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Hydraulic Brake System Testing

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
  1. Were you sent here from a Brake Symptom table? If so, go to next step. If not, see DIAGNOSTIC STARTING POINT - HYDRAULIC BRAKE  under TROUBLE SHOOTING.
  2. Inspect and adjust the brake fluid level in the brake master cylinder. See MASTER CYLINDER RESERVOIR FILLING  under BLEEDING, FILLING & FLUSHING BRAKE SYSTEM. Was the brake fluid level low? If so, go to next step. If not, go to step  3 .
  3. Inspect the brake fluid for the following conditions, indicating brake fluid contamination:

    Fluid Separation, Indicating Two Types Of Fluid Are Present

    • Swirled appearance, oil-based substance.
    • Layered appearance, silicone-based substance.

    Fluid Discoloration

    • Cloudy appearance, moisture.
    • 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. Do any of the above conditions exist? If so, go to next step. If not, go to step  11 .
  4. Flush the hydraulic brake system. See HYDRAULIC BRAKE SYSTEM FLUSHING  under BLEEDING, FILLING & FLUSHING 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.
    • Remove ALL of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
    • Clean out the hydraulic brake pipes using denatured alcohol, or equivalent.
    • Dry the brake pipes using non-lubricated, filtered air.
    • Repair or replace ALL of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
      1. MASTER CYLINDER  under OVERHAUL or MASTER CYLINDER  under REMOVAL & INSTALLATION.
      2. 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.
      3. Replace the brake master cylinder reservoir cap diaphragm.
      4. FRONT BRAKE HOSE  under REMOVAL & INSTALLATION.
      5. REAR BRAKE HOSE  under REMOVAL & INSTALLATION.
      6. FRONT BRAKE CALIPER  or FRONT BRAKE CALIPER  under REMOVAL & INSTALLATION.
      7. REAR BRAKE CALIPER  or REAR BRAKE CALIPER  under REMOVAL & INSTALLATION
      8. See BRAKE PRESSURE MODULATOR VALVE (BPMV) in appropriate ANTI-LOCK BRAKE SYSTEM article.
    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. Refill and bleed the hydraulic brake system. See MANUAL BLEEDING  under BLEEDING, FILLING & FLUSHING BRAKE SYSTEM. Did you complete the operation and any required repairs and/or replacements? If so, go to step  8 .
  5. Inspect the following hydraulic brake system components for external fluid leaks. Repair or replace any of the following components found to be leaking brake fluid: If you repaired or replaced any of the brake system components listed, bleed the hydraulic brake system. See MANUAL BLEEDING  under BLEEDING, FILLING & FLUSHING 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.
    Did you find and correct a condition? If so, go to next step. If not, go to step  11 .
  6. Was there air in the system at a bleeder valve location other than at the repair location, except if the brake master cylinder was replaced? If so, go to step  18 . If not, go to next step.
  7. Was the flow of brake fluid unrestricted and even per axle during the bleeding procedure? If so, go to next step, if no, go to step  9 .
  8. Inspect the hydraulic function of the brake calipers for proper operation. See HYDRAULIC BRAKE COMPONENT OPERATION VISUAL INSPECTIONS  under ADJUSTMENTS & INSPECTIONS. Was the hydraulic function of the brake calipers operating properly? If so, go to step  20 . If not, go to step  13 .
  9. Was the flow of brake fluid restricted or uneven through front axle hydraulic components during the bleeding procedure? If so, go to step  12 . If not, go to next step.
  10. Was the flow of brake fluid restricted or uneven through rear axle hydraulic components during the bleeding procedure? If so, go to step  16 .
  11. Inspect the hydraulic function of the brake calipers for proper operation. See HYDRAULIC BRAKE COMPONENT OPERATION VISUAL INSPECTION  under ADJUSTMENTS & INSPECTIONS. Was the hydraulic function of the brake calipers operating properly? If so, go to step  14 . If not, go to next step.
  12. Determine if the brake caliper is restricting the flow of brake fluid and/or not operating properly:
    • Raise and support the vehicle.
    • Remove the tire and wheel assemblies.
    • Open the suspected caliper bleeder valve.
    • 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.
    • Close the caliper bleeder valve.
    Was the flow of brake fluid unrestricted and did the caliper piston move freely? If so, go to  16 . If not, go to next step.
  13. Repair or replace any brake caliper that was not operating properly. Refer to the appropriate procedure: After repairs are complete, go to step  20 .
  14. 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 MANUAL BLEEDING  under BLEEDING, FILLING & FLUSHING BRAKE SYSTEM. Was there air in the system? If so, go to step  18 . If not, go to next step.
  15. Was the flow of brake fluid unrestricted and even per axle during the bleeding procedure? If so, go to step  20 . If not, go to next step.
  16. Inspect the hydraulic brake pipes and flexible brake hoses for signs of a fluid restriction; such as being bent, kinked, pinched or damaged. See BRAKE PIPE & HOSE  under ADJUSTMENTS & INSPECTIONS. 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: 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. Did you find and correct a condition? If so, go to step  20 . If not, go to next step.
  17. Replace the brake pressure modulator valve (BPMV), in order to correct the hydraulic brake dynamic rear proportioning mechanical operation. See appropriate BRAKE PRESSURE MODULATOR VALVE (BPMV) REPLACEMENT in ANTI-LOCK BRAKE SYSTEM article. After repairs are complete, go to step  20 .
  18. 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. Inspect the hydraulic brake system components for evidence of a recent repair, which may have introduced air into the system. Repair or replace any of the components found to be installed incorrectly or seeping brake fluid. Did you find and correct a condition? If so, go to step  20 . If not, go to next step.
  19. Inspect the brake master cylinder for internal fluid leaks. See BRAKE SYSTEM INTERNAL LEAK TEST  under SYMPTOM TESTING. Repair or replace the brake master cylinder if it is found to be leaking brake fluid internally. See MASTER CYLINDER  or MASTER CYLINDER  under REMOVAL & INSTALLATION. Did you find and correct a condition? If so, go to next step.
  20. Install or connect components that were removed or disconnected during diagnosis. Did you complete the operation? If so, then system is okay.
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