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Brake Fundamentals and Repair

Brake Fundamentals and Repair. Chapter 57. 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

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Brake Fundamentals and Repair

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  1. Brake Fundamentalsand 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 - 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 Maximum lateral runout 0.003 in Thickness Variation 0.0005 in Maximum Scoring 0.060 in Discard Thickness 1.210 in Minimum Rotor Thickness 1.220 in New Rotor Thickness 1.270 in REAR Rotor Discard Thickness 0.350 in Minimum Rotor Thickness 0.390 in New Rotor Thickness 0.430 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

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

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

  25. 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

  26. 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

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

  28. These codes were established by the SAE (Society of Automotive Engineers):Code C 0.00 to 0.15Code D 0.15 to 0.25Code E 0.25 to 0.35Code F 0.35 to 0.45Code G 0.45 to 0.55 Code H 0.55 and aboveCode Z un-graded Friction chart

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

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

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

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

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

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

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

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

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

  38. 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

  39. 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

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

  41. 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

  42. There are two types of double-walled tubing:SeamlessMultiple ply

  43. 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.

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

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

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

  47. 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

  48. 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

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

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