The brake pedal on my 1989 190e2.6 sometimes goes to the floor. It will pump back up with two or three strokes. And then the brakes feel spongy. This happens only, so far it seems, after driving a few miles. In the morning brakes feel fine. So far !

There doesn't seem to be any fluid loss and so I thought I would replace the master cylinder.

Then I noticed the vacuum booster and wondered if that could be the problem ? Could the check valve on this be bad without fluid loss ?

Also the brake lines run into the ABS unit and I wondered about that. I have no data in my books on how to check the ABS unit.

Any help ?

Its your mastercylinder.

Did this happen all of a sudden or gradually. I had the same problem when I bought my 86 560sl. After flushing out the brake fluid all is fine. If flushing by pumping the brake pedal try not to push the pedal to the floor or you will be replacing the master cylinder. They build up a ridge that will tear the seals if they are pushed over the ridge.

The reason it seems to happen after driving a few miles is old brake fluid will have moisture. After you use the brakes a few times the water will boil and you will then have air bubbles that do not compress at the same rate as the fluid. Pumping the brakes overcomes this problem but not for long.

I let mine go for a couple of days but I do not recommend it. Changing the fluid is alot cheaper the repairing the front end.

I would take your email address out of your post unless you want spam. Add it to your profile instead if you want it available to members of this great site.

Thanks so much. I will do a total fluid bleed replace and see if that does it.

B

i dont think just bleeding will help.u probally have pressed the pedal to many times to the floor.like gschith sayed once u press to the floor u willl need a new master .and one thing to pay attention to is when u do replace the master look into the brake booster if there is any prake fluid in there.if there is remove all of it if possible.fluid from a leacking master cylinder.if u need help on bleeding than let me know