed that way. one person. A small hand-operated

Vacuum-bleeding can be done by one person. A small hand-operated

eTA Manufacturing's bleeder hose, available at many auto-parts stores, makes it possible for one person to manually bleed CTA Manufacturing's bleeder hose, availabrakes. Hoseauto-parts is slipped over makes bleeder, ble at many stores, it bleeder is and free end is put in possible foropened one person to manually bleed catch canHose or bottle. Fluid orover air can only brakes. is slipped bleeder, flow out isofopened hose. When pedal bleeder and free endcomes is putup, in one-way closes. This air catch canvalve or bottle. Fluid or prevents air can only from out entering hose. Using hose requires flow of hose. When pedal comes up, getting in valve and out of carThis to check for air one-way closes. prevents bubbles in hose andUsing fluid hose in reservoir. from entering hose. requires Photo byinRon getting andSessions. out of car t o check for air

bubbles in hose and fluid in reservoir. Photo by Ron Sessions.

Master Cylinder

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1

t'.

To 0 Reservoir To o

Master Cylinder

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Reservoir

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Gravity Bleeding or Caliper

Master Cylinder

I

-

.

Trapped Bubbles

Master Cylinder

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No Gravity Bleeding Possible or Caliper

Gravity Bleeding Bleeding If brake system is free of high spots that trap No air,Gravity bleeding can be Possible done automatically by gravity. Air bubbles rise to reservoir. If system has high spots in lines, as shown at right, system not gravity If brakewill system is freebleed. of high spots that trap air, bleeding can be done automatically by gravity. Air bubbles rise t o reservoir. If system has high spots in lines, as shown at right, system will not gravity bleed.

vacuum pump is attached to a jar-or plastic bottle-with a closed top. The vacuum is attached to ableeder. jar-or jar has a pump hose that goes to the plastic bottle-withfrom a closed Air is evacuated the jartop. and The the jar has a ishose that goes the bleeder. bleeder opened. The to vacuum pulls Air evacuated from the the jar hydrauand the fluidisand air bubbles from bleeder is opened. The vacuum pulls lic system and into the jar. fluid and airbleeding bubbles sounds from theneat, hydrauVacuum but

lic system and into the jar. Vacuum bleeding sounds neat, but

it has a potential problem. Brakecylinder cup-type seals are meant to it haswith a potential problem. Brakework fluid pressure greater than cylinder cup-type seals are With meant the to the outside air pressure. work with fluid fluid pressure greater than vacuum pump, pressure is below the outside air. air This pressure. Within the the outside may draw air vacuum is below past the pump, seals, fluid unlesspressure your hydraulic the outside may drawI in system has air. cupThis expanders. donair 't

past the seals, unless your hydraulic system has cup expanders. I don't 125

Vacuum bleeder sucks fluid or air into container through tube connected to opened bleeder. Although tool is easy to use and requires only one person, I don't recommend it. Seals in brakes allowsucks air to be drawn if vacuum is applied totube brake fluid. Vacuumcan bleeder fluid or airininto container through connected to opened bleeder. Although tool is easy to use and requires only one person, I don't recommend it. Seals in

brakes can allow air to be drawn in if vacuum is applied to brake fluid.

Master Cylinder Bleeder Hose -Glassor Clear-Plastic Jar

Pressure Bleeder

Clear-Plastic Jar

Pressure bleeder setup: Pressure-bleeder tank is charged with compressed air, which pushes fluid into brake system. Adapter clamps to reservoir, sealing fluid entering system. Drawing courtesy Pressure bleeder Bendix setup: Corp. Pressure-bleeder tank is charged with compressed air, which

pushes fluid into brake system. Adapter clamps to reservoir, sealing fluid entering system. Drawing courtesy Bendix Corp.

Master Cylinder

1 3

Press slowly on brake ~ e d a l .

Bleeder Hose

,--1''-