Power Brake Booster

DESCRIPTION






All 1500 & 2500 gas engine vehicles are equipped with a tandem (dual) diaphragm power brake booster. Three versions are used.
- 1500 model with 245 tires and smaller
- 1500 model 265 or 275 17 in. tires
- 2500 model with gasoline engine
The booster assembly consists of a housing divided into separate chambers by two internal diaphragms. The outer edge of each diaphragm is attached to the booster housing. The diaphragms are in turn, connected to the booster push rod.
Two push rods are used to operate the booster. One push rod connects the booster to the brake pedal. The second push rod (at the forward end of the housing), strokes the master cylinder pistons. The rear push rod is connected to the two diaphragms in the booster housing.
The only serviceable power brake booster components are the vacuum hose and check valve. The booster itself is not a repairable component. The booster must be replaced as an assembly whenever diagnosis indicates a fault has occurred.

OPERATION
The atmospheric inlet valve is opened and closed by the push rod connected to the brake pedal. The booster vacuum supply is through a hose attached to a fitting on the intake manifold. The hose is connected to a vacuum check valve in the booster housing. The check valve is a one-way device that prevents vacuum leak back.
Power assist is generated by utilizing the pressure differential between normal atmospheric pressure and a vacuum. The vacuum needed for booster operation is taken directly from the engine intake manifold. The entry point for atmospheric pressure is through an inlet valve at the rear of the housing.
The forward portion of the booster housing (area in front of the two diaphragms), is exposed to manifold vacuum. The rear portion (area behind the diaphragms), is also under vacuum, but less vacuum then the forward portion.
Pressing the brake pedal causes the rear push rod to open the inlet valve. This exposes the area behind the diaphragms to atmospheric pressure. The resulting force applied to the diaphragms is what provides the extra boost in apply pressure for power assist. Pressure differential creates force imbalance and provides boost.