Posted by Paul on April 04, 2000 at 22:07:23:
In Reply to: Squishy pedal posted by Dan on April 04, 2000 at 13:04:46:
{{I have a '79 w200. When i press the brakes wiht the engine off, they work fine, but with the engine running the pedal gets REAL soft and goes all the way to the floor without stopping the truck (very bad thing). I've redone all 4 wheels, bled and adjusted the hell out of them. Any Ideas? }}
Are you losing any brake fluid? You may have a pinhole leak in the booster. However, before you tear into that puppy, first off check your calipers and make sure they are on the correct side. If you get them swapped, the bleeder will be below the air bubble and it won't come out. Another possiblity is a partially disintegrated brake hose that is expanding under pressure.
Another possiblity is the master cylinder is leaking but not much without the boost. With the boost, you're just smashing the fluid past the seals.
I would #1, check the calipers to see if they are on the correct sides. #2 pull the vacuum supply hose off the intake and check the inside for brake fluid. If there is some in there, you have a leak in the booster. #3 Check all 4 flexible hoses. There should be one at each front wheel, one from the frame to the front axle, and one from the frame to the rear axle. If they are dry rotted, replace them immediately.