Section 06-00: Brake System, Service | 1996 F-150, F-250, F-350, F-Super Duty Chassis Cab, Motorhome Chassis and Bronco Workshop Manual |
A vacuum-type power brake booster is a container whose inner space is divided by a diaphragm into two separate chambers — A and B. The brake pedal-to-power brake booster push rod enters on one side, and the brake master cylinder push rod exits on the other. The brake master cylinder push rod is attached to the center of the diaphragm.
There are three valves that control the vacuum in the power brake booster. The power brake booster check valve opens to allow the intake manifold vacuum to evacuate the power brake booster. When it closes, it holds the vacuum in the chambers.
The equalizer valve links the two chambers. When it is open, the vacuum in the chambers can equalize. When it closes, the chambers are separated.
The vacuum bleed valve functions to reduce the amount of vacuum in chamber B when boost is required. Refer to Section 06-07A for more detail on how boost is produced.