Initial Inspection and Diagnostic Overview

NORMAL CONDITIONS - Usually the first and strongest indicator of anything wrong in the brake system is a feeling through the brake pedal. The following conditions are considered normal and are not indications the brake master cylinder is in need of service:

^ New brake systems are not designed to produce as hard a pedal effort as in the past. Complaints of light pedal efforts should be compared to pedal efforts on another vehicle, same model and year.
^ A momentary or slight squirt of brake fluid from the brake master cylinder reservoir upon application of the brake pedal; this condition is caused by fluid displacement through the brake master cylinder reservoir compensating port as the brake master cylinder pistons move forward in the bore when the brakes are applied.
^ A slight turbulence in the brake master cylinder reservoir fluid occurring when the brake pedal is released. Turbulence occurs as brake fluid returns to the brake master cylinder after releasing the brakes.
^ A trace of brake fluid exists on booster shell below the brake master cylinder mounting flange. This condition results from the lubricating action of the master cylinder wiping seal.
^ Low fluid level detected without signs of leakage; this condition is caused by displacement of fluid from the brake master cylinder reservoir into the disc brake calipers to compensate for normal brake wear. Add the specified fluid as needed.
^ During normal operation of the brake master cylinder, the fluid level in the brake master cylinder reservoir will rise during brake application and fall during release. The net fluid level, after brake application and release, will remain unchanged.
^ When a low brake pedal or the feel of a bottomed-out condition exists, check for brake pedal reserve. Refer to Procedures. Component Tests

ABNORMAL CONDITIONS - The diagnosic procedures and techniques use brake pedal feel, warning indicator illumination, and brake fluid level as indicators in diagnosing brake system concerns. The following conditions are considered abnormal and indicate that the brake master cylinder is in need of service.


NOTE: Prior to performing any diagnosis, make sure the brake system warning indicator is functional.

^ Brake pedal goes down fast. This could be caused by an external or internal leak.
^ Brake pedal eases down slowly. This could be caused by an external or internal leak.
^ Brake pedal is low or feels spongy. This condition may be caused by no fluid in the brake master cylinder reservoir, reservoir cap vent holes clogged, rear brakes out of adjustment or air in the hydraulic system.
^ Brake pedal effort is excessive. This may be caused by a bind or obstruction in brake pedal linkage or insufficient power brake booster vacuum.
^ Rear brakes lock up during light brake pedal force. This may be caused by wrong tire pressure grease or fluid on linings, damaged linings, improperly adjusted parking brakes or damaged/contaminated brake pressure control valve.
^ Brake pedal effort is erratic. This condition could be caused by power brake booster malfunction extreme caliper piston knock back or improperly installed disc brake shoe and lining.
^ Brake warning indicator is "ON". This may be caused by low fluid level, ignition wire routing too close to fluid level indicator assembly or float assembly damage. A binding parking brake system will also cause the Brake warning indicator to remain "ON".