Brake fluid in booster.

[polloelastico]

I just removed my brake booster, which was in itself an awful task (what is up with that lower outer 13mm nut? Is that some kind of sick joke by bmw?). Anyway, after triumphantly pulling it out, I was rewarded with a shower of brake fluid; seems the MC is leaking in there.

I plan on replacing the MC anyway, which is why I took it out. Well, okay, I took it out to paint it because, dammit, it just wouldn't look good next to that new MC!

Anyway, should I be alarmed about this, or just assume the new MC o-ring will take care of this.

Oh, as a bonus, I had to cut a couple hard lines off since they were totally rusted to the MC (anyone *not* make a sucky flare wrench?).. guess I'll be replacing those as well right now....

[ingraham]

A note to anyone who is losing brake fluid and can't find the leak: P.E.'s lesson is a good one. To find a leak:

1. Check the brake calipers and lines.

2. Check the rear wheel cylinders and lines (drums off).

3. Check the clutch master cylinder (under the carpet), slave cylinder, and lines. Peel back the boot on the clutch MC.

4. Check the brake master cylinder and lines.

5. Finally, undo the two nuts holding the MC to the booster, pull the MC forward a bit, and peer into the booster with a good light or a dipstick. A lot of fluid can hide in the booster.

In case 5, siphon and mop out the booster and put on a new brake MC.

[FL02]

I had a similar issue with a brake master cylinder going out and I got a used master cylinder and booster that I installed together. My booster just went and I put on the old one and it works real good, better than the other one, so it's just the MC leaking and probably no problem with the booster. Just dump it out, respray it, and replace wth a new master cylinder and it should be OK.

[jimk]

BTW it probably was not the oring, it was the outer MC shaft seal. The oring keeps air from sucking in.

There are 2 seals an inner which holds the high pressure and the outer which keeps brake fluid from running along the shaft into the booster. In between the 2 there is a hole on the bottom of the MC. That's where the leakage is supposed to go (and it burns the paint on the front of the booster as it dribbles down on the frame too).