Grand Caravan FWD V6-229 3.8L VIN L MFI (1997)
Vacuum Brake Booster: Description and Operation
Power Brake Booster Assembly
DESCRIPTION
All vehicles use a 270 mm single diaphragm power brake vacuum booster. The power brake booster can be identified if required, by the tag
attached to the body of the booster assembly. This tag contains the following information: The production part number of the power booster
assembly, the date it was built, and who was the manufacturer of the power brake vacuum booster.
CAUTION: The power brake booster assembly is not a repairable component and must be replaced as a complete assembly if it is found to be
faulty in any way. The check valve located in the power brake booster is not repairable but it can be replaced as an assembly separate from the
power brake booster.
OPERATION
The power brake booster reduces the amount of force required by the driver to obtain the necessary hydraulic pressure to stop vehicle. The power
brake booster is vacuum operated. The vacuum is supplied from the intake manifold on the engine through the power brake booster check valve.
As the brake pedal is depressed, the power brake boosters input rod moves forward. This opens and closes valves in the power booster, allowing
atmospheric pressure to enter on one side of a diaphragm. Engine vacuum is always present on the other side. This difference in pressure forces the
output rod of the power booster out against the primary piston of the master cylinder. As the pistons in the master cylinder move forward this
creates the hydraulic pressure in the brake system. The different engine combinations used on this vehicle require that different vacuum hose
routings to the power brake vacuum booster be used. All vacuum hoses must be routed from the engine to the power brake vacuum booster without
kinks, excessively tight bends or potential for damage to the vacuum hose. The power brake vacuum booster assembly mounts on the engine side
of the dash panel, and is connected to the brake pedal by the input push rod. A vacuum line connects the power booster to the intake manifold. The
master cylinder is bolted to the front of the power brake vacuum booster assembly.
