Brake Technology

80

Brake System

Technology

Chapter

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© Goodheart-Willcox Co., Inc.

Objectives

After studying this chapter, you will be able to:
• Explain the hydraulic and mechanical principles of

a brake system.

• Identify the major parts of an automotive brake

system.

• Define the basic functions of the major parts of a

brake system.

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© Goodheart-Willcox Co., Inc.

Objectives

• Compare drum and disc brakes.
• Explain the operation of power brakes.
• Describe the operation of parking brakes.
• Correctly answer ASE certification test questions

requiring a knowledge of automotive brake
systems.

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© Goodheart-Willcox Co., Inc.

Brake System Technology
Introduction

• Automotive brakes

– Provide means of using friction to either slow, stop,

or hold wheels of vehicle

• Moving car has tremendous amount of stored

energy in form of inertia
– Tendency to keep moving

• To stop vehicle, brakes convert mechanical energy

into heat energy

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Brake System Technology
Introduction (Cont.)

• Hydraulic brakes

– Confined brake fluid used to transfer power and

motion from brake pedal to wheel cylinders and
brakes

• Hybrid brakes

– Conventional hydraulic brake system combined

with electric regenerative braking system provided
by hybrid’s driveline

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Basic Brake System

Basic parts include
• Brake pedal assembly

– Foot lever for operating master cylinder and power

booster

• Master cylinder

– Hydraulic-piston pump that develops pressure for

hydraulic brake system

• Brake booster

– Vacuum, electric, or power steering-operated

device that assists brake pedal application

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Basic Brake System (Cont.)

• Brake lines and hoses

– Metal tubing and rubber hose that transmit

pressure to wheel brake assemblies

• Wheel brake assemblies

– Hydraulic-mechanical mechanisms that use

hydraulic pressure to produce friction to slow or
stop each wheel

• Emergency or parking brakes

– Mechanical or electric systems for applying rear

brake assemblies

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Basic Brake System (Cont.)

(Honda)

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Drum and Disc Brakes

• Disc brakes are

frequently used on two
front wheels of vehicle

• Drum brakes are often

used on rear wheels

• Disc or drum brakes may

be used on all four
wheels

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© Goodheart-Willcox Co., Inc.

Drum and Disc Brakes (Cont.)

Components of disc brake assembly
• Caliper

– Assembly that holds hydraulic cylinder, piston,

seals, and brake pads

• Caliper cylinder

– Machined hole in caliper
– Piston fits into this cylinder

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Drum and Disc Brakes (Cont.)

• Brake pads

– Friction members that push against disc by action

of master cylinder, caliper cylinder, and piston

• Brake disc

– Large metal rotor that holds wheel and tire and

uses friction from brake pads to stop or slow wheel
rotation

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Drum and Disc Brakes (Cont.)

Components of drum brake assembly
• Wheel cylinder assembly

– Houses hydraulic piston that force outward by fluid

pressure

• Brake shoes

– Friction units that push against rotating brake drum

by action of hydraulic wheel cylinder

• Brake drum

– Rubs against brake shoes to stop or slow wheel

rotation

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Braking Ratio

• Comparison of front wheel braking effort to rear

wheel braking effort

• Typically, front wheel brakes handle 60%–70% of

the braking power

• Rear wheel brakes typically handle 30%–40% of

braking

• Front-wheel-drive cars can have even higher

braking ratio at front wheels

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Brake System Hydraulics

• Hydraulic system uses liquid to transmit motion or

pressure from one point to another

• Several principles apply to operation of hydraulic

system
– Liquids in confined area will not compress

• Air in confined area will compress

– When pressure is applied to closed system,

pressure exerts equally in all directions

– Hydraulic system can increase or decrease force or

motion

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Hydraulic System Action

(OTC)

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Brake System Components

• Know location and construction of major brake

system components

• This will better prepare you to troubleshoot and

repair these important parts

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Brake Pedal Assembly

• Lever arm increases

force applied to
master cylinder piston

• Manual master

cylinder bolts directly
to engine’s firewall

• Brake pedal assembly

bolts under dash

(Bendix)

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© Goodheart-Willcox Co., Inc.

Master Cylinder

Four basic functions
• Develops pressure, causing wheel cylinder pistons

to move toward discs or drums

• After all shoes or pads produce sufficient friction,

it helps equalize pressure required for braking

• Keeps system full of fluid as brake linings wear
• Maintains slight pressure to keep contaminants

from entering system
– Air and water

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Master Cylinder Construction

• Housing
• Reservoir
• Piston
• Rubber cup
• Return spring
• Rubber boot

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Master Cylinder Construction
(Cont.)

• Cup and piston

– Pressurize brake system
– When pushed forward, they trap fluid, building

pressure

• Intake port or vent

– Allows fluid to enter rear of cylinder as piston slides

forward

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Master Cylinder Construction
(Cont.)

• Compensating port

– Releases extra pressure when piston returns to

released position

– Fluid can flow back into reservoir through

compensating port

• Residual pressure valves

– Maintain residual fluid pressure of approximately

10 psi to help keep contaminants out of system

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Master Cylinder Construction
(Cont.)

• Rubber boot

– Prevents dust, dirt, and moisture from entering

back of master cylinder

• Master cylinder reservoir

– Stores an extra supply of brake fluid
– Reservoir may be cast as part of housing, or it may

be removable plastic part

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Dual Master Cylinder

• Older vehicles used single-piston, single-reservoir

master cylinders
– Dangerous

• If brake fluid leak developed, sudden loss of

braking ability could occur

• Modern vehicles use dual master cylinder for

added safety

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© Goodheart-Willcox Co., Inc.

Dual Master Cylinder
(Cont.)

(Bendix)

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Dual Master Cylinder
(Cont.)

• Dual or tandem master cylinder

– Has two separate hydraulic pistons and two fluid

reservoirs

– If there is system leak in one of hydraulic circuits,

other circuit can still provide braking action on two
wheels

• Rear piston assembly is called primary piston
• Front piston is secondary piston

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© Goodheart-Willcox Co., Inc.

Dual Master Cylinder Operation

(Delco)

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© Goodheart-Willcox Co., Inc.

Power Brakes

• Use booster and either engine vacuum, electric

pump, or hydraulic pressure to assist brake pedal
application

• Booster is located between brake pedal linkage

and master cylinder

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© Goodheart-Willcox Co., Inc.

Power Brake Vacuum Boosters

• Vacuum booster

– Uses engine vacuum to apply hydraulic brake

system

– Or vacuum created by separate pump on diesel

engines

• When vacuum is applied to one side of booster,

piston or diaphragm moves toward low-pressure
area
– This movement helps force piston into master

cylinder

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© Goodheart-Willcox Co., Inc.

Vacuum Booster Types

Two types of vacuum brake boosters
• Atmospheric suspended brake booster

– Has atmospheric pressure on both sides of

diaphragm or piston when brake pedal is released

• Vacuum suspended brake booster

– Has vacuum on both sides of piston or diaphragm

when brake pedal is released

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© Goodheart-Willcox Co., Inc.

Power Brake Hydraulic Boosters

• Hydraulic booster, hydro-boost or hydra-booster

– Uses power steering pump pressure to help driver

apply brake pedal

• Fluid pressure, instead of vacuum, helps force

piston forward

• Commonly used on vehicles equipped with diesel

engines

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© Goodheart-Willcox Co., Inc.

Brake Fluid

• Specially blended hydraulic fluid that transfers

pressure to wheel brake assemblies

• Automakers recommend brake fluid that meets or

exceeds SAE and DOT specifications
– Society of Automotive Engineers
– Department of Transportation

• Only use brake fluid that satisfies their

requirements

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© Goodheart-Willcox Co., Inc.

Brake Fluid (Cont.)

Brake fluid must have these characteristics
• Maintain correct viscosity

– Free flowing at all temperatures

• High boiling point

– Remains liquid at highest system operating

temperature

• Noncorrosive

– Does not attack metal or rubber brake system parts

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Brake Fluid (Cont.)

• Water tolerant

– Absorbs moisture collecting in system

• Lubricates

– Reduces wear of pistons and cups

• Low freezing point

– Does not freeze in cold weather

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© Goodheart-Willcox Co., Inc.

Brake Lines and Hoses

• Transfer fluid pressure from master cylinder to

wheel brake assemblies

• Brake lines are made of double-wall steel tubing

and usually have double-lap flares on their ends to
prevent high pressure leakage

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© Goodheart-Willcox Co., Inc.

Brake Lines and Hoses (Cont.)

• Brake hoses are reinforced braided rubber

hydraulic hoses with threaded metal end fittings

• Junction block is used where single brake line

must feed two wheel cylinders
– Hollow fitting with one inlet and two or more outlets

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Brake Lines and Hoses (Cont.)

• Longitudinally split brake

system
– Pistons operate front

and rear

• Diagonally split brake

system
– Pistons operate

opposite corners

(Delco)

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© Goodheart-Willcox Co., Inc.

Disc Brake Assemblies

• Friction elements are

squeezed inward to
clamp against rotating
disc, or wheel

• Disc brake assembly

consists of caliper,
brake pads, disc, and
related hardware

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© Goodheart-Willcox Co., Inc.

Brake Caliper

• Brake caliper assembly includes caliper housing,

piston, piston seal, dust boot, brake pads, special
hardware, and bleeder screw

• When brake pedal is applied, brake fluid flows into

caliper cylinder

• Piston is then pushed outward by fluid pressure,

forcing the brake pads into disc

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Brake Caliper (Cont.)

• Piston seal

– Prevents pressure leakage between piston and

cylinder

• Piston boot

– Keeps road dirt and water off caliper piston and

wall of cylinder

• Bleeder screw

– Allows air to be removed from hydraulic brake

system

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Brake Caliper (Cont.)

(Chrysler)

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Disc Brake Pads

• Steel plates to which linings are riveted or bonded
• Each caliper has inner and outer brake pad that

fits inside hydraulic brake caliper

• Brake pad linings

– Made of heat-resistant organic or semimetallic

friction material

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Disc Brake Pads (Cont.)

• Anti-rattle clips

– Keep brake pads from vibrating and rattling
– Snap onto brake pad to produce force fit in caliper

• Pad-wear sensor

– Metal tab on brake pad that informs driver of worn

brake pad linings

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© Goodheart-Willcox Co., Inc.

Brake Disc

• Brake disc or brake rotor

– Uses friction from brake pads to slow or stop wheel

rotation

• Normally made of cast iron
• May be integral part of wheel hub

– In many front-wheel-drive vehicles, disc and hub

are separate units

• May be solid or ventilated

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Disc Brake Types

• Floating caliper disc brake

– Mounted on two bolts supported by rubber

bushings

– This one-piston caliper is free to shift, or float, in

rubber bushings

• Sliding caliper disc brake

– One-piston caliper that is mounted in slots

machined in caliper adapter

– Caliper is free to slide sideways in slots or grooves

as linings wear

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Disc Brake Types

• Fixed caliper disc brake

– Uses more than one piston and caliper cylinder
– The caliper is bolted directly to the steering knuckle

• It is not free to move in relation to the disc

– Severe vibrations can occur with a slight runout of

the disc

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Disc Brake Assembly

(Chrysler and Toyota)

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Drum Brake Assemblies

• Drum brakes

– Have large drum that surrounds brake shoes and

hydraulic wheel cylinder

• Drum brake assembly consists of backing plate,

wheel cylinder, brake shoes and linings, retracting
springs, hold-down springs, brake drum, and
automatic adjusting mechanism

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Drum Brake Assembly

(Chrysler and Toyota)

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Backing Plate

• Brake backing plate

– Holds shoes, springs, wheel cylinder, and other

parts inside brake drum

• Helps keep road dirt and water off brakes
• Backing plate bolts to axle housing or spindle

support

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© Goodheart-Willcox Co., Inc.

Wheel Cylinder Assembly

• Wheel cylinder

– Consists of cylinder or housing, expander spring,

rubber cups, pistons, dust boots, and bleeder
screw

• Wheel cylinder housing

– Forms enclosure for other parts of assembly

• Wheel cylinder boots

– Keeps road dirt and water out of cylinder

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Wheel Cylinder Assembly (Cont.)

• Wheel cylinder pistons

– Metal or plastic plungers transfer force out of wheel

cylinder assembly

• Wheel cylinder cups

– Rubber seals that keep fluid from leaking past

pistons

• Wheel cylinder spring

– Helps hold rubber cups against pistons when wheel

cylinder assembly is not pressurized

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Wheel Cylinder Assembly (Cont.)

• Cup expanders

– Press outer edges of cups against wall of wheel

cylinder

• Bleeder screw

– Provides means of removing air from brake system
– Threads into hole in back of wheel cylinder

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Drum Brake Shoes

• Drum brake shoe assemblies or brake shoes

– Rub against revolving brake drum to produce

braking action

• Primary brake shoe

– Front shoe, it has slightly shorter lining than

secondary shoe

• Secondary brake shoe

– Rear shoe, it has largest lining surface area

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Retracting Springs and Hold-Down Springs

• Retracting springs

– Pull brake shoes away from brake drums when

brake pedal is released

• Hold-down springs

– Hold brake shoes against backing plate when

brakes are in released position

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Brake Shoe Adjusters

• Brake shoe adjusters

– Maintain correct drum-to-lining clearance as brake

linings wear

• Many vehicles use star wheel-type brake shoe

adjusting mechanism
– Adjusting screw assembly

• Other vehicles use latch-type adjusters
• Automatic brake shoe adjusters function when

brakes are applied with vehicle moving in reverse

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Brake Drums

• Provide rubbing surface

for brake shoe linings

• Fits over wheel lug studs
• Large hole in middle of

drum centers drum on
front hub or rear axle
flange

• Wheel and drum turn as

unit

(Ford)

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Brake Shoe Energization

• When brake shoes are

forced against rotating
drum, they are pulled
away from their pivot
point by friction

• This self-energizing

action draws shoes
tighter against drum

(EIS)

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Brake Shoe Energization (Cont.)

• With most drum brake

designs, shoe
energization is
supplemented by servo
action

• Servo action results

when primary (front)
shoe helps apply
secondary (rear) shoe

(EIS)

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Brake System Switches

Three types of switches
• Stoplight switch
• Brake warning light switch
• Low-fluid warning light switch

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Brake System Switches (Cont.)

• Stoplight switch

– Spring-loaded electrical switch that operates rear

brake lights of vehicle

• Brake warning light switch or pressure differential

valve
– Warns driver of pressure loss on one side of dual

brake system

• Low-fluid warning light switch

– Turns on dash light if brake fluid in master cylinder

becomes low

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Brake System Control Valves

• Metering valve

– Designed to equalize braking action at each wheel

during light brake applications

• Proportioning valve

– Used to equalize braking action in systems with

front disc brakes and rear drum brakes

• Combination valve

– Single unit that functions as brake warning light

switch, metering valve, and/or proportioning valve

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Parking Brakes

• Parking brakes or emergency brakes

– Provide mechanical means of applying brakes

• Cable and levers

• Electric parking brake

– Uses brake system control module to operate

electric servo motor that mechanically engages rear
brakes

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Parking Brakes (Cont.)

(Toyota)

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Parking Brakes (Cont.)

(Chrysler and Ford)

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Hybrid Brakes

• Today’s hybrid vehicles are equipped with

regenerative braking systems

• Electric braking systems
• Work with conventional hydraulic brakes to slow

vehicle and generate electricity to recharge
vehicle’s HV battery at the same time