[PhaseP]

I replaced the check valve assembly hose and the rubber gasket last week. I have a 2006 e90, and I had this stiff brake pedal for a while. While under warranty I complained about it to dealership, they first changed the check valve hose assembly according to the SIB (TSB). It didn't fix it, I complained more, BMW center told them to change the brake booster altogether, didn't fix it either. After that they said it is the way these cars are, nothing we can do! I have a 2001 Corolla, it holds its brake vacuum even after days of sitting parked, same for a 2003 other car I have, how can it be normal! Anyway, recently the stiff pedal issue started to happen even minutes after shutting down the car. So it was leaking vacuum faster now. After reading this post, and not to leave anything to chance since I had been bothered with this so long, I bought a new vacuum hose with check valve, new rubber gasket, some flexible gasket maker RTV silicone (it is a blue one).

I used the instructions here, to gain access to the area. For removal of the old gasket, I suggest making something like a fish hook from a copper wire and place it in the gasket hole so that when it comes out you can fish it out of there. For placing the new gasket, I had trouble initially. My hands are wide and I could hardly touch the gasket area with my fingers. So I wrapped a loop with a thin copper solid hookup wire around the new gasket, on the thick lip part of it, not on the grove that goes into the hole in the brake booster. This way I could lower and position the new gasket with the wire from top of the engine with one hand, and push it in place with a long and big screw driver with the other hand. Before doing this, I had placed a small bead of RTV gasket maker only into the grove on the gasket that goes in to the hole.

After placing the gasket into the brake booster, again not being able to reach my hand in there effectively, I used a hex socket attached to a universal joint and then to an extension bar to push the check valve into the gasket. I used a socket big enough such that it fits to the had of the check valve.

The old gasket was exactly same as the new gasket I had bought. But I noticed brown dirt on all around the sealing grove on the old gasket, which was proof that it wasn't sealing properly, otherwise it would have no dirt in those places.

The new updated 2009 dated (at least once more) check valve assembly had a black head rather than the gray one. (which was already after the TSB, had 2008 date on it). The difference I noticed, the old check valve is one way, it allows air in one way, and blocks the other way. The new check valve does this same, but also if there is air pressure towards the brake booster, it lets this pressure to outside. The older check valve was working fine when I had tried to blow from each and of the pipe.

So the problem here is the gasket not sealing well as the OP brought to attention. I wish BMW could have figured this out, instead of replacing the whole brake assembly as an attempt to fix it.

It has been couple of days and my brake pedal is no longer stiff after car sitting down. And not only that, I immediately noticed the brake pedal response of the car got better. It became the same touchy/sensitive brake pedal like the way I remember it when it was brand new in 2006. So my leak was progressing by time that it was starting to effect even during driving.

Thanks again for your post, it allowed me to get rid of this long pesky problem!!