Disc Brake System: Description and Operation

DISC BRAKES SYSTEM DESCRIPTION
The disc brake assembly consists of a caliper assembly, rotor, linings, anchor plate, and pads mounted to the steering knuckle. The caliper mounts in a way that allows it to move laterally against the rotor. The caliper is a one-piece casting with the inboard side containing the piston bore. A square cut rubber sea] fits in a groove in the piston bore to provide a hydraulic seal and return mechanism for the piston.

Applying the brake pedal causes the hydraulic pressure that moves the caliper piston. The piston then forces the inboard brake lining assembly against the inboard braking surface of the rotor. Increasing the force against the rotor causes the caliper to move inboard. The outer brake lining assembly then contacts the outboard braking surface of the rotor. The force of the two lining assemblies provides the desired clamping action on the rotor.

Releasing the brake pedal relieves the pressure applied on the piston. The square cut seal on the piston relaxes and the seal allows a running clearance between the brake lining assemblies and the rotor.


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, shoes and linings 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.


ROTOR
The front disc brakes use one of four different styles of rotors. The smaller two wheel drive models (C1, C2, and C3) use standard 1.250 inch rotors. The heavy duty two wheel drive model (C3500 HD) has four wheel disc brakes with 1.435 inch rotors. The smaller four wheel drive models (K1 and K2) use a composite rotor. The larger four wheel drive models (K2 and K3) use 1.250 inch rotors on single wheel models and 1.5 inch rotors on dual wheel models. The 1.250 inch rotors are three-piece assemblies consisting of a rotor, the bearings, and a hub. Models with dual rear wheels (RO5) use a four-piece rotor assembly consisting of a rotor, the bearings, a hub, and an extension.

The rear disc brakes use a combination rotor and hub assembly. The rotor is integral with the rear hub. During operation, the rotor turns between the linings and the basically free-wheels until the linings begin to apply a clamping action onto the rotor. the vented area between the rotor braking surfaces allows for efficient heat dissipation


CALIPER
The front disc brakes use three different types of calipers. The Delco 3400 calipers with 75 and 80 mm single bores are used on the models with a 9600 or lower GVW rating. The Delco 3486 calipers with an 86 mm single bore is used on models with 10,000, 11,000, and 12,000 GVW ratings. The C350OHD model uses a Bendix single bore caliper.

The rear disc brakes use a Bendix caliper.

The Delco calipers mount to the support bracket using two bolts. The Bendix caliper mounts to the support bracket using a support key, a spring, and a bolt assembly.