Brake Servo Unit...Booster

[canada karl]

Hey Mike I need a memory refresh on what caused brake fluid to leak into the brake booster? Was it a leaky diaphragm? Is there a fix for this problem as I imagine internal parts would be impossible to find?

[canada karl]

Or is it motor oil that somehow finds it's way into the booster?

[Mike W.]

It's a bad master cylinder. IIRC it's a double seal there on the master, but it does happen occasionally that brake fluid can be pulled from the master into the booster since it's usually under vacuum.

So you need to rebuild or replace your brake master cylinder, then try to drain and perhaps clean out the booster, I'm not sure if the diaphragm is brake fluid rated.

[canada karl]

Thanks for the info.

[REman]

My 2 cents...when you have the booster out it's a great time to inspect the steering u-joint and replace if needed, along with any firewall pedal bushings.

[PatinaBeforePolish]

Or is it motor oil that somehow finds it's way into the booster?

I replaced the master cylinder at 195k and found about an ounce of what seemed like engine oil in the booster canister. I think that over time the 1 way valve in the vacuum hose to the booster had deteriorated allowing booster vacuum to draw fumes from the intake back to the booster which accumulated and settled in the reservoir. I replaced the valve, hose and master at the time (which I'm sure were original to the car) but haven't had a need to open it back up so this is only speculation.

[canada karl]

It does look like motor oil. Where did you buy the one way valve for the booster?
Reman...thanks for the tip.

[528i-1981]

I think they're readily available, but I bought one from Faulkner.
https://www.faulknerbmwpartssource.com/