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Disc Brake System Diagnosis

  1. If you sent here from a brake symptom test, go to step  2. If you were not sent her from a brake symptom, see HYDRAULIC BRAKE SYSTEM  under DIAGNOSTIC STARTING POINTS.
  2. Visually inspect the disc brake pads for the following conditions:
    • Lining thickness below specifications.
    • Uneven and/or abnormal wear, edge-to-edge and/or side-to-side.
    • Looseness or damage, including pad hardware.
    • Evidence of contamination from an external substance.
    If any of the conditions were found and indicated a concern with any of the front and/or rear disc brake pads, go to step  3. If any of the conditions were not found and did not cause any concern, go to step  12.
  3. If any of the front and/or rear disc brake pads are contaminated, go to step  8. If any of the front and/or rear disc brake pads are not contaminated, go to step  4.
  4. If any of the front and/or rear disc brake pads are worn unevenly, go to step  7. If any of the front and/or rear disc brake pads are not worn unevenly, go to step  5.
  5. If any of the front and/or rear disc brake pads and/or pad hardware are loose or damaged, go to step  7. If any of the front and/or rear disc brake pads and/or pad hardware are not loose or damaged, go to step  6.
    • Remove and inspect the worn disc brake pads for glazing, looseness, heat spots or damage.
    • Replace the worn disc brake pads as a complete axle set. See BRAKE PADS  under REMOVAL & INSTALLATION.
    If the inspection and replacement was completed, go to step  12.
    7. CAUTION: DO NOT disconnect the hydraulic brake flex hoses from the calipers.
    NOTE: Support the brake caliper with heavy mechanic's wire, or equivalent, whenever it is separated from its mount and the hydraulic flexible brake hose is still connected. Failure to support the caliper in this manner will cause the flexible brake hose to bear the weight of the caliper, which may cause damage to the brake hose and in turn may cause a brake fluid leak.
    1. Remove the front and/or rear disc brake calipers, as appropriate, from the mounting brackets and support the calipers. See BRAKE CALIPER  under REMOVAL & INSTALLATION.
    2. Inspect the disc brake caliper mounting bracket and the mounting/sliding hardware for the following conditions:
      • Binding or seized hardware.
      • Worn, damaged or missing hardware components.
      • Loose, bent, cracked, or damaged caliper mounting bracket.
      See DISC BRAKE MOUNTING & HARDWARE  under ADJUSTMENTS & INSPECTION.
    3. Replace components as required. Refer to the following procedures as required:
      • Replace the front and/or rear brake caliper bracket. See BRAKE CALIPER BRACKET  under REMOVAL & INSTALLATION.
      • Replace the front and/or rear disc brake hardware. See DISC BRAKE HARDWARE  under REMOVAL & INSTALLATION.
    4. Replace the unevenly-worn, loose or damaged disc brake pads as a complete axle set. See BRAKE PADS  under REMOVAL & INSTALLATION.
    If the inspection and replacement was completed, go to step  12.
    1. Inspect the disc brake calipers, brake hoses and brake pipes for evidence of an external brake fluid leak.
    2. Replace any components found to be leaking brake fluid. Refer to the following procedures as required:
      • Perform brake caliper overhaul. See BRAKE CALIPER  under OVERHAUL.
      • Replace appropriate brake hose. See BRAKE HOSE  under REMOVAL & INSTALLATION.
      • Replace brake pipe. See BRAKE PIPE  under REMOVAL & INSTALLATION.
      If the source of the leak causing contamination of the pads was found and corrected, go to step  11. If the source of the leak causing contamination of the pads was not found and corrected, go to step  9.
    1. Inspect the wheel drive shaft outer seals, if equipped, for damage and evidence of a grease leak.
    2. Replace any wheel drive shaft seal that is found to be leaking grease which may be the source of the contamination to the pads. See WHEEL DRIVE SHAFTS in DRIVELINE/AXLES.
    3. Inspect the rear axle seals for damage and evidence of a lubricant leak.
    4. Replace any rear axle seal that is found to be leaking lubricant which may be the source of the contamination to the pads. See WHEEL DRIVE SHAFTS in DRIVELINE/AXLES.
    If the source of the leak causing contamination of the pads was found and corrected, go to step  11. If the source of the leak causing contamination of the pads was not found and corrected, go to step  10.
    1. Inspect the automatic transmission cooling system lines, if equipped, for damage and evidence of an external fluid leak which may be the source of the contamination to the pads.
    2. Inspect the power steering system hoses for damage and evidence of an external fluid leak which may be the source of the contamination to the pads.
    3. Replace any components found to be leaking fluid which may be the source of the contamination to the pads.
    If the source of the leak causing contamination of the pads was found and corrected, go to step  11.
    11. CAUTION: DO NOT disconnect the hydraulic brake flex hoses from the calipers.
    NOTE: Support the brake caliper with heavy mechanic's wire, or equivalent, whenever it is separated from its mount and the hydraulic flexible brake hose is still connected. Failure to support the caliper in this manner will cause the flexible brake hose to bear the weight of the caliper, which may cause damage to the brake hose and in turn may cause a brake fluid leak.
    1. Clean the remaining disc brake system components to remove any traces of the contaminant.
    2. Remove the front and/or rear disc brake calipers, as appropriate, from the mounting brackets and support the calipers. See BRAKE CALIPER  under REMOVAL & INSTALLATION.
    3. Inspect the disc brake caliper mounting/sliding hardware for the following conditions: See DISC BRAKE MOUNTING & HARDWARE  under ADJUSTMENTS & INSPECTION.
      • Binding or seized hardware.
      • Distorted, worn, damaged or missing hardware components.
    4. Replace the caliper mounting/sliding hardware components as required. See DISC BRAKE HARDWARE  under REMOVAL & INSTALLATION.
    5. Replace the contaminated disc brake pads as a complete axle set. See BRAKE PADS  under REMOVAL & INSTALLATION.
    If the cleaning, inspection and replacement was completed, go to step  12.
  12. Visually inspect each of the disc brake rotor shields/backing plates for evidence of contact with the brake rotors. If any of the brake rotor shields/backing plates are contacting the brake rotors, go to step  13. If any of the brake rotor shields/backing plates are not contacting the brake rotors, go to step  14.
  13. Repair or replace the disc brake rotor shields/backing plates as required. See DISC BRAKE SPLASHSHIELD  under REMOVAL & INSTALLATION. If the repair or replacement was completed, go to step  14.
  14. Make the following determination individually for each rotor:
    1. Check the thickness of each of the disc brake rotors.
    2. Make a determination for each brake rotor if the rotor can be refinished and remain above the minimum requirements.
    See BRAKE ROTOR THICKNESS MEASUREMENT  under ADJUSTMENTS & INSPECTION. If the disc brake rotors meet the minimum requirements for refinishing, go to step  15. If the disc brake rotors DO NOT meet the minimum requirements for refinishing, go to step  18.
    15. NOTE: Make the following determination individually for each rotor.
  15. Inspect each of the disc brake rotors for thickness variation that exceeds the maximum acceptable level. See BRAKE ROTOR THICKNESS MEASUREMENT  under ADJUSTMENTS & INSPECTION. If the brake rotor exhibits thickness variation that exceeds the maximum acceptable level, go to step  17. If the brake rotor does not exhibit thickness variation that exceeds the maximum acceptable level, go to step  16.
  16. Make the following determination individually for each rotor:
    • Heavy rust and/or pitting.
    • Cracks and/or heat spots.
    • Excessive blueing discoloration.
    • Deep or excessive scoring 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 conditions listed previously, it requires refinishing. If the brake rotors require refinishing, go to step  17. If the brake rotors DO NOT require finishing, go to step  22.
  17. If you were able to refinish the brake rotor within the minimum requirements, go to step  22. If you were not able to refinish the brake rotor within the minimum requirements, go to step  21.
  18. If the brake rotor is at or below the discard requirements, go to step  21. If the brake rotor is not at or below the discard requirements, go to step  19.
    19. NOTE: Make the following determination individually for each rotor.
  19. Inspect each of the disc brake rotors for thickness variation that exceeds the maximum acceptable level. See BRAKE ROTOR THICKNESS MEASUREMENT  under ADJUSTMENTS & INSPECTION. If the brake rotor exhibits thickness variation that exceeds the maximum acceptable level, go to step  21. If the brake rotor does not exhibit thickness variation that exceeds the maximum acceptable level, go to step  20.
    1. 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.
      • Deep or excessive scoring beyond maximum acceptable level.
      See BRAKE ROTOR SURFACE & WEAR INSPECTION  under ADJUSTMENTS & INSPECTION.
    2. Make a determination for each brake rotor if the rotor requires replacement based upon the results of the inspection. If the brake rotor exhibits any of the conditions listed previously, it requires replacement. If the brake rotor requires replacement, go to step  21. If the brake rotor does not require replacement, go to step  22.
    21. NOTE: Whenever a brake rotor is replaced, the assembled Lateral Runout (LRO) of the rotor must be measured to ensure optimum performance of the disc brakes. See appropriate ANTI-LOCK article.
  21. Replace the brake rotor. See BRAKE ROTOR . After repairs are complete, go to step  24.
    22. NOTE: Make the following determination individually for each rotor.
  22. Inspect each of the disc brake rotors for assembled LRO that exceeds the maximum acceptable level. See appropriate ANTI-LOCK article. If the brake rotor exhibits assembled LRO that exceeds the maximum acceptable level, go to step  23. If the brake rotor does not exhibit assembled LRO that exceeds the maximum acceptable level, go to step  24.
  23. Correct the LRO for each brake rotor that was determined to have LRO exceeding the maximum acceptable level. See appropriate ANTI-LOCK article. If the operation was completed, go to step  24.
  24. Install or connect components that were removed or disconnected during diagnosis. If the operation was completed, disc brake system okay. If the operation was not completed, return to symptom list.
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