F 250 4WD HD Pickup V8-460 7.5L VIN G EFI (1997)
Vacuum Brake Booster: Description and Operation
Single Diaphragm Type
Power Brake Booster (Part 1 Of 2)
Power Brake Booster (Part 2 Of 2)
DESCRIPTION
A vacuum-type power brake booster is a partially sealed container. The interior 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.
OPERATION
Brakes Activated
As the brake pedal-to-power brake booster push rod moves forward, its motion closes the equalizer valve. This isolates chambers A and B. but
they are still under vacuum.
As the brake pedal-to-power brake booster push rod moves ahead farther, a port in the brake pedal-to-power brake booster push rod begins to line
