553 Brake Systems Technician Handbook Brake Release When the brakes are released: • The primary and secondary return springs return both pistons to their at rest positions. • The stopper bolt keeps the secondary piston from moving too far to the right. The pistons return to their original positions more quickly than the fluid returns from the system, so: • System pressure briefly drops below normal • Fluid from the inlet port flows through small orifices in the pistons and past the piston cup, preventing air from entering the system. Technical Training 13