[s-cars] HELP! again...

[Fred Munro]

Hi Joe;

There are two aspects to this problem.

The first is "Why is the light coming on at cold start-up?". You've got a
pressure leak somewhere that is allowing the pressurized fluid stored in the
bomb to leak back into the reservoir. When you start the car, the pump has
to re-pressurize the bomb and the light stays on until the pressure is up to
the lower limit on the pressure warning sensor. The usual leakage culprits
are the internal check valve in the bomb and the brake servo mounted behind
the master cylinder. Since you have a new bomb, the servo is the likely
culprit (assuming the bomb is good from the factory - this can be a bit of a
stretch sometimes). The check for the servo is to remove the return pipe to
the reservoir and check to see if oil is flowing out of the port. A few
drops is OK, but any kind of flow will discharge the bomb over time. This
was an easy check on the Type 44 because the return line was a hose, but I
think the UrS is a hard piped line. Check the Bentley before doing this -
removing the wrong line here can ruin your entire day, not to mention the
potential injury and disfigurement from a shot of 2000 psig oil in the
kisser (got your attention yet?). The safe approach would be to discharge
the bomb, remove the line, and recharge the system. That way opening the
wrong line would spray Pentosin all over your engine compartment, run the
pump dry, and burn it up - but your boyish good looks would be intact!

But I digress.

The other half of this issue is "Why is the light on for so long and longer
when it is cold?". It's taking time for the pump to recharge the system. Oil
is thicker when it is cold. This argues a restriction in the system. Pull
the screen from the reservoir (you don't have to drain the Pentosin, but it
doesn't hurt) and thoroughly clean the screen with solvent. Remove some
Pentosin and check the colour. If it has been flushed as often as your
mechanic says, it should be a clear green colour. If it is dark or black, it
needs changing. Replace the screen and see how the system works. If it still
takes a long time to charge up, try replacing the banjo bolts on the high
pressure hose. These have small screens inside - it's easier to replace the
bolts than to clean the screens.

I solved this problem on my UrS4 by changing the Pentosin and cleaning the
reservoir screen. Now I don't get the light even after the car has been
sitting for several days. Previously I was getting the light after it sat
for several hours and it would take 40 seconds or so for the light to go
out.

HTH Joe! Good luck!

Fred Munro
'94 S4


-----Original Message-----
From: s-car-list-admin at audifans.com
[mailto:s-car-list-admin at audifans.com]On Behalf Of Joseph Pizzimenti
Sent: September 29, 2002 10:48 PM
To: s-car-list at audifans.com
Subject: [s-cars] HELP! again...


Guys-
Here we go again.  I just replaced the PS pump, hp
hose from pump to bomb, the bomb itself, left rear
caliper and I STILL FRIGGIN HAVE TO DEAL WITH THE DAMN
CURSED BRAKE WARNING LIGHT ON COLD FRIGGIN DAMN
STARTUP!  Okay, now that I've vented, maybe someone
can point me in the right direction here.  Pentosin
has been flushed to hell by mechanics, or so I'm told.
 Anyone else mind telling me what I'm missing here?
Bomb should be fine, as that's new.  I want to drain
the pentosin and check the screen in the reservoir
just to be fine and dandy.  What else can cause that
light to stay on?  It does it longer when it's been
cold out, sometimes it doesn't happen at all.  What
gives?
Help?

Thank you all,
Joe "If it ain't one thing, it's another" Pizzo

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