Brake Booster Loosing Vacuum
 

Brake vacuum booster leaking on 98 W210 ?? When you step on the brake before you start the car the pedal is dead hard (no power boost). To me this indicates that the booster has lost it vacuum. to check this I attached a vacuum gauge to the line going into the booster. it read 15 inches with the engine running. as soon as i turned it off the vacuum slowly went to zero. i tested the inline valve and it does not appear to leak. has anyone else run in to this? I don't know what else to test or do. I don't know how to tear into the boosters. any suggestions