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Hydraulic Brake System Diagnosis

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
  1. If you were sent here from a brake symptom list, go to step  2 . If you were not sent here from a brake symptom list, see DIAGNOSTIC STARTING POINT (HYDRAULIC BRAKES)  under TROUBLE SHOOTING.
  2. Inspect and adjust the brake fluid level in the brake master cylinder. If the brake fluid level is low, go to step  3 . If the brake fluid level was not low, go to step  4 .
  3. Inspect the brake fluid for the following conditions, indicating brake fluid contamination:
    • Fluid separation, indicating 2 types of fluid are present:
      1. Swirled appearance - oil-based substance.
      2. Layered appearance - silicone-based substance.
    • Fluid discoloration:
      1. Cloudy appearance - moisture.
      2. Dark appearance/suspended particles in fluid - dirt, rust, corrosion, brake dust.
    Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for swelling, indicating fluid contamination. If any of the above conditions exist, go to step  5 . If none of the above conditions exist, go to step  6 .
    • Fluid separation, indicating 2 types of fluid are present:
      1. Swirled appearance - oil-based substance.
      2. Layered appearance - silicone-based substance.
    • Fluid discoloration:
      1. Cloudy appearance - moisture.
      2. Dark appearance/suspended particles in fluid - dirt, rust, corrosion, brake dust.
    Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for swelling, indicating fluid contamination. If any of the above conditions exist, go to step  5 . If none of the above conditions exist, go to step  12 .
  5. Flush the hydraulic brake system. If the brake fluid WAS contaminated with an oil-based or a silicone-based fluid, indicated by fluid separation and/or a swollen master cylinder reservoir cap diaphragm and/or swollen reservoir-to-master cylinder grommets, perform the following steps. Refer to the procedures indicated.
    1. Remove all of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
    2. Dry the brake pipes using non-lubricated, filtered air.
    3. Repair or replace ALL of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
      • Master Cylinder: Perform master cylinder overhaul if necessary, see MASTER CYLINDER  under OVERHAUL, and/or replace master cylinder if necessary. See MASTER CYLINDER  under REMOVAL & INSTALLATION.
      • Brake master cylinder reservoir: Clean the brake master cylinder reservoir using denatured alcohol, or equivalent, then dry the reservoir using non-lubricated, filtered air, or if necessary, replace the brake master cylinder reservoir.
      • Replace the brake master cylinder reservoir cap diaphragm.
      • Replace the front brake hose. See FRONT BRAKE HOSE  under REMOVAL & INSTALLATION.
      • Replace rear brake hose. See REAR BRAKE HOSE  under REMOVAL & INSTALLATION.
      • Perform front brake caliper overhaul if necessary. See FRONT CALIPERS  under OVERHAUL. Replace front brake calipers if necessary. See FRONT BRAKE CALIPER  under REMOVAL & INSTALLATION.
      • Perform rear brake caliper overhaul if necessary. See REAR CALIPERS  under OVERHAUL. Replace rear brake calipers if necessary. See REAR BRAKE CALIPER  under REMOVAL & INSTALLATION.
      • Replace Brake Pressure Modulator Valve (BPMV). See appropriate ANTI-LOCK BRAKE article.
    4. If the brake fluid was NOT contaminated with an oil-based fluid, but was contaminated with water or dirt, rust, corrosion, and/or brake dust, replace the brake master cylinder reservoir cap diaphragm which may have allowed moisture or dirt to enter the system.
    5. Refill and bleed the hydraulic brake system. See BLEEDING BRAKE SYSTEM  . If the operation and any required repairs and/or replacements have been completed, go to step  9 .
  6. Inspect the following hydraulic brake system components for external fluid leaks. Repair or replace any of the components found to be leaking brake fluid. Refer to the appropriate procedures:
    • Perform master cylinder overhaul if necessary, see MASTER CYLINDER  under OVERHAUL, and/or replace master cylinder if necessary. See MASTER CYLINDER  under REMOVAL & INSTALLATION.
    • Brake master cylinder reservoir: Clean the brake master cylinder reservoir using denatured alcohol, or equivalent, then dry the reservoir using non-lubricated, filtered air, or if necessary, replace the brake master cylinder reservoir.
    • Replace the brake master cylinder reservoir cap diaphragm.
    • Replace the front brake hose. See FRONT BRAKE HOSE  under REMOVAL & INSTALLATION.
    • Replace rear brake hose. See REAR BRAKE HOSE  under REMOVAL & INSTALLATION.
    • Perform front brake caliper overhaul if necessary. See FRONT CALIPERS  under OVERHAUL. Replace front brake calipers if necessary. See FRONT BRAKE CALIPER  under REMOVAL & INSTALLATION.
    • Perform rear brake caliper overhaul if necessary. See REAR CALIPERS  under OVERHAUL. Replace rear brake calipers if necessary. See REAR BRAKE CALIPER  under REMOVAL & INSTALLATION.
    • Replace Brake Pressure Modulator Valve (BPMV). See appropriate ANTI-LOCK BRAKE article.
    If you repaired or replaced any of the brake system components listed, bleed the hydraulic brake system. See BLEEDING BRAKE SYSTEM  . While bleeding the hydraulic brake system, observe for the following conditions:
    • The presence of air in the system at a bleeder valve location other than at the repair location, except if the brake master cylinder was replaced.
    • An unrestricted and even flow of brake fluid per axle during the bleeding procedure.
    If the condition was found and corrected, go to step  7 . If the condition was not found and corrected, go to step  12 .
  7. If there was air in the system at a bleeder valve location other than at the repair location, except if the brake master cylinder was replaced, go to step  19 . If there was no air in the system, go to step  8 .
  8. If the flow of brake fluid was unrestricted and even per axle during the bleeding procedure, go to step  9 . If the flow was not unrestricted and even during the bleeding procedure, go to step  10 .
  9. Inspect the hydraulic function of the brake calipers for proper operation. See HYDRAULIC BRAKE COMPONENT OPERATION INSPECTION  under ADJUSTMENTS & INSPECTION. If the hydraulic function of the brake calipers were operating properly, go to step  21 . If the hydraulic function of the brake calipers were not operating properly, go to step  14 .
  10. If the flow of brake fluid was restricted or uneven through front axle hydraulic components during the bleeding procedure, go to step  13 . If the flow was not unrestricted and even during the bleeding procedure, go to step  11 .
  11. If the flow of the brake fluid was restricted or uneven through rear axle hydraulic components during the bleeding procedure, go to step  17 .
  12. Inspect the hydraulic function of the brake calipers for proper operation. See HYDRAULIC BRAKE COMPONENT OPERATION INSPECTION  under ADJUSTMENTS & INSPECTION. If the hydraulic function of the brake calipers were operating properly, go to step  15 . If the hydraulic function of the brake calipers were not operating properly, go to step  13 .
  13. Determine if the brake caliper is restricting the flow of brake fluid and/or not operating properly:
    1. Raise and support the vehicle.
    2. Remove the tire and wheel assemblies.
    3. Open the suspected caliper bleeder valve.
    4. Using a large C-clamp, compress the caliper piston and observe for an unrestricted flow of brake fluid and for free movement of the caliper piston.
    5. Close the caliper bleeder valve.
    If the flow of the brake fluid was unrestricted and the caliper piston moved freely, go to step  17 . If the flow of the brake fluid was not unrestricted and the caliper piston did not move freely, go to step  14 .
  14. Perform front brake caliper overhaul if necessary. See FRONT CALIPERS  under OVERHAUL. Replace front brake calipers if necessary. See FRONT BRAKE CALIPER  under REMOVAL & INSTALLATION. Perform rear brake caliper overhaul if necessary. See REAR CALIPERS  under OVERHAUL. Replace rear brake calipers if necessary. See REAR BRAKE CALIPER  under REMOVAL & INSTALLATION. If the repair and/or replacement has been completed, go to step  21 .
  15. Bleed the hydraulic brake system to observe for the presence of air in the system and to observe for an unrestricted and even flow of brake fluid per axle during the bleeding procedure. See BLEEDING BRAKE SYSTEM  . If there was air in the system, go to step  19 . If there was no air in the system, go to step  16 .
  16. If the flow of brake fluid was unrestricted and even per axle during the bleeding procedure, go to step  21 . If the flow of brake fluid was not unrestricted and even per axle, go to step  17 .
    1. Inspect the hydraulic brake pipes and flexible brake hoses for signs of a fluid restriction; such as being bent, kinked, pinched or damaged.
    2. Replace any of the hydraulic brake pipes and/or flexible brake hoses found to be bent, kinked, pinched, or damaged. Refer to the following procedures as necessary:
      • Replace front brake hose. See FRONT BRAKE HOSE  under REMOVAL & INSTALLATION.
      • Replace rear brake hose. See REAR BRAKE HOSE  under REMOVAL & INSTALLATION.
      • Replace the brake pipe. See BRAKE PIPE  under REMOVAL & INSTALLATION.
    3. If none of the hydraulic brake pipes or flexible brake hoses were visibly bent, kinked, pinched, or damaged, replace the hydraulic brake flex hose at the restricted location.
    If the condition was found and corrected, go to step  21 . If the condition was not found and corrected, go to step  18 .
  18. Replace the brake pressure modulator valve, in order to correct the hydraulic brake dynamic rear proportioning mechanical operation. See appropriate ANTI-LOCK BRAKE article. If the replacement was completed, go to step  21 .
    1. Inspect the hydraulic brake system components for brake fluid seepage at a seal and/or fitting location, which may have drawn air into the system.
    2. Inspect the hydraulic brake system components for evidence of a recent repair, which may have introduced air into the system.
    3. Repair or replace any of the components found to be installed incorrectly or seeping brake fluid.
    If the condition was found and corrected, go to step  21 . If the condition was not found and corrected, go to step  20 .
    1. Inspect the brake master cylinder for internal fluid leaks. See BRAKE SYSTEM INTERNAL LEAK TEST  .
    2. Repair or replace the brake master cylinder if it is found to be leaking brake fluid internally. Perform master cylinder overhaul if necessary, see MASTER CYLINDER  under OVERHAUL, and/or replace master cylinder if necessary. See MASTER CYLINDER  under REMOVAL & INSTALLATION.
    If the condition was found and corrected, go to step  21 . If the condition was not found and corrected, see SYMPTOMS (HYDRAULIC BRAKES)  under TROUBLE SHOOTING.
  21. Install or connect components that were removed or disconnected during diagnosis. If the operation was completed, hydraulic brake system is okay. If the operation was not completed, see SYMPTOMS (HYDRAULIC BRAKES)  under TROUBLE SHOOTING.
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