Re: return to list

["Fred Munro" <munrof@isys.ca>]

Hi Gemma;

    You don't mention what year and model Quattro you have, but the symptoms
sound like a bad brake "bomb" (pressure accumulator). The turbo cars were
fitted with a hydraulic brake boost system driven by a separate circuit on
the  power steering pump. The pressure accumulator holds enough pressurized
hydraulic fluid for ~30 brake applications if the engine is not running.
    Over time (about 7-9 years), the nitrogen charge in the bomb permeates
through the rubber diaphragm and the bomb will no longer hold pressure. When
this happens, hard braking depletes the pressure in the brake system (the
pump can't keep up) and you get a low pressure warning (red light and beep).
The car is dangerous to drive in this state, because a panic stop will
exhaust the boost pressure, resulting in no boost and significantly reduced
braking effect (unless you are a power lifter with thighs the size of tree
trunks, and large trees at that :o) If the ABS activates with a bad or weak
bomb, the boost can disappear instantly.
    You can test the bomb by running the engine until the red brake warning
light goes out, shutting off the engine, and pumping the brake pedal. Count
the applications until the pedal gets hard. A new bomb will give >30
applications. You should get at least 10.
    A new bomb costs about CDN$450 from the dealer and less from aftermarket
suppliers. They are relatively easy to replace, with the caveat to ensure
they are discharged by pumping the brakes at least 45 times before you open
any lines. Opening a highly pressurized hydraulic line can ruin your entire
day, not to mention your eyesight and other important body parts.
    Of course if your car doesn't have a bomb, you've read this rambling
dissertation for nothing :o)

HTH

Fred Munro
'91 200q  277k km (new bomb last year)

----- Original Message -----
From: Gemma Skillman <gskillma@usd.edu>
To: <quattro@audifans.com>
Sent: Friday, July 23, 1999 1:01 PM
Subject: return to list


> Hi everyone,
>
> I was on a 2 week driving vacation with my family and the quattro.  It
> was great to get away -- back to the eastcoast Toronto, NY, VT/NH--and
> saw many beautiful q's and a's.  While away I actually missed the "talk"
> on the listserve, and wondered whether people driving the q's and a's
> were list members.
>
> When I returned I had over 1400 messages!!!  I'm slowly trying to sift
> through them.
>
> On the trip the q ran beautifully, however an extremely annoying problem
> emerged on the first day.  The break light sensor and beeps would come
> on almost everytime the break pedal was pressed hard.  The breaks
> continued to work fine, however it was a pain to deal with the beeps in
> Chicago, Detroit, and Toronto summer traffic.
>
> My husband just took the car to the shop, and they said that some part
> that costs about $500 would need to be replaced near the engine. :-(
>
> Do you happen to have any idea what this problem could be?  And whether
> it is fixable in the home garage.  I imagine that my husband and I will
> double-team this project.
>
> Gemma
>
>
>