1. Modern Automotive Technology
PowerPoint for
Modern Automotive
Technology by
Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 71
Brake System
Fundamentals

3. Contents Basic brake system Braking ratio Brake system hydraulics
Brake system components
Parking brakes

4. Automotive Brakes
Provide a means of using friction to slow, stop, or hold the wheels of a vehicle
When a car is moving, it has kinetic energy (inertia)
To stop the vehicle, the brakes convert mechanical (moving) energy into heat

5. Basic Brake System

6. Brake Operation
When the driver pushes on the brake pedal, lever action pushes a rod into the brake booster and master cylinder
The pressure developed in the master cylinder forces fluid through the brake lines to the wheel brake assemblies
The brake assemblies use this pressure to cause friction for braking

7. Parking Brake
The 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 on a hill or stopping the vehicle during complete hydraulic brake system failure

8. Drum and Disc Brakes Two common types of brake assemblies: Disc brakes
often used on the front wheels
Drum brakes
often used on the rear wheels

9. Disc brakes Drum brakes
Drum and Disc Brakes
Disc brakes Drum brakes

10. Braking Ratio
Comparison of front wheel braking effort to rear wheel braking effort
When a vehicle stops, its weight tends to transfer onto the front wheels
The rear tires lose some of their grip
The front wheels must do more of the braking

11. 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 wheels
braking ratio is even higher at the front wheels

12. Brake System Hydraulics
Automotive brakes use a hydraulic system
Hydraulic brakes use confined brake fluid to transfer brake pedal motion and pressure to each of the wheel brake assemblies

13. 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

14. 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 sizes:
if the smaller piston is moved, the larger piston will move with more force, but it will move a shorter distance

15. 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

16. Hydraulic System Action
Hydraulic jack operation

17. Hydraulic Brake Action
The master cylinder acts as the pumping piston that supplies system pressure
The wheel cylinder acts as the power piston, moving the friction linings into contact with the rotating drums or discs

18. Hydraulic Brake Action

19. Brake System
Components

20. Brake Pedal Assembly
A lever arm to increase the force applied to the master cylinder piston

21. 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

22. Master Cylinder
Brakes applied
Brakes released

23. Master Cylinder Components

24. Master Cylinder Components
Cup and piston
used to pressurize the system
when they are pushed forward, they trap fluid, building pressure
Intake port
allows fluid to enter the rear of the cylinder as the piston slides forward
fluid flows from the reservoir, into the area behind the piston and cup

25. Master Cylinder Components
Compensating port
releases pressure when the piston returns to the released position
fluid can flow back into the reservoir through the compensating port
Residual pressure valves
maintain residual fluid pressure of approximately 10 psi (69 kPa) to help keep contaminants out of the system

26. Master Cylinder Components
Rubber boot
prevents dust, dirt, and moisture from entering the back of the master cylinder
Reservoir
stores an extra supply of brake fluid
cast as part of the housing or added as a removable plastic part

27. Piston and Cup

28. Residual Pressure Valve
Brakes applied, fluid flows freely
Brakes released, the valve closes to restrict the return of fluid to the master cylinder

29. Dual Master Cylinder

30. 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

31. Dual Master Cylinder

32. Dual Master Cylinder (Normal Operation)
Both pistons produce pressure to all four wheel brake assemblies

33. Dual Master Cylinder (Rear Brake Circuit Leak)
Primary piston pushes on the secondary piston, two wheel brake assemblies still work

34. Dual Master Cylinder (Front Brake Circuit Leak)
Secondary piston slides forward, primary piston operates two wheel brakes normally

35. Power Brakes
Use a booster and vacuum or hydraulic pressure to assist brake pedal application
The booster is located between the brake pedal linkage and the master cylinder
When the driver presses on the brake pedal, the brake booster helps push on the master cylinder pistons

36. Vacuum Booster
Uses vacuum produced in the engine intake manifold or by a separate pump to apply the hydraulic brake system
Consists of a housing that encloses a diaphragm
When vacuum is applied to one side of the booster, the diaphragm moves toward the low-pressure area

37. Vacuum Booster Operation

38. Atmospheric Suspended Brake Booster
Atmospheric pressure is present on both sides of the diaphragm when the brakes are released
When the brakes are applied, vacuum is routed to one side of the booster
Atmospheric pressure then pushes on and moves the diaphragm

39. Vacuum Suspended Brake Booster
Vacuum is present on both sides of the diaphragm when the brakes are released
When the brakes are applied, vacuum is released from one side of the booster
Atmospheric pressure then pushes on and moves the diaphragm

40. Vacuum Brake Booster

41. Hydraulic Booster
Uses power steering pump pressure to help the driver apply the brake pedal
Known as hydro-boost or hydra-booster
Commonly used on vehicles with diesel engines
diesel engines do not produce a usable amount of intake manifold vacuum

42. Hydraulic Booster

43. Hydraulic Booster
When the pedal pushes on the unit, the spool valve allows more oil to enter the pressure chamber, pushing on the power piston

44. 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)

45. Brake Fluid Brake fluid must have the following characteristics:
correct viscosity at all temperatures
high boiling point
noncorrosive
water tolerant
lubricates components
low freezing point

46. Brake Lines and Hoses
Transfer fluid pressure from the master cylinder to the wheel brake assemblies
Lines
made of double-wall steel tubing
tubing ends usually have double-lap flares
Hoses
made of reinforced rubber
used where flexing action is necessary

47. Brake Lines and Hoses

48. Brackets and clips secure the hoses and lines to prevent damage
Brake Line Hardware
Brackets and clips secure the hoses and lines to prevent damage

49. Brake Systems Often used on rear-wheel-drive vehicles
Often used on front-wheel-drive vehicles, with high front-to-rear brake ratio

50. The assembly consists of a caliper, brake pads, a rotor, and hardware
Disc Brake Assembly
The assembly consists of a caliper, brake pads, a rotor, and hardware

51. Single-Piston Caliper
The caliper slides, as the piston moves in to clamp the brake pads against the rotor

52. Fixed Caliper
The caliper remains stationary, as pistons on each side clamp the rotor

53. Brake Caliper Assembly

54. Caliper Components Piston seal Boot Bleeder screw
prevents pressure leakage between the piston and the cylinder
helps pull the piston back into the cylinder when the brakes are not applied
Boot
prevents road dirt and water entry
Bleeder screw
allows air to be removed from the system

55. 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

56. Brakes applied Brakes released
Caliper Operation
Brakes applied Brakes released

57. 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

58. Disc Brake Pads Anti-rattle clips Pad-wear sensor
keep the brake pads from vibrating and rattling
Pad-wear sensor
metal tab on the brake pad
emits a loud squeal when it scrapes against the brake disc, which happens when the lining has worn too thin

59. 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 as a separate unit
Can be solid or have a ventilated rib construction

60. This rotor is vented to increase cooling
Disc Brake Assembly
This rotor is vented to increase cooling

61. Floating Caliper
The disc brake is mounted on two bolts supported by rubber bushings
Uses one piston
The caliper is free to shift, or float, in the rubber bushings

62. Sliding Caliper Uses one piston
Mounted in slots machined in the caliper adapter
The caliper is free to slide sideways in the slots as the linings wear

63. Fixed Caliper Uses more than one piston and caliper cylinder
The caliper is bolted directly to the steering knuckle
Pistons on both sides of the disc push against the brake pads

64. Drum Brake Assembly
A large drum surrounds the brake shoes and the hydraulic wheel cylinder

65. 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

66. Wheel Cylinder Assembly
Uses master cylinder pressure to force the brake shoes out against the drum

67. Wheel Cylinder Components
Boots
keep road dirt and water out of the cylinder
Pistons
metal or plastic plungers that transfer force out of the cylinder to the brake shoes
Cups
rubber seals that keep fluid from leaking past the pistons

68. Wheel Cylinder Components
Springs
hold the rubber cups against the pistons when the wheel cylinder assembly is not pressurized
metal expanders may be used on the ends
Bleeder screw
provides a means of removing air from the brake system

69. Brake Shoes
Rub against the revolving brake drum to produce braking action
Made by fastening organic friction material onto a metal shoe
rivets or bonding agents may be used
The front shoe is the primary shoe
uses the shorter lining
The rear shoe is the secondary shoe
uses the larger lining surface area

70. Brake Shoes Retracting springs Hold-down springs
pull the brake shoes away from the brake drums when the brake pedal is released
Hold-down springs
hold the brake shoes against the backing plate when the brakes are in the released position

71. Drum Brake Assembly

72. 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 adjusting lever

73. Cable-type star wheel adjuster
Brake Shoe Adjusters
Cable-type star wheel adjuster

74. Link-type star wheel adjuster
Brake Shoe Adjusters
Link-type star wheel adjuster

75. Lever-type star wheel adjuster
Brake Shoe Adjusters
Lever-type star wheel adjuster

76. Cable-type star wheel adjuster with an overtravel spring
Brake Shoe Adjusters
Cable-type star wheel adjuster with an overtravel spring

77. Brake Shoe Adjusters
Lever-latch adjuster

78. Sliding-latch adjuster
Brake Shoe Adjusters
Sliding-latch adjuster

79. Provide a rubbing surface for the brake shoe linings
Brake Drums
Provide a rubbing surface for the brake shoe linings

80. 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

81. Brake Shoe Energization
Self-Energizing Action
Non-Servo Action
Primary shoe is self-energized
Servo Action
Less hydraulic pressure is needed to apply the brakes

82. Control Valves and Switches

83. Stoplight Switch Operates the rear brake lights
Normally open switch, usually mounted on the brake pedal mechanism
When the brake pedal is pressed, it closes the switch

84. Brake Warning Light Switch
Also called the pressure differential valve
Warns the driver of a pressure loss on one side of a dual brake system
If a leak develops in either the primary or secondary brake system, unequal pressure pushes the switch piston to one side, grounding the indicator circuit

85. Brake Warning Light Circuit

86. Brake Warning Light Switch
Pressure difference pushes the piston to close the warning lamp circuit

87. Low-Fluid Warning Light Switch
Turns on a dash light if the brake fluid in the master cylinder becomes low
Often mounts in the master cylinder lid or cover
Commonly operated by a float

88. Metering Valve
Used to equalize braking action on vehicles with front-wheel disc brakes and rear-wheel drum brakes
Located in the line to the disc brakes
Prevents the front brakes from applying until pressure reaches approximately 75–135 psi (517–930 kPa)
This pressure overcomes the rear brake return springs

89. Proportioning Valve
Used to equalize braking action on vehicles with front-wheel disc brakes and rear-wheel drum brakes
Located in the line to the drum brakes
Limits pressure at the rear drum brakes when high pressure is needed to apply the front disc brakes
Minimizes rear-wheel lockup during heavy braking

90. Combination Valve
Single unit that functions as a brake warning light switch, a metering valve, and/or a proportioning valve
Common on late-model vehicles

91. Combination Valve

92. Incorporates a proportioning valve and a warning light switch
Master Cylinder
Incorporates a proportioning valve and a warning light switch

93. Parking Brakes

94. Parking Brake Operation
When the hand or foot lever is activated, it pulls a steel cable that runs through a housing
The cable pulls on a lever inside the drum or disc brake assembly, forcing the brake linings against the rear drums or discs

95. Parking Brake Components
Foot-operated parking brake pedal
A lever pushes the shoes against the drum

96. 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
The caliper lever turns the thrust screw, which pushes on the caliper piston and applies the brake pads to the disc

97. Rear Disc Brake Caliper
Note the parking brake mechanism