Primary and Secondary Pistons

Two closely fitted aluminum pistons are located in the master cylinder. The inner part of the piston is pressed against a rubber primary cup that prevents fluid from leaking past the piston. The outer end of the piston is pressed against a rubber secondary cup. This prevents the fluid from getting out of the master cylinder. The inner piston also has several little bleeder ports; there pass through the through the head to the base of the primary cup. Both of the piston assemblies are in the cylinder, and are kept there by a stop plate (or snap ring) in the end of the cylinder. A push rod, connected to the brake linkage, applies pressure to the pistons.