Modern Automotive Technology

© Goodheart-Willcox Co., Inc.

by

Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.Tinley Park, Illinois

© Goodheart-Willcox Co., Inc.

© Goodheart-Willcox Co., Inc.

Basic brake system Braking ratio Brake system hydraulics Brake system components Parking brakes

© Goodheart-Willcox Co., Inc.

Automotive Brakes Provide a means of using friction to

either slow, stop, or hold the wheels of a vehicle

When a car is moving, it has energy stored in the form of inertia (kinetic energy)

To stop the vehicle, the brakes convert kinetic (moving) energy into heat

© Goodheart-Willcox Co., Inc.

© Goodheart-Willcox Co., Inc.

Brake Operation When the driver pushes on the brake

pedal, lever action pushes a rod into the brake booster and master cylinder

Pressure developed in the master cylinder forces fluid through the brake lines to the wheel brake assemblies

Brake assemblies use this pressure to cause friction for braking

© Goodheart-Willcox Co., Inc.

Parking Brake Parking brake system uses cables or

rods to mechanically apply the rear brakes

Provides a system for holding the wheels when the vehicle is parked, or stopping the vehicle during complete hydraulic brake system failure

© Goodheart-Willcox Co., Inc.

Drum and Disc Brakes Two common types of brake

assemblies: Disc brakes

often used on the front wheels

Drum brakesoften used on the rear wheels

© Goodheart-Willcox Co., Inc.

Drum and Disc Brakes

Disc brakes Drum brakes

© Goodheart-Willcox Co., Inc.

Comparison of front wheel braking effort to rear wheel braking effort

When a vehicle stops, its weight tends to transfer onto the front wheels

Rear tires lose some of their grip Front wheels must do more of the

braking

© Goodheart-Willcox Co., Inc.

Typical Braking Ratios Rear wheel drive vehicles:

front brakes may handle 60% to 70% of the braking, rear brakes handle 30% to 40%

Front wheel drive vehicles:more weight is concentrated on the front

wheelsbraking ratio is even higher at the front

wheels

© Goodheart-Willcox Co., Inc.

Automotive brakes use a hydraulic system

Hydraulic brakes use a confined brake fluid to transfer brake pedal motion and pressure to each of the wheel brake assemblies

© Goodheart-Willcox Co., Inc.

Hydraulic Principles Liquids in a confined area will not

compress When pressure is applied to a closed

system, pressure is exerted equally in all directions

Hydraulics can be used to increase or decrease force or motion

© Goodheart-Willcox Co., Inc.

Hydraulic System Action

Pressure and motion can be transferred from one cylinder to another

Cylinders of the same size:if one piston is moved, the other will move

the same amount with the same force

Cylinders of different size:if the smaller piston is moved, the larger

piston will move with more force but will move a shorter distance

© Goodheart-Willcox Co., Inc.

Hydraulic System Action

In a hydraulic jack, a small piston acts on a large piston, resulting in great force, but a

small amount of movement

© Goodheart-Willcox Co., Inc.

Hydraulic System Action

Hydraulic jack operation

© Goodheart-Willcox Co., Inc.

Hydraulic Brake Action

Master cylinder acts on the pumping piston that supplies system pressure

Wheel cylinder acts as the power piston, moving the friction linings into contact with the rotating drums or discs

© Goodheart-Willcox Co., Inc.

Hydraulic Brake Action

© Goodheart-Willcox Co., Inc.

© Goodheart-Willcox Co., Inc.

Brake Pedal Assembly

Acts as a lever to increase the force applied to the master cylinder piston

© Goodheart-Willcox Co., Inc.

Master Cylinder Foot operated pump that forces fluid to

the brake lines and wheel cylinders Develops pressure to apply the brakes Equalizes pressure required for braking Keeps the system full of fluid as the

linings wear May maintain a slight pressure to keep

contaminants from entering the system

© Goodheart-Willcox Co., Inc.

Master Cylinder

Brakes applied Brakes released

© Goodheart-Willcox Co., Inc.

Master Cylinder Components

© Goodheart-Willcox Co., Inc.

Master Cylinder Components

Cup and pistonused to pressurize the systemwhen they are pushed forward, they trap

fluid, building pressure

Intake portallows fluid to enter the rear of the

cylinder as the piston slides forwardfluid flows from the reservoir, into the area

behind the piston and cup

© Goodheart-Willcox Co., Inc.

Master Cylinder Components

Compensating portreleases pressure when the piston returns

to the released positionfluid can flow back into the reservoir

through the compensating port

Residual pressure valvesmaintain residual fluid pressure of

approximately 10 psi (69 kPa) to help keep contaminants out of the system

© Goodheart-Willcox Co., Inc.

Master Cylinder Components

Rubber bootprevents dust, dirt, and moisture from

entering the back of the master cylinder

Reservoirstores an extra supply of brake fluidcast as part of the housing or a removable

plastic part

© Goodheart-Willcox Co., Inc.

Piston and Cup

© Goodheart-Willcox Co., Inc.

Residual Pressure

ValveBrakes applied, fluid

flows freely

Brakes released, valve closes to restrict the return of fluid to the

master cylinder

© Goodheart-Willcox Co., Inc.

Dual Master Cylinder

© Goodheart-Willcox Co., Inc.

Dual Master Cylinder Uses two separate hydraulic pistons

and two fluid reservoirs Each piston operates a hydraulic circuit

that controls two wheel brake assemblies

If there is a leak in one of the hydraulic circuits, the other circuit can still provide braking action on two wheels

© Goodheart-Willcox Co., Inc.

Dual Master

Cylinder

© Goodheart-Willcox Co., Inc.

Dual Master Cylinder(Normal Operation)

Both pistons produce pressure to all four wheel brake assemblies

© Goodheart-Willcox Co., Inc.

Dual Master Cylinder(Rear Brake Circuit Leak)

Primary piston pushes on thesecondary piston, two wheel brake

assemblies still work

© Goodheart-Willcox Co., Inc.

Dual Master Cylinder(Front Brake Circuit Leak)

Secondary piston slides forward,primary piston operates two

wheel brakes normally

© Goodheart-Willcox Co., Inc.

Brake Fluid Specially blended hydraulic fluid that

transfers pressure to the wheel brake assemblies

Rated by the SAE and DOT SAE (Society of Automotive Engineers) DOT (Department of Transportation)

© Goodheart-Willcox Co., Inc.

Brake fluid must have the following characteristics:correct viscosity at all temperatureshigh boiling pointnoncorrosivewater tolerantlubricates componentslow freezing point

Brake Fluid

© Goodheart-Willcox Co., Inc.

Brake Lines and Hoses Transfer fluid pressure from the master

cylinder to the wheel brake assemblies Lines

made of double wall steel tubingtubing ends use double flare or ISO flare

Hosesmade of reinforced rubberused where flexing action is necessary

© Goodheart-Willcox Co., Inc.

Brake Lines and Hoses

© Goodheart-Willcox Co., Inc.

Brake Line Hardware

Brackets and clips secure the hoses and lines

to prevent damage

© Goodheart-Willcox Co., Inc.

Brake Systems

Often used on rear-wheel-drive vehicles

Often used on front-wheel-drive vehicles,

with high front to rear brake ratio

© Goodheart-Willcox Co., Inc.

Disc Brake Assembly

Assembly consists of a caliper, brake pads, a rotor, and hardware

© Goodheart-Willcox Co., Inc.

Single Piston Caliper

Caliper slides as the piston moves in to clamp the brake pads against the rotor

© Goodheart-Willcox Co., Inc.

Fixed Caliper

Caliper remains stationary as pistons on each side clamp the rotor

© Goodheart-Willcox Co., Inc.

Brake Caliper Assembly

© Goodheart-Willcox Co., Inc.

Caliper Components Piston seal

prevents fluid leakage between the piston and the cylinder

helps pull the piston back into the cylinder when the brakes are not applied

Bootprevents road dirt and water entry

Bleeder screwallows air to be removed from the system

© Goodheart-Willcox Co., Inc.

Caliper Operation When the brakes are applied, brake

fluid flows into the caliper cylinder Fluid pressure pushes the piston

outward, forcing the brake pads into the rotor

When the brakes are released, the stretched piston seal pulls the piston back into the bore, as fluid pressure drops

© Goodheart-Willcox Co., Inc.

Caliper Operation

Brakes applied Brakes released

© Goodheart-Willcox Co., Inc.

Disc Brake Pads Steel plates to which linings are riveted Linings

made of heat-resistant organic or semimetallic friction material

semimetallic linings withstand higher temperatures without losing their frictional properties

© Goodheart-Willcox Co., Inc.

Disc Brake Pads Anti-rattle clips

keep the brake pads from vibrating and rattling

Pad wear sensormetal tab on the brake pademits a loud squeal when it scrapes

against the brake disc when the lining has worn too thin

© Goodheart-Willcox Co., Inc.

Brake Disc (Rotor) Uses friction from the brake pads to

slow or stop wheel rotation Normally made of cast iron Constructed as part of the hub, or a

separate unit May be solid, or a ventilated rib

construction

© Goodheart-Willcox Co., Inc.

Disc Brake Assembly

This rotor is vented to increase cooling

© Goodheart-Willcox Co., Inc.

Floating Caliper

Disc brake is mounted on two bolts supported by rubber bushings

Uses one piston Caliper is free to shift, or float, in the

rubber bushings

© Goodheart-Willcox Co., Inc.

Sliding Caliper

Uses one piston Mounted in slots machined in the

caliper adapter Caliper is free to slide sideways in the

slots as the linings wear

© Goodheart-Willcox Co., Inc.

Fixed Caliper

Uses more than one piston and caliper cylinder

Caliper is bolted directly to the steering knuckle

Pistons on both sides of the disc push against the brake pads

© Goodheart-Willcox Co., Inc.

Drum Brake Assembly

Large drum surrounds the brake shoes and the hydraulic wheel cylinder

© Goodheart-Willcox Co., Inc.

Backing Plate Holds the springs, wheel cylinder, and

other parts inside the drum Helps keep road dirt and water off the

brakes Bolts to the axle housing or the spindle

support

© Goodheart-Willcox Co., Inc.

Wheel Cylinder Assembly

Uses master cylinder pressure to force the brake shoes out against the drum

© Goodheart-Willcox Co., Inc.

Wheel Cylinder Components

Bootskeep road dirt and water out of the

cylinder Pistons

metal or plastic plungers that transfer force out of the cylinder to the brake shoes

Cupsrubber seals that keep fluid from leaking

past the pistons

© Goodheart-Willcox Co., Inc.

Wheel Cylinder Components

Springshold the rubber cups against the pistons

when the wheel cylinder assembly is not pressurized

metal expanders may be used on the ends

Bleeder screwprovides a means of removing air from

the brake system

© Goodheart-Willcox Co., Inc.

Brake Shoes Rub against the revolving brake drum

to produce braking action Made by fastening organic friction

material onto a metal shoerivets or bonding agents may be used

Primary shoe is the front shoeuses the shortest lining

Secondary shoe is the rear shoeuses the largest lining surface area

© Goodheart-Willcox Co., Inc.

Brake Shoes Retracting springs

pull the brake shoes away from the brake drums when the brake pedal is released

Hold-down springshold the brake shoes against the backing

plate when the brakes are in the released position

© Goodheart-Willcox Co., Inc.

Drum Brake Assembly

© Goodheart-Willcox Co., Inc.

Brake Shoe Adjusters Maintain the correct drum-to-lining

clearance as the brake linings wear Automatic adjusters normally function

when the brakes are applied with the vehicle moving in reverse

If there is too much lining clearance, the brake shoes move outward and rotate with the drum enough to operate the adjuster lever

© Goodheart-Willcox Co., Inc.

Brake Shoe Adjusters

Cable-type star wheel adjuster

© Goodheart-Willcox Co., Inc.

Brake Shoe Adjusters

Link-type star wheel adjuster

© Goodheart-Willcox Co., Inc.

Brake Shoe Adjusters

Lever-type star wheel adjuster

© Goodheart-Willcox Co., Inc.

Brake Shoe Adjusters

Cable-type star wheel adjuster with an overtravel spring

© Goodheart-Willcox Co., Inc.

Brake Shoe Adjusters

Lever-latch adjuster

© Goodheart-Willcox Co., Inc.

Brake Shoe Adjusters

Sliding-latch adjuster

© Goodheart-Willcox Co., Inc.

Brake Drums

Provide a rubbing surface forthe brake shoe linings

© Goodheart-Willcox Co., Inc.

Brake Shoe Energization

When the brake shoes are forced against the rotating drum, they are pulled away from their pivot point by friction

This self-energizing action draws the shoes tighter against the drum

Servo action results when the primary shoe helps apply the secondary shoe

© Goodheart-Willcox Co., Inc.

Brake Shoe Energization

Self-Energizing Action. Primary shoe is self-

energized

Servo Action. Less wheel cylinder hydraulic

pressure is needed to apply the brakes

© Goodheart-Willcox Co., Inc.

Master Cylinder

Incorporates a proportioning valve and a warning light switch

© Goodheart-Willcox Co., Inc.

© Goodheart-Willcox Co., Inc.

Parking Brake Operation

When the hand or foot lever is activated, it pulls a steel cable that runs through a housing

Cable movement pulls on a lever inside the drum or disc brake assembly, forcing the brake linings against the rear drums or discs

© Goodheart-Willcox Co., Inc.

Parking Brake

Components

Foot-operated parking brake

pedal

Lever pushes the shoes against the

drum

© Goodheart-Willcox Co., Inc.

Parking Brake Operation

(Rear Disc Brakes)

A thrust screw and a lever can be added to the brake caliper

When the parking brake is applied, the cable pulls on the caliper lever

Caliper lever turns the thrust screw, which pushes on the caliper piston and applies the brake pads to the disc

© Goodheart-Willcox Co., Inc.

Rear Disc Brake Caliper

Note the parking brake mechanism