553 Brake Systems Technician Handbook Brake Application When the brakes are applied: • The brake pushrod moves the primary piston to the left. • The piston cup passes the compensating port, sealing the primary chamber. As the piston continues to move to the left pressure builds in the primary chamber and is transmitted to: • Two wheel cylinders • The secondary piston The secondary piston moves to the left, transmitting pressure to the other two wheel cylinders. 12 Technical Training