Brakes off
In the rest position (brakes off), the force applied by the
return spring presses the diaphragm and plunger back to the rear of
their travel. Because the diaphragm overflow valve is open, equal
vacuum pressure will be present on both sides of the diaphragm,
and the return spring in the master cylinder will be moved towards
the rear of its travel. In this position, the central valves in the
primary and secondary circuits are open and the brake system is
pressureless. A stop pin prevents rearward movement of the
secondary plunger, and a spring washer rearward movement of the
primary plunger.
The master cylinder and other hydraulic components are
charged with brake fluid that is not pressurized.
The inlet and outlet valves in the valve block are in the rest
position.
