This rear brake disc is the friction element in the service brake assembly for the host tractor. It sits between the pressure plate and the hub flange on the axle shaft; when the brake pedal is applied, hydraulic or mechanical force clamps the disc between the stationary and rotating surfaces to slow the wheel. Wear on the disc friction faces reduces clamping force and increases pedal travel, eventually leading to insufficient braking torque. The disc is manufactured to the original thickness and surface finish, which maintains the correct clearance in the caliper or dry-brake housing. On reinstallation, inspect the mating surfaces for scoring and replace any worn seals in the actuator.