9000 L4-2290cc 2.3L DOHC (1991)
Vacuum Brake Booster: Description and Operation
DESCRIPTION
Fig. 1 Internal View Of Master Cylinder
The servo (booster) unit Fig. 1, provides power assistance to the pedal effort applied. The servo obtains its power from vacuum created in the
engine inlet manifold and provides assistance in a ratio of about 4 to 1. Should a vacuum failure occur, the two pushrods will act as a single rod,
allowing brakes to work conventionally but with a much greater pedal effort.
OPERATION
When the brake pedal is depressed, then input rod pushes the control piston and diaphragm forward, closing the vacuum port. As the input rod continues
to move forward, the control piston opens the atmospheric port, allowing atmospheric pressure to enter through the filter and into the rear shell behind
the diaphragm.
Since vacuum is still present at the front of the diaphragm, the pressure assists the input rod in pushing the diaphragm forward and the output rod to
actuate the master cylinder.