Master cylinder assembly (Brakes) (page 2 of 2)

Brakes applied When the brake pedal is pressed, the output rod in the brake servo assembly pushes the primary piston along the cylinder bore. This produces pressure in the primary pressure chamber which, in conjunction with the primary spring, overcomes the secondary spring and simultaneously moves the secondary piston along the cylinder bore. The initial movement of the pistons, away from the piston stops, closes the primary and secondary centre valves. Further movement of the pistons then pressurizes the fluid in the primary and secondary pressure chambers, and thus the brake circuits. The fluid in the chambers behind the pistons is unaffected by movement of the pistons and can flow unrestricted through the feed holes between the chambers and the reservoir.

Brakes released When the brake pedal is released, the primary and secondary springs push the pistons back down the bore of the cylinder. The rapid movement of the pistons cause partial vacuums to form in the pressure chambers, which opens the centre valves and allows fluid to circulate unrestricted between the two hydraulic circuits and the reservoir. When the pistons reach the brakes off position, the centre valves are held open by the piston stops.