GM Service Manual Online
For 1990-2009 cars only

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

Notice: Do not use lubricated compressed air on brake parts as damage to rubber components may result.

The master cylinder is designed for use in a diagonal split system. One front and one diagonally opposite rear brake 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 and the proportioning valves in the non-antilock braking system. The proportioning valves limit the outlet pressure to the rear brakes after a predetermined master cylinder pressure has been reached.

    •  Replace all the components included in the repair kits used to service this master cylinder.
    •  Lubricate rubber parts with clean brake fluid to ease assembly.
    • If any hydraulic component is removed or disconnected, it may be necessary to bleed all or part of the brake system.
    • 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 Valves

The proportioning valves limit the outlet pressure to the rear brakes on the non-antilock braking system after a predetermined master cylinder pressure has been reached. This is used when less rear apply force is needed to obtain optimum braking and is usually found on disc/drum brake configurations. On ABS-equipped vehicles, refer to ABS Component Specifications .

Fluid Level Sensor

The master cylinder is equipped with a fluid level sensor. This sensor will activate the BRAKE light if a low fluid level condition is detected. Once the fluid level is corrected, the BRAKE light will go out.