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Disc Brake System Diagnosis

WARNING: This page is about a different car, the 2003 GMC Safari and 2003 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
  1. Were you sent here from a Brake Symptom List? If so, go to next step. If not, go to GENERAL DIAGNOSIS (HYDRAULIC BRAKES) .
  2. Visually inspect the disc brake pads for the following:
    • Lining thickness
    • Uneven and/or abnormal wear (edge-to-edge and/or side-to-side)
    • Evidence of contamination from an external substance
    • Looseness or damage (including pad hardware)
    Did you find any conditions to indicate a concern with any of the disc brake pads? If so, go to next step. If not, go to step  12.
  3. Are any of the disc brake pads contaminated? If not, go to step  8. If so, go to next step.
  4. Are any of the disc brake pads worn unevenly? If not, go to step  7. If so, go to next step.
  5. Are any of the disc brake pads and/or pad hardware loose or damaged? If not, go to step  7. If so, go to next step.
  6. Remove and inspect the worn disc brake pads for glazing, looseness, heat spots or damage. Replace worn disc brake pads as a complete axle set. See FRONT BRAKE PADS  or REAR BRAKE PADS  under REMOVAL & INSTALLATION. After completing repair, go to step  12.
    • Remove appropriate disc brake calipers and support calipers. Do not disconnect hydraulic brake flex hoses from calipers. See BRAKE CALIPER (FRONT)  or BRAKE CALIPER (REAR)  under REMOVAL & INSTALLATION.
    • Inspect the disc brake caliper mounting/sliding hardware for the following conditions:
      1. Loose, bent, cracked, or damaged steering knuckle
      2. Binding or seized hardware
      3. Worn, damaged or missing hardware components
    • Replace components as required.
    • Replace unevenly-worn, loose or damaged disc brake pads as a complete axle set. See FRONT BRAKE PADS  or REAR BRAKE PADS  under REMOVAL & INSTALLATION.
    After completing repairs, go to step  12.
  8. Inspect the disc brake calipers, brake hoses and brake pipes for evidence of an external brake fluid leak. Replace any components found to be leaking brake fluid. Refer to the following procedures as required: Did you find and correct the source of the leak causing contamination of the pads? If so, go to step  11. If not, go to next step.
  9. Inspect the wheel drive shaft outer seals (boots), if equipped, for damage and evidence of a grease leak. Replace any wheel drive shaft seal (boot) that is found to be leaking grease which may be the source of the contamination to the pads. See appropriate AXLE SHAFTS article. Did you find and correct the source of the leak causing contamination of the pads? If so, go to step  11. If not, go to next step.
  10. Inspect engine, transmission and power steering for damage and evidence of an external fluid leak. Replace or repair any components found to be leaking fluid which may be the source of the contamination to the pads. After repairs, go to next step.
    • Clean the remaining disc brake system components to remove any traces of the contaminant.
    • Remove disc brake calipers (as appropriate) from the steering knuckles and support the calipers. Do not disconnect the hydraulic brake flex hoses from the calipers. See FRONT BRAKE CALIPER  under REMOVAL & INSTALLATION.
    • Inspect the disc brake caliper mounting/sliding hardware for binding or seized hardware. Inspect for distorted, worn, damaged or missing hardware components. See DISC BRAKE HARDWARE (FRONT)  or DISC BRAKE HARDWARE (REAR)  under REMOVAL & INSTALLATION.
    • Replace the caliper mounting/sliding hardware components as required. See DISC BRAKE HARDWARE (FRONT)  or DISC BRAKE HARDWARE (REAR)  under REMOVAL & INSTALLATION.
    • Replace contaminated disc brake pads as a complete axle set. See FRONT BRAKE PADS  under REMOVAL & INSTALLATION. After repairs, go to next step.
  12. Visually inspect each of the disc brake rotor shields/backing plates for evidence of contact with the brake rotors. Are any of the brake rotor shields/backing plates contacting the brake rotors? If so, go to next step. If not, go to step  14.
  13. Repair or replace the disc brake rotor shields/backing plates as required. See DISC BRAKE SPLASH SHIELD . After completing repair, go to next step.
  14. Check the thickness of each of the disc brake rotors. Make a determination for each brake rotor if the rotor can be REFINISHED and REMAIN ABOVE the minimum requirements. Does the disc brake rotor meet the minimum requirements for REFINISHING? If so, go to next step. If not, go to step  17
  15. Inspect each of the disc brake rotors for the following surface and wear conditions:
    • Heavy rust and/or pitting.
    • Cracks and/or heat spots.
    • Excessive blueing discoloration.
    Inspect braking surface wear for the following conditions:
    • Deep or excessive scoring beyond maximum acceptable level.
    • Lateral runout beyond maximum acceptable level.
    • Thickness variation beyond maximum acceptable level.
    Make a determination for each brake rotor if the rotor requires refinishing based upon the results of the inspection. If the brake rotor exhibits any of the following conditions, it requires refinishing.
    • Rotor exhibits one or more of the braking surface conditions.
    • Rotor is beyond the acceptable level in one or more of the braking surface wear conditions.
    Does the brake rotor require REFINISHING? If so, go to next step. If not, go to step  20.
  16. Refinish the brake rotor. Inspect the brake rotor thickness. Were you able to REFINISH the brake rotor within the minimum requirements? If so, go to step  20. If not, go to step  19.
  17. Is the brake rotor at or below the DISCARD requirements? If so, go to step  19. If not, go to next step.
  18. Inspect each of the disc brake rotors for the following surface and wear conditions:
    • Heavy rust and/or pitting.
    • Cracks and/or heat spots.
    • Excessive blueing discoloration.
    Braking Surface Wear Conditions:
    • Deep or excessive scoring beyond maximum acceptable level.
    • Lateral runout beyond maximum acceptable level.
    • Thickness variation beyond maximum acceptable level.
    Make a determination for each brake rotor if the rotor requires refinishing based upon the results of the inspection. If the brake rotor exhibits any of the following conditions, it requires refinishing.
    • Rotor exhibits one or more of the braking surface conditions.
    • Rotor is beyond the acceptable level in one or more of the braking surface wear conditions.
    Does the brake rotor require REPLACEMENT? If so, go to next step. If not, go to step  20.
  19. Replace brake rotor. See FRONT BRAKE ROTOR  under REMOVAL & INSTALLATION. After completing replacement, go to next step.
  20. Install or connect components that were removed or disconnected during diagnosis.
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