Chevrolet Citation/Omega/Phoenix/Skylark 1980-1985 Repair Guide

General Information


The X-Body cars have a diagonally-split hydraulic system. This differs from conventional practice in that the left front and right rear brakes are on one hydraulic circuit, and the right front and left rear are on the other.

A diagonally-split system necessitates the use of a special master cylinder design. The X-Body master cylinder incorporates the functions of a standard tandem master cylinder, plus a warning light switch and proportioning valves. Additionally, the master cylinder is designed with a quick take-up feature which provides a large volume of fluid to the brakes at low pressure when the brakes are initially applied. The low pressure fluid acts to quickly fill the large displacement requirements of the system.

The front disc brakes are single piston sliding caliper units. Fluid pressure acts equally against the piston and the bottom of the piston bore in the caliper. This forces the piston outward until the pad contacts the rotor. The force on the caliper bore forces the caliper to slide over, carrying the other pad into contact with the other side of the rotor. The disc brakes are self-adjusting.

Rear drum brakes are conventional duo-serve units. A dual piston wheel cylinder, mounted to the top of the backing plate, actuates both brake shoes. Wheel cylinder force to the shoes is supplemented by the tendency of the shoes to wrap into the drum (servo action). An actuating link, pivot and lever serve to automatically engage the adjuster as the brakers are applied when the car is moving in reverse. Provisions for manual adjustment are also provided. The rear brakes also serve as the parking brakes; linkage is mechanical.

Vacuum boost is an option. The booster is a conventional tandem vacuum unit.