Vacuum Booster Check Valve — Check (Nissan Bluebird T12)

1. When checking the booster unit check valve, remember that air should only flow out of the unit in one direction. If air flows in both directions or neither, the valve is faulty and should be replaced.

2. To check the valve, blow into it from the side of the vacuum booster unit (square end); air should flow freely through the valve. Now suck from the same end; there should be no air leakage through the valve.