Anyone who works on brakes should be familiar with basic hydraulics and the various components that make up the hydraulic portion of the brake system. So if you're not as familiar with this subject as you should be, keep reading and we'll refresh your memory.

We'll start at the heart of the system, which is the master cylinder. It converts the force exerted on the brake pedal by the vehicle's driver into hydraulic pressure to apply the brakes. Depressing the brake pedal moves a push rod in the master cylinder. Mounted on the push rod are a pair of pistons (primary and secondary) in tandem (one after the other) to push against the fluid in the master cylinder bore. This creates pressure that displaces fluid since it's incompressible. As fluid is pushed from the master cylinder, it exerts pressure through the brake lines to apply each of the brakes.

When the brake pedal is released, the spring-loaded piston assembly in the master cylinder returns to its rest position. The fluid that was displaced by the pistons is pushed back to the master cylinder as the disc brake pads kick out away from the rotors, and the springs inside the drums retract the brake shoes. The fluid returns to the fluid reservoir through the "compensating ports," which are small openings between the master cylinder bore and fluid reservoir just ahead of each of the pistons.

Master cylinders are divided into two separate hydraulic circuits, with ea...