Legacy Outback Limited AWD F4-2.5L DOHC (1998)
4. Brake booster under full-load conditions.
When pedal depression increases to such an extent that the variable-pressure chamber is maintained at atmospheric pressure, the maximum
pressure differential acts on the diaphragm plate.
Further pedal depression does not act on the diaphragm plate but rather on the push rod.
5. Brake booster released.
When the force of brake pedal depression decreases, the forces acting on the reaction disc and plunger valve are unbalanced, so that the plunger
valve is moved to the right.
The plunger valve then comes in contact with the atmospheric valve of the poppet valve to shut off the passage between the variable-pressure
chamber and atmospheric air and, at the same time, moves the poppet valve back. Movement of the poppet valve opens the vacuum valve so that
passages A and B are linked with each other.
Air from the variable-pressure chamber is then delivered to the constant-pressure chamber. This eliminates any pressure differential between the
two chambers. As a result, the diaphragm plate is pushed back to the "release" position by the return spring.
