553 Brake Systems Technician Handbook Master Cylinder Components The master cylinder body houses the following components: • Compensating port: A narrow passage between the fluid reservoir and the brake cylinder that equalizes pressure between the reservoir and cylinder chamber when the brakes are released. • Inlet port: An unrestricted passage that prevents air from being drawn into the system as the brake is released. • Piston cups: Seals that block the flow of fluid between chambers. • Return springs: Heavy springs that keep the moving components in place when the brakes are not applied. • Stopper bolt: A stopper that limits secondary piston travel.
When the system is at rest and the brakes are not applied: • The piston cups attached to the face of the primary and secondary pistons are positioned between compensating port and inlet port. • Fluid moves freely between the reservoir and cylinder via the compensating port. Technical Training 11