Brake Master Cylinder - Compensator Port

WARNING: This page is about a different car, the 2009 Mercury Grand Marquis and 2009 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

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 lining wear.
allow brake fluid to return to the brake master cylinder reservoir when the brakes are released. The returning brake fluid creates 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:

WARNING: Before servicing a vehicle equipped with a fire suppression system, depower the system by following the procedure in FIRE SUPPRESSION SYSTEM article. Failure to follow the instructions may result in serious personal injury.

If equipped with a fire suppression system, depower the system. Refer to FIRE SUPPRESSION SYSTEM article.
With the vehicle in NEUTRAL, position it on a hoist. Refer to JACKING & LIFTING article.
With the brakes released, attempt to rotate each wheel and check for any brake drag.
- If an excessive amount of brake drag exists at all 4 wheels, continue with the test.
- If an excessive amount of brake drag exists at only one wheel, it indicates a possible seized brake caliper, brake wheel cylinder or parking brake component. Repair or install new components as necessary.
Check the brake stoplamp switch and the brake pedal free play to verify that the brake pedal is not partially applied.
Loosen the brake master cylinder nuts and position the brake master cylinder away from the brake booster.
With the brakes released, attempt to rotate each wheel and check for any brake drag.
- If the brake drag is no longer present, install a new brake booster. Refer to POWER BRAKE ACTUATION article.
- If the brake drag is still present, install a new master cylinder. Refer to HYDRAULIC BRAKE ACTUATION article.

WARNING: If the vehicle is equipped with a fire suppression system, repower the system. For important safety warnings and procedures, refer to FIRE SUPPRESSION SYSTEM article. Failure to follow these instructions may result in serious personal injury.

If equipped with a fire suppression system, repower the system. Refer to FIRE SUPPRESSION SYSTEM article.