Posted by Doug Schubert on January 31, 1999 at 22:16:55:
In Reply to: e12 Brake Booster posted by Wietse Wullink on January 28, 1999 at 23:02:16:
: OK e12ers, here is another one.
: My baby is finally on the road after many months of blood (knuckles and head), sweat (getting rear trailing arms back into car after bushing upgrade) and tears (my brake frustrations), but I still don't have those great brakes I had before my mechanical restoration.
: Here is the current status:
: 1) New master cylinder
: 2) New SS brake lines
: 3) Rebuilt rear calipers (never install these backwards, right for left, it takes 2 weeks of bleeding brakes and cursing to figure out what you have done wrong! I will leave this story for another time.)
: Here is the operating conditions;
: Engine idles great, but after the first 30% of the brake pedal travel I can hear an audiable "hiss" inside the car and the idle changes (gets rough, like there is a vacuum leak). The brakes also do not have that "launch you into the dash" feeling and I can not lock up any of my wheels with full pedal pressure. I used to have brakes like this.
: First 30% of the travel, no issue and great power assist.
: Is this hiss normal? I don't remember this noise before I did all this work on the car. I checked the vacuum line, check valve and replaced the "o" ring at the vacuum line entry to the booster. No leaks there.
: Does this sound like a bad booster? Do you think there is a tear in the diaphram that only opens when stretched? Anybody go through this before?
: Any suggestions would be great. Also could someone verify that the hiss is either normal or not normal.
Sounds like maybe the brake booster, yes-if pedal
is hard and no "boost"-did you replace the maser
because it was bad? If they leak (as mine did)
into the brake booster it can ruin it-I know you
would hate to take the master off to look for fluid
in the booster but I bet you find it-my leaking one ruined
mine-got a used one 2 years ago from a 530i and has
been great ever since.........