E12 528i Brake Woes

[Eric Adair <eadair@xxxxxxxx>]

I have a 1980 528i. I purchased it three years ago for around $1200, and it
has served me well ever since, aside from assorted minor problems, all of
which the digest folks have helped me through.

Now, however, my brakes have failed, or at least 90% so. As long as engine
revs are high, I have plenty of brakes. When revs are low, the brakes
simply fade away until the pedal is near the floor and a bare minimum of
braking takes place. If, for instance, I apply the brakes sharply, there is
plenty of pedal and the car slows as normal, but if I continue to depress
the pedal, it sinks as the car slows, and braking force decreases. There is
plenty of fluid in the reservoir. The master cylinder was leaking about a
year ago, and was replaced with a rebuilt unit.

I have not had a chance to muck about under the hood much, as I have been
working, and it's approximately 800 degrees outside. Diagnosis-wise, I am
thinking vacuum generally, and more specifically I am thinking brake booster.

The booster for this car is available from Bavarian Autosport for the
miserly sum of $595, which is approximately $200 more than the value of the
car. The vehicle is generally worn out at this point, needing tires,
shocks, transmission work, a driveshaft rebuild, probably an engine
rebuild, paint, etc. I am not willing to sink loads of cash into this car,
which has become not-so-fun to drive, and which cannot have its fun
restored for less than several thousand dollars.

I will be purchasing a much newer BMW in the immediate future (I'm thinking
'95 540 or maybe an M3), so I'm basically hoping for a cheap fix that will
get this car stopping for at least the next few weeks, so that I might get
to work while I am arranging purchase of another vehicle.

To that end, I am fervently hoping for a response somewhere along the lines
of, "Oh yeah, I've seen that problem a million times, it's just a $5 check
valve". I've got little hope that this will be the response, but there is
always a statistical possibility. :)

Thanks in advance for any light you may be able to shed on my woes.

Eric Adair
1980 528i (declining)

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