The Chevrolet drum brake wheel cylinder is the equivalent of the caliper in a disc brake system. This is the hydraulic part which applies the pressure to the brake shoes and makes it possible for your Chevrolet to stop. The drum brake wheel cylinder is located on the upper portion of the backing plate of your drum brakes. It pushes out against the brake shoes which place force against the drums stopping your Chevrolet. These wear out over time as the seals in the drum brake wheel cylinder develop cracks and splits causing hydraulic fluid to leak. A driver will not be able to see this unless they tear apart the rear brakes and look directly at them. The best way to know there is a problem is to observe a small puddle of brake fluid at the center of the rear wheel on the inside. This is an indication that hydraulic fluid is leaking and the seals on your Chevrolet drum brake wheel cylinders are the only possible place for the formation of this puddle on the surface of the pavement. The rebuilding of the drum brake wheel cylinder was very common in the past during a routine brake job. Today to increase the speed of the repair job and the better availability of rebuilt parts, it is no longer done at the time of the repair. They are now sent out to another shop to have the seals replaced. The danger of a drum brake wheel cylinder leaking on your Chevrolet is that it places the hydraulic fluid directly on the drums of the brakes. This reduces the braking potential of the rear brakes. Since it is a hydraulic leak, total brake failure can also occur.