Brake Master Cylinder

Brake Master Cylinder-Normal Conditions
The following conditions are considered normal and are not indications that the brake master cylinder is in need of repair or new installation.

Condition 1: During normal operation of the brake master cylinder, the brake fluid level in the brake master cylinder reservoir will fall during brake application and rise during release. The net brake fluid level will remain unchanged after brake application and release.

Condition 2: A trace of brake fluid may exist on the power brake booster shell below the brake master cylinder mounting flange. This is the result of the normal internal lubricating action of the brake master cylinder.

Condition 3: Brake fluid level will decrease as the brake shoes and linings wear.

Brake Master Cylinder-Abnormal Conditions
Changes in brake pedal feel and travel are indications that a brake system concern exists. Refer to the Symptom Chart for abnormal condition diagnosis. Symptom Related Diagnostic Procedures

Brake Master Cylinder-Bypass Condition Test
1. Check the brake hydraulic system for leaks or insufficient brake fluid. Repair as necessary.
2. Observe the brake fluid level in the brake master cylinder reservoir as the brake pedal is slowly pressed and quickly released. If the brake fluid level rises when the brake pedal is pressed and drops when the brake pedal is released, but the net brake fluid level remains unchanged, the brake master cylinder is bypassing. Repair or install a new brake master cylinder.

Brake Master Cylinder-Non-Pressure External Leaks
A low brake fluid level in the brake master cylinder reservoir may be caused by the following non-pressure external leaks:

Type 1: An external leak may exist at the brake master cylinder filler cap due to incorrect position of the cap, cap gasket, or cap gasket deterioration.

Type 2: An external leak may exist at the brake master cylinder mounting flange due to internal seal failure. Repair or install a new brake master cylinder.

Type 3: An external leak may exist at the base of the brake master cylinder reservoir due to deteriorated reservoir mounting seals. Repair or install a new brake master cylinder.

Brake Master Cylinder-Compensator Port Check
The purpose of the compensator ports in the brake master cylinder is to:
^ Supply additional brake fluid from the brake master cylinder reservoir needed by the brake system due to brake shoe and lining wear.
^ Allow brake fluid to return to the brake master cylinder reservoir when the brakes are released. The returning brake fluid will create a slight turbulence in the brake master cylinder reservoir. This is a normal condition and indicates that the compensator ports are not clogged.

Clogged compensator ports may cause the brakes to hang up or not fully release. If clogged compensator ports are suspected, proceed as follows:
1. Raise and support the vehicle.
2. With the brakes released, attempt to rotate each wheel. If an excessive amount of brake drag exists, continue with the test. If an excessive amount of brake drag exists at only one wheel, it indicates a possible seized rear disc brake caliper, front disc brake caliper, rear wheel cylinder, or parking brake component. Repair or install new components as necessary.
3. Check the Brake Pedal Position (BPP) switch adjustment, and brake pedal free play to verify that the brake pedal is not partially applied.
4. Loosen the nuts attaching the brake master cylinder to the power brake booster and pull the brake master cylinder away from the power brake booster.
5. Repeat Steps 1 and 2. If the brake drag disappears, the power brake booster is binding and new one must be installed. If the brake drag continues, the brake master cylinder is binding and new one must be installed.