GM Service Manual Online
For 1990-2009 cars only

Master Cylinder

Warning: Refer to Brake Fluid Irritant Warning in the Preface section.

The master cylinder is designed for use in a diagonally split system. One front and one diagonally opposite rear brakes are served by the primary piston. The opposite front and rear brakes are served by the secondary piston. The master cylinder incorporates the functions of the standard dual master cylinder, plus a low fluid level indicator. The proportioning valve mounted to the bulkhead limits the outlet pressure to the rear brakes after a predetermined master cylinder pressure has been reached.

Note: Do not use lubricated shop air on the brake parts, because oil will damage the rubber components.

    • Replace all the components included in the repair kits used to service the master cylinder.
    • Lubricate the rubber parts with clean brake fluid to ease assembly.
    • If any hydraulic components is removed or disconnected, it may be necessary to bleed all or part of the brake system. Refer to Hydraulic Brake System Bleeding.
    • The torque values specified are for dry, unlubricated fasteners.
    • Perform all service operations on a clean bench, free from all traces of mineral oil.

Proportioning Valve

The proportioning valve limits the outlet pressure to the rear brakes after a predetermined master cylinder pressure has been reached. This is used when less rear application force is needed to obtain optimum braking.

Fluid Level Sensor

The master cylinder reservoir is equipped with a fluid level sensor. The sensor will activate the BRAKE lamp when the fluid level is low. The BRAKE lamp is also activated by the parking lever, and it turns on for a bulb test when the ignition is ON and the engine is not running. Refer to Diagnostic Starting Point - Hydraulic Brakes.