Modern Automotive Technology

© Goodheart-Willcox Co., Inc.

by

Russell Krick

Publisher

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



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


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



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


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


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


Drum and Disc Brakes

Disc brakes Drum brakes


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


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


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


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


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



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

small amount of movement



Hydraulic jack operation


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


Hydraulic Brake Action



Brake Pedal Assembly

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


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


Master Cylinder

Brakes applied Brakes released


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



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



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


Piston and Cup


Residual Pressure

ValveBrakes applied, fluid

flows freely

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

master cylinder


Dual Master Cylinder


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


Dual Master

Cylinder


Dual Master Cylinder(Normal Operation)

Both pistons produce pressure to all four wheel brake assemblies


Dual Master Cylinder(Rear Brake Circuit Leak)

Primary piston pushes on thesecondary piston, two wheel brake

assemblies still work


Dual Master Cylinder(Front Brake Circuit Leak)

Secondary piston slides forward,primary piston operates two

wheel brakes normally


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)


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

Brake Fluid


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


Brake Lines and Hoses


Brake Line Hardware

Brackets and clips secure the hoses and lines

to prevent damage


Brake Systems

Often used on rear-wheel-drive vehicles

Often used on front-wheel-drive vehicles,

with high front to rear brake ratio


Disc Brake Assembly

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


Single Piston Caliper

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


Fixed Caliper

Caliper remains stationary as pistons on each side clamp the rotor


Brake Caliper Assembly


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


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


Caliper Operation

Brakes applied Brakes released


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


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


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


Disc Brake Assembly

This rotor is vented to increase cooling


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


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


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


Drum Brake Assembly

Large drum surrounds the brake shoes and the hydraulic wheel cylinder


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


Wheel Cylinder Assembly

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


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


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


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


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


Drum Brake Assembly


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


Brake Shoe Adjusters

Cable-type star wheel adjuster



Link-type star wheel adjuster



Lever-type star wheel adjuster



Cable-type star wheel adjuster with an overtravel spring



Lever-latch adjuster



Sliding-latch adjuster


Brake Drums

Provide a rubbing surface forthe brake shoe linings


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


Brake Shoe Energization

Self-Energizing Action. Primary shoe is self-

energized

Servo Action. Less wheel cylinder hydraulic

pressure is needed to apply the brakes


Master Cylinder

Incorporates a proportioning valve and a warning light switch



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


Parking Brake

Components

Foot-operated parking brake

pedal

Lever pushes the shoes against the

drum


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


Rear Disc Brake Caliper

Note the parking brake mechanism

Documents

Modern Automotive Technology