1. Brake Fundamentals and Repair
Chapter 57

2. Objectives
Explain the basic principles of braking, including friction, pressure, and heat dissipation
Describe hydraulic system operation, including master cylinder, control valves, and safety switches
Understand the operation of power brakes
Diagnose and repair braking systems

3. Brake Safety Brake linings may contain Asbestos Components maybe
Hot!!!
Brakes may be held
together with springs
Thing may be spinning

4. Intro Automotive Brakes
When a car is moving, it has kinetic energy (inertia)
Brakes uses friction to stop, or hold the vehicle
Brakes convert mechanical (moving) energy into heat
Up to 600 degrees

5. Intro cont. Coefficient of friction varies with:
Temperature
Rubbing speed
Condition of surfaces
During stop, vehicle weight shifts to front brakes
Up to 80%

6. Brake system layout

7. Systems ID -Front/rear split found on rear-wheel-drive vehicles
Diagonal split found on
FWD and high front-to-rear
brake ratio
Vehicles with ABS each
wheel can have its own
circuit

8. Disc Brakes Caliper – applies the brakes using hydraulic pressure
Brake pads- contact the inboard and outboard of the rotor
Rotors- a disc that connects to the hub, used to stop the wheel

9. Brake Linings Linings are bonded or riveted backing plate
Semimetallic – sponge iron
and steel fibers
Metallic – heavy-duty and
racing conditions
Ceramic – ceramic and copper
fibers to control heat

10. Rotor parts ID Inboard surface – pad surface
Rotor hat – is the metal that connects the flange to the rotor
Mounting flange – slides on or bolts to the hub

11. Rotor parts ID cont. Hub rotors – contains bearing races
Captured rotors – bolt the back of the hub

12. Rotor Design Vented rotors - Found on the front and rear brakes
- Vents help circulate air to dissipates heat better
- Found on the front
and rear brakes
Non vented rotors
Used mostly on rears
Light duty applications

13. Measuring rotors Measure the thickness of the rotor
Measure the lateral runout of the rotor

14. Spec Sheet FRONT REAR Maximum lateral runout 0.003 in
Thickness Variation in
Maximum Scoring in
Discard Thickness in
Minimum Rotor Thickness in
New Rotor Thickness in
REAR
Rotor Discard Thickness in
Minimum Rotor Thickness in
New Rotor Thickness in

15. Brake calipers Applied by hydraulic pressure
Squeeze the pads onto the rotor
Self adjusting

16. Brake caliper parts ID

17. Caliper seal design Square cut seal
Pulls the piston back after applied
Allows the piston to self adjust
Keeps fluid in the caliper

18. Floating caliper Caliper body slides on sliders
Has 1 or 2 pistons only on one side
Light to moderate braking force

19. Non Floating Caliper Has 4 pistons or more
Equal number of pistons per side
Used for moderate to heavy braking
Pistons provide the movement

20. Measuring brake pads
Can be measured with a caliper or a plastic gauge.
Wear indicators alert the drive of excessive wear.

21. Machining Brake rotors
On car Brake lathes
Bench Brake lathes

22. Drum Brakes Braking system is enclosed Found on rear axles
Great initial stopping power

24. Drum Brake types Leading – trailing - Anchor on bottom Duo servo
-Anchor on top

25. Drum brake components Brake shoes - Friction material are
riveted or bonded
steel plate
- Friction material can
range in length

26. - Higher position better action - lower position for noise prevention
On most dual-servo brake primary shoes, the lining is positioned near the center of the lining table. Higher or lower lining positions provide better braking action, or prevent noise, in certain applications.
Shoe lining position
- Higher position better
action
- lower position for noise
prevention

27. Components cont. Lining Material’s
Semi-metallic – sponge iron and steel fibers
Metallic – heavy-duty and
racing conditions
Ceramic – ceramic and copper fibers to control heat

28. Component cont. Lining codes in three groups
- 1st manufacture name and code
- 2nd is the friction code “cold”
- 3rd is the friction code “hot”

29. Friction chart
These codes were established by the SAE (Society of Automotive Engineers): Code C 0.00 to 0.15 Code D 0.15 to 0.25 Code E 0.25 to 0.35 Code F 0.35 to 0.45 Code G 0.45 to Code H and above Code Z un-graded

30. Backing plate All components attach to it “except drum”
Mounts to the axle
Brakes apply against it

31. component cont. Hold down springs - varies in shape
- compression spring
- uses pins through the backing plate
- uses small retainers
- parts get fatigued

32. Components cont Return spring - various lengths - various tensions
- retracts shoes back to the rest position
- High tension

33. Components cont. Uni-spring - Found on leading-trailing systems
- Connects to the anchor on the backing plate
- is a hold-down and return spring

34. Component cont. Adjusters - composites for shoe wear
- attaches to both shoes
- Are know for
seizing

35. Duo servo adjusters linkage
Cable type
- runs along secondary shoe
- attaches from anchor to the adjuster pawl
- adjusts when brakes are released

36. Duo servo adjusters linkage
lever type
- runs along secondary shoe
- pivots on hold down pin
- adjusts when brakes are applied

37. Leading trailing adjuster linkage
Leading adjuster pawl
- Arm attaches on primary shoe
- adjusts when brakes are applied
- uses a designated spring

38. Leading trailing adjuster linkage
Trailing adjuster pawl
- Arm is located on secondary shoe
- adjusts when brakes are released
- uses return spring

39. Wheel cylinders Applies the rear shoes equally
Cups are usually the reason of failure
Bleeder must be installed on top
Secured by bolts or clips

40. Brake hose Provides flexibility for suspension system
Consists of hard plastic line wrapped woven fabric and rubber
Failures-
- dry cracked
- clasps internally
- internal leak causing a bubble

41. Banjo Bolt The bolt is hollow Seals with copper washers
Washers should not be reused
Bolts break easily

42. Brake Lines
Transfer fluid pressure from the master cylinder to the wheel brake assemblies
Lines
made of double wall steel tubing
made of seamless construction
tubing ends usually have double-lap flares or bubble flares

43. There are two types of double-walled tubing: Seamless Multiple ply

44. All double-walled brake tubing is plated with tin, zinc, or other similar substances for protection against rust and corrosion. CAUTION: Copper tubing should never be used for brake lines. Copper tends to burst at a lower pressure than steel.

45. All steel brake lines have one of two basic types of ends: Double Flare.

46. ISO, International Standards Organization (also called a ball flare or bubble flare).

47. Combination Valve Multiple functions in one Assembly
designs depend on braking
demands
modern vehicle the these
valves incorporated in the
EBCM

48. Metering valve Found on front disc and rear drum vehicles
Allows the rear brakes engage before front
Overcomes drum return spring pressure
Allows for more stable braking

49. Warning system Uses a spool valve between the front and rear circuits
Valve will move to side with the lowest pressure
When moved grounds the switch and turns on the warning light
Must be reset before bleeding

50. Proportioning valve Front to rear split system
Limits the rear brake applying pressure.
Uses a spring and stem valve

51. Master Cylinders

52. Master cylinders types
Front to rear split
Two ports
Found in trucks larger cars
Diagonal split
Four ports
Found in FWD cars
If front circuit fails, rears are not adequate

53. Master Cylinder Reservoirs

54. Reservoir, Housing can by plastic or casted Fluid level sensor
Reservoir seals
Vented between the cap and seal to allow fluid level change

55. Fluid Ports

56. Brakes unapplied

57. Brakes applied Primary cup seal slides over vent port
Pressure builds in primary and pushes secondary
Secondary slides forward blocking vent port
Secondary builds pressure

58. Quick take-up master cylinders
Introduced in newer vehicles
Gives the ability to use low drag calipers
Made of aluminum or composite material

59. At 70 to 100 psi, the check ball valve in the quick take-up valve allows fluid to return to the brake fluid reservoir. Because the quick take-up "works" until 100 psi is reached, a metering valve is not required to hold back the fluid pressure to the front brakes.

62. Master cylinder failures
Fluid leak from push rod end
Seal failure
Level sensor failure
Inability to bleed brakes
Push rod length
Valve position

63. PASCAL'S LAW The hydraulic principles that permit a brake system to function were discovered by a French physicist, Blaise Pascal ( ). Pascal’s Law states that "when force is applied to a liquid confined in a container or an enclosure, the pressure is transmitted equal and undiminished in every direction.“ Since this force measured in pounds (lb.) or Newtons (N) is applied to a piston with an area measured in square inches, the pressure is the force divided by the area or "10 pounds per square inch" (psi). It is this "pressure" that is transmitted, without loss, throughout the entire hydraulic system.

64. In the simple brake system, the pedal and linkage apply a 100-pound force on a master cylinder piston with an area of 1 square inch.

65. MASTER CYLINDER OPERATION Brake pedal movement and force are transferred to the brake fluid and directed to wheel cylinders or calipers.

66. Vacuum Brake Boosters

68. Vacuum boosters
Uses vacuum from the engine or
a vacuum pump
Most common type of assist unit
when applied can produce 200
to 300 psi

69. Brakes unapplied Air valve in back position Allows vacuum
to enter primary
section
vacuum control
port closed to
atmosphere 69

70. Brakes applied Air valve blocks vacuum passage vacuum control
port (opens)
Atmospheric
pressure enters
primary side
Floating control
valve and reaction
disk bleed off
pressure to stabilize 70

71. Vacuum booster tests and failures
Engine off reserve assist
3 to 4 brake depressed
- check valve
Pump the booster then start
engine, pedal should drop
No brake assist, engine idea
rises or lowers w/ depressed
- loud hissing noise
engine sucking in brake fluid

72. Power Master Power Brake Unit
Nitrogen charged
Electric 12V pump
Accumulator contains
510 to 685 psi
Pressure sensor turns
pump on

73. Power Master Diagnosis
Pressure gauge inline of
pressure sensor
No residual pressure after
long period of time
NEVER TAKE APART A
POWER MASTER UNIT!!!

74. HYDRO-BOOST HYDRAULIC BRAKE BOOSTER

75. Unapplied fluid flow Hydraulic pressure enters
the spool valve then out
to steering gear
Spool valve is in the rest
position
passage to power
chamber is closed

76. Brake pedal depressed Spool valve moved Blocks off return line passage
Fluid flows through the spool valve
Pressure builds behind the power piston
Reaction rod controls the apply pressure

77. Accumulator Fills during the brake apply
Caution large spring internally
Contains residual pressure in case of engine failure

78. Hydro boost testing No steering or brake assist. “pump concern”
Fluid level
Fluid leaks
Internal assist unit

79. Emergency Brakes
Appling Mechanism

80. Cable system One cable comes from handle
Equalizer makes both rear apply equally
E-brakes are always going to the rear
All assemblies have a tread adjuster

81. Drum brake –E-brake mech.
Cable secures to backing plate
Pulls on parking brake lever
Lever pivots on shoe
Strut travels from lever to other shoe

82. E- brake drum w/rear disc
Uses the hat of the rotor as the drum
Small shoes internally
Applies mechanically

83. Caliper E- brake systems
Cable connects to a back of the calper