A vacuum booster uses vacuum pressure from the engine to boost the amount of pressure going to the brakes. The check valve on vacuum booster regulates the amount of pressure in the booster. If the valve is malfunctioning, the booster will produce an insufficient amount of pressure to the brakes.
Locate check valve. The check valve is generally located where the vacuum line from the engine connects to the booster.
Remove any clamps holding vacuum line to the check valve, then remove the vacuum line.
Using wrench or screw driver as needed, remove check valve. Apply 15-20 hg of pressure to input end of the valve using the hand held vacuum pump. The valve is faulty if the pump shows any pressure loss.
Install new check valve onto booster. Re-attach vacuum hose to check valve. Use clamps if necessary to hold valve or hose in place.
Start the engine. Check brakes to be sure they now have good pressure. If the pressure still seems wrong, you may have a bad brake booster.
