Hydraulic Brake System Diagnosis

1. Inspect the brake fluid for fluid separation, indicating 2 types of fluid are present and brake fluid is contaminated:
   • Swirled appearance - oil-based substance.
   • Layered appearance - silicone-based substance.
2. Inspect the brake fluid for fluid discoloration, indicating 2 types of fluid are present and brake fluid is contaminated:
   • Cloudy appearance - moisture.
   • Dark appearance/suspended particles in fluid - dirt, rust, corrosion, brake dust.
3. Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for swelling, indicating fluid contamination.

1. Inspect the brake fluid for fluid separation, indicating 2 types of fluid are present and brake fluid is contaminated:
   • Swirled appearance - oil-based substance.
   • Layered appearance - silicone-based substance.
2. Inspect the brake fluid for fluid discoloration, indicating 2 types of fluid are present and brake fluid is contaminated:
   • Cloudy appearance - moisture.
   • Dark appearance/suspended particles in fluid - dirt, rust, corrosion, brake dust.
3. 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  12.

1. Flush the hydraulic brake system.
2. 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:
   1. Remove all of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
   2. Clean out the hydraulic brake pipes using denatured alcohol, or equivalent.
   3. Dry the brake pipes using non-lubricated, filtered air.
   4. Repair or replace all of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
      • Master Cylinder  - Overhaul or replace master cylinder. For master cylinder overhaul, see OVERHAUL . For master cylinder replacement, see MASTER CYLINDER  under REMOVAL & INSTALLATION.
      • Brake Master Cylinder Reservoir  - Clean the brake master cylinder reservoir using denatured alcohol, or equivalent. Dry the master cylinder reservoir using non-lubricated, filtered air. If necessary, replace the brake master cylinder reservoir.
      • Brake Master Cylinder Reservoir Cap Diaphragm  - Replace the brake master cylinder reservoir cap diaphragm.
      • Brake Hoses  - For brake hose replacement, see BRAKE HOSE  under REMOVAL & INSTALLATION.
      • Brake Calipers  - For brake caliper overhaul, see OVERHAUL . For brake caliper replacement, see FRONT BRAKE CALIPER  or REAR BRAKE CALIPER  under REMOVAL & INSTALLATION.
      • Brake Pressure Modulator Valve  - See appropriate ANTI-LOCK article.
3. 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.
4. Refill and bleed the hydraulic brake system. See BLEEDING BRAKE SYSTEM .

1. Inspect the following hydraulic brake system components for external fluid leaks. Repair or replace any of the components found to be leaking brake fluid.
   • Master Cylinder  - Overhaul or replace master cylinder. For master cylinder overhaul, see OVERHAUL . For master cylinder replacement, see MASTER CYLINDER  under REMOVAL & INSTALLATION.
   • Brake Hoses  - For brake hose replacement, see BRAKE HOSE  under REMOVAL & INSTALLATION.
   • Brake Calipers  - For brake caliper overhaul, see OVERHAUL . For brake caliper replacement, see FRONT BRAKE CALIPER  or REAR BRAKE CALIPER  under REMOVAL & INSTALLATION.
   • Brake Pressure Modulator Valve  - See appropriate ANTI-LOCK article.
2. 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.

   Did you find and correct a condition? If so, go to next step. If not, go to step  12.

• 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.

• Inspect the hydraulic brake pipes and flexible brake hoses for signs of a fluid restriction; such as being bent, kinked, pinched or damaged.
• Replace any of the hydraulic brake pipes and/or flexible brake hoses found to be bent, kinked, pinched, or damaged.
• 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.

• 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.