Brake Booster leak?

[mobilenemo]

Hey Guys,

Replaced the rear rotors, pads, upgraded all brake lines to stainless steel and bled the fluid using the 2 person method. With engine on, brake pedal feels mushy off the top and I can trigger the vacuum pump by pressing the brakes hard (3-4 times to build pressure) pausing and pressing the brakes hard again will trigger the vacuum pump.

Poking around for leaks i find yellowish fluid around the piston rod for the brake master cylinder see attached photo. I assume it's brake fluid (might be wrong) and wondering if it is normal or a bad master cylinder?

Other than the soft pedal off the top and the frequent vacuum pump coming on, the car drives normal and I can trigger ABS on hard stops.

Any insight is appreciated! Thanks

[Redd]

I had mushy pedal previously. Changed master cylinder which helped a bit but was still mushy. In the end I changed the brake booster and it was solved.

[mobilenemo]

Just an update on this issue, replacing both master cylinder and booster solved it.

[E90_slides]

Did you also have reduced mpg and engine running rich? Mine is leaking into cabin as well and I think the booster has a vacuum leak, but the vacuum pump helps enough to assist the brakes without the leak causing no assist at all. I got everything smoke tested besides the booster, they claimed it was too difficult to get to. So I literally changed pretty much every sensor and part that I could. O2 injectors spark plugs vanos solenoids coil packs gaskets fuel pump and regulator and many more parts and still no change.

[mobilenemo]

Can't say I noticed a change in the MPGs after replacing the booster and master cylinder

[Scrippy]

So when I sit at stop lights with the brake pedal depressed it has an effect on my idle. If it’s level and I have the ability to let off the brake without moving the idle is perfect. Think I may have a similar issue as OP? No error codes or anything and no braking issues. Pedal feels great.

[Ximian]

Originally Posted by Scrippy

So when I sit at stop lights with the brake pedal depressed it has an effect on my idle. If it’s level and I have the ability to let off the brake without moving the idle is perfect. Think I may have a similar issue as OP? No error codes or anything and no braking issues. Pedal feels great.

Generally speaking when the depressing the brake pedal affects idle RPM, something is up with your brake booster. Unfortunately there is a wait to get a new brake booster from Germany at the moment, about 6 weeks.

If you have some fluid residue on the brake booster diaphragm area, it's generally a brake booster issue. Initially I thought it was an o-ring or other type of seal since I had a similar thing. There is a big o-ring on the master cylinder where it looks like it would seal when connecting to the brake booster, but that's unlikely to fix it since mine was in excellent shape. It's some sort of internal booster damage that I couldn't find.