GM Service Manual Online
For 1990-2009 cars only

Dual Piston Caliper


Object Number: 370899  Size: MF

The front brake caliper has a dual piston. Two mounting bolts hold the caliper in place. The caliper is mounted on the steering knuckle. The caliper moves laterally on the steering knuckle when the brakes are applied. The caliper is a one-piece casting with the piston bore(s) in the inboard side. A square-cut rubber seal fits in a groove in each piston bore. The square-cut rubber seal provides a hydraulic seal between the piston and the caliper bore.

The front disc brakes use a combination rotor and hub assembly. The rotor is separate from the hub.

The rotor turns freely between the linings, until the caliper forces the linings against the rotor. The vented area between the rotor braking surfaces allows for efficient heat dissipation.

Rear Disc Caliper


Object Number: 370900  Size: MF

The rear brake caliper housing has a single bore. The caliper mounts to the anchor bracket with two guide pin bolts. Fluid pressure behind the caliper piston increases when applying the brakes. Pressure exerts equally against the bottom of the piston and the bottom of the piston bores. The pressure that applies to the piston transmits to the inner pad. The pressure forces the pad against the inner rotor surface. The pressure that applies to the bottom of the piston bores forces the caliper to slide on the mounting bolts. The caliper slides to the center of the vehicle. Because the caliper is one piece, the sliding movement causes the outer section of the caliper to apply pressure against the back of the outer pad. The pressure then forces the pad against the outer rotor surface. As line pressure builds, the pads press against the rotor surfaces with increased force. The force brings the vehicle to a stop. When releasing the brake pedal, the line pressure releases. The seal and the seal groove cause the piston to retract slightly. Piston retraction causes less drag on the rotor by both pads. Outward movement of the piston and inward movement of the caliper automatically compensate for pad wear. As the pads wear, the increased area behind the piston fills with brake fluid from the master cylinder reservoir.

The park brake is completely independent of the hydraulic braking system. For more information on the park brake, refer to System Description in Park Brake.

Servicing Information

    • Replace all components included in the repair kits.
    • Lubricate the parts as specified.
    • Do not use lubricated shop air on the brake parts. Shop air can damage the rubber components.
    • If necessary, bleed all or part of the brake system after any hydraulic component has been removed or disconnected.
    • Replace brake pads in axle sets only.
    • The torques specified are for dry, unlubricated fasteners.
    • Perform service operations on a clean bench. Verify that the bench is free from mineral oil and other contaminants.
    • Use extreme care when doing any work around antilock components in order to prevent damage or misalignment.
    • Pump the brake pedal several times in order to make sure it is firm prior to moving the vehicle. Do not move the vehicle until a firm pedal has been obtained. Check the brake fluid level in the master cylinder after pumping the brakes.