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New 5kcstq intro and HELP!

Hi All,

I've been hanging out here on the list for a while, and have posted then and
again.  I was here long enough to become convinced I could not go through
life without a 5kcstq.  Thus, Monday night I purchased one in Walnut Creek,
CA, had it checked out by M&M Audi Haus, decided to keep it, and started my
13 hour drive back to Woodinville, WA Tuesday afternoon.  I made it without
tire chains :-)

The bad news is the car is decidedly funny with the brakes.  The car has a
replaced used bomb.  As near as I can tell the bomb is not the issue.  What
happens is that as you stop for a traffic signal on a hill, for instance,
the car behaves normally.  It stops.  As you wait at the signal with the
brake continuing to be depressed, the pressure slowly goes away on the
pedal.  If you push harder or further, the brakes continue to hold.  This
tells me the master and slaves are not the issue -- after the system has
lost pressure once, it holds forever.

Ok, the good news is the car came with a set of Bentley manuals.

Section 45 talks about a test for the Hydraulic Modulator -- a pressure
test.  From the behavior I am getting, this test is essentially what you do
when you stop and wait for a traffic signal, and I fail it by loosing
pressure.  Solution to any problem with the Hydraulic Modulator is replace.
Anyone have a '86-'88 5kcstq (has to be a 5kcstq, I believe, from the
Bentley) they are willing to part out?

Now it is also interesting that the ABS cutout switch on the dash does not
work; it does not activate the ABS Off light.  A replacement known good
switch changes nothing.  Switching on the car shows the ABS Off light on;
starting the car extinguishes the ABS Off light.  Switching on the diff
locks activates the ABS Off light.

A quick skid test shows the ABS system non-operational.

Help, what do I do now?  Is the modulator likely the problem?  Is there any
diagnostic _I_ can do on the ABS brain.  The remaining 95% of section 45
talks about using the factory tester, which I don't happen to have.  Any
suggestions on how to proceed in debugging the brake problem are

The 5kcstq has a few other problems too, but this one is the most immediate.
Just warning you all you'll hear from me again :-)


Bernard Littau
Woodinville, WA
'88 5kcstq