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Chapter 7 PowerPoint Presentation

Chapter 7

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Chapter 7

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  1. Chapter 7 Disc Brake Fundamentals and Service

  2. Introduction • Disc brakes have been in use since the 1970s on the front wheels. • Now many new vehicles have disc brakes on all four wheels.

  3. Disc Brake Advantages • Light weight. • Dissipate heat better than drums. • Brake dust is not trapped. • Less prone to pull. • Self-adjusting.

  4. SELF ADJUSTING

  5. MORE ON SELF ADJUSTING

  6. Disc Brake Disadvantages • Noisier than drum brakes. • Disc brakes are not as effective as a parking brake.

  7. Internal Drum parking brake

  8. Parking brake mechanism integral to caliper.

  9. Wear Indicators • Audible – tab mounted on brake pad that contacts the disc and makes noise when wear becomes excessive. • Electronic – sensor or simple electrical contact with disc when wear is excessive • Tactile – contact with metal backing plate causes a pedal pulsation.

  10. AUDIBLE WEAR INDICATORS

  11. Electronic Wear Indicators

  12. Fixed Calipers • Caliper does not move on application. • Pistons are on both sides of caliper. • No longer installed.

  13. Floating Calipers • Also called a sliding caliper • Brake piston only located on inboard side of the caliper. • Caliper must be able to slide to engage pad on outboard side.

  14. Fixed and Floating Calipers Compared

  15. Caliper Variations • Pin • Center Abutment • Pivot pin

  16. Pin Type Caliper

  17. Center Abutment Type Caliper

  18. Pivot Pin Type Caliper

  19. Four-Wheel Disc Brake • Same basic design on rear brake calipers as front. • Provision has to be made for parking brakes. • First used on American cars in 1965 on the Corvette

  20. Road Test • Check fluid level and pedal height before driving. • Drive in a deserted area. • Make note of pulls, pulsations, and noises that may help diagnosis.

  21. Disc Brake Inspection • Check the thickness of pad material. • Check for uneven wear. • Make certain caliper slides are operational. • Check for heat damage and cracks.

  22. Rotor Inspection • Check for visual wear and heat damage. • Ensure rotor is within thickness specification. • Check for excessive runout.

  23. Rotor Inspection – Minimum Thickness

  24. Rotor Inspection – Run-out

  25. Is machining always necessary • Rotors do not have to be machined if • They are not worn beyond the manufacturers specified limits. • They do not have excessive runout. • If rotors are re-used: • Insure that BOTH the rotors on the axle do not need to be machined. • Note: Used rotors may actually have better braking function that new/machined rotors.

  26. Replacing Front Disc Linings • Usually necessary to remove calipers. • Pay attention to mountings and ant-irattle clips for reinstallation. • Loosen the bleeder screw and retract the piston. • Make sure caliper slides are clean. • Replace pads.

  27. Rear Disc Linings Rear lining replacement is similar to front except: • Most rear disc brakes have a special procedure to retract the piston due to the parking brake. Consult service literature.

  28. Special tool for retracting piston on parking brake equipped piston.

  29. Disc Caliper Rebuilding • Disc brake calipers can be rebuilt. • May be more cost-effective to replace, especially on rear. • See the text for details on caliper rebuilding.

  30. Noise Prevention • Make sure the pad fits tight in the mounting. • Ensure shims and clips are installed. • Aftermarket insulator materials may help.

  31. Installing Caliper • Install caliper to proper torque. • Make sure caliper slides are clean and lubricated. • Torque wheels to specification. • Be sure to apply brakes to seat linings before driving.

  32. Disc Brake Noise • Glazed linings • Hard spots on rotors • Not cleaning rotors after machining

  33. Pedal Pulsation • Rotor has excessive runout or thickness variation. • Improper or uneven torque on wheels. • Loose wheel bearing.

  34. Brake Pull/Uneven Wear • Sticking caliper piston • Defective brake hose • Caliper slides not free

  35. Test Drive after Brake Service • Make certain to test drive thoroughly. • Use proper procedure to “break in” linings.