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Chapter 7

Chapter 7. Disc Brake Fundamentals and Service. 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. Disc Brake Advantages. Light weight. Dissipate heat better than drums. Brake dust is not trapped.

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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.

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