Ranger 4WD V6-3.0L VIN U (1997)
Power Brake Booster Cutaway (Part 1 Of 2)
Power Brake Booster Cutaway (Part 2 Of 2)
FUNCTION
In vehicles powered by gasoline engines, vacuum-type power brake boosters make use of the vacuum produced in the intake manifold to apply
additional force to the master cylinder push rod. A vacuum-type power brake booster is a container whose inner space is divided by a diaphragm
into two separate chambers. The brake pedal push rod enters on one side, and the master cylinder push rod exits on the other.
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.
The Brake Pedal 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 push rod moves farther ahead, a port in the brake pedal push rod begins to line up the ports in the sleeve. This vents
chamber B to the outside and reduces the amount of vacuum in chamber B. With more vacuum in chamber A and less in chamber B, the
diaphragm is forced forward in the direction of the master cylinder push rod, providing a boost.
The Vacuum Bleed Valve - is not just an open/close valve. A spring located at the forward end of the brake pedal push rod allows the push rod
and the sleeve to slide back and forth in relation to each other as the brake pedal is activated. This opens and closes the vent in such a way that
only the required amount of vacuum is drawn on. Hard braking bleeds off more vacuum, producing more boost. Light braking generates less boost.
Once the level of boost corresponds with the applied brake pedal force, the bleed valve closes and holds that level.
