Brake Master Cylinder - Compensator Port

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:

1. With the vehicle in NEUTRAL, position it on a hoist. For additional information, refer to JACKING AND LIFTING article.
2. 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 1 wheel, it indicates a possible seized brake caliper, brake wheel cylinder or parking brake component. Repair or install new components as necessary.
3. Check the brake stoplamp switch, speed control deactivator switch and the brake pedal free play to verify that the brake pedal is not partially applied.
NOTE: If the booster vacuum is not depleted, the seal between the booster and the master cylinder can be drawn into the booster when the 2 components are separated.
4. Press the brake pedal several times to deplete the vacuum in the booster.
5. Loosen the brake master cylinder nuts and position the brake master cylinder away from the brake booster.
6. 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.