brake "bomb": how to pick one at the scrap yard?

South African Audi 500, 1989 (same as Audi100 type 44 in Europe/USA)

Hi again,

I have the following problem: I finally figured out that my brake
accumulator (the "bomb" mentioned so often) is not working either. I
always suspected that the breaks didn't work as well as they should
when pressed suddenly, but after I read the infos on sjm and in other
places, I am sure it's the bomb. When the engine is running, the break
pedal can be pressed down, but there is a brief delay and then it
moves further down. With the engine off, there is no more action.

The local audi dealer wants the equivalent of US$ ~500 for a
refurbished one, which is far beyond what I want to spend on it now.
There don't seem to be any other sources in South Africa and when I
spoke to a power steering repair place, he said the only alternative
was the scrap yard and that a lot of those would be around there. I
asked him how I could know whether I pick up a good or bad one, but
his only reply was "bring it along, we will put it in and tell you"
Scrap yards here take things back and return the money, so that's not
the problem. However, I would have to do quite some driving to get to
the nearest one and I don't want to change around break bombs until I
find a good one.

With no MOT here and generally little regard for safety, it is very
likely that a lot of the break bombs on old Audis don't work any more.
To be honest, it took me some time to figure out that I have a
problem.

My question: Is there any way I can see on the scrap yard whether I
get one which is still ok or whether it is gone as well? I understand
that there is a gas reservoir under pressure in there which looses
gas. Is there any way I could look into the bomb to see whether the
divide is still at the right place, or push a wire or little stick in
or anything else?

Or is there maybe any way to distinguish between a factory refurbished
and an original one? If it is refurbished, there is a good chance that
the owner had it replaced not too long ago?

One more question: How compatible are they over the years? Can I get
one from a younger car and still put it in, or is this asking for
trouble?

Thanks a lot for your help,

Christoph

P.S. I am still busy with the speedometer. I got quite a bit further
and will post the final results as soon as I get it all done. Just one
hint for now: Twisting the needle counter-clockwise did the job to get
it off.

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