[s-cars] bomb time

Mon Jan 23 06:02:32 PST 2012

Tom/Brian,

I will reread all the info provided in Tom's email and the links before
going forward, but as my comments were just asides to the query on the bomb,
let me be more specific.

First, the brake light comes on when started after having sat for a day or
more, and goes off fairly quickly.  It does, however, come on at other
times, more often lately, when the car has been driven and then been parked
for a shorter period of time, like a couple of hours.  During those times,
the light does not go off as readily, and it is during those times during
short rides back to the house that it stays on more and that I have noticed
the brakes squealing at the times the light comes on during light braking
over the short, in town drives home.  Not an issue coming off the
interstate.

The system was flushed back not quite two years ago (when was it Tom?) when
the steering rack required replacement after the kid had first sprung a leak
and blown a HP hose while driving it to HS his senior year.  Since he is in
the middle of his sophomore year in college, it actually must be that long.
Last time I checked, everything was still nice and clean, but crud could
easily have been dislodged back then and made its' way through the system.
However, I think that Jorgen provided an inline filter with the replacement
rack.  

Also, my mechanic made a comment about the bomb going bad last summer when I
actually let him flush my brake system.never any time anymore.because he
thought it was bleeding off pressure when he shut it down and had it sit for
part of the day before doing something else on the car.  And Tom, you are
right, Paul is out of accumulators, but I will be dealing with him as soon
as I start a new job, after being out of work/consulting since August, and
will be bringing over one of his exhausts for the car.  The Magnaflow cats,
center and rear mufflers in my patched exhaust system is just too freakin'
loud and droning.  I will be taking the car to my mechanic for some other
work once the paychecks start coming in again, and planned to have him test
the pump output before going forward.  In any case, I last replaced the bomb
while I was living in Louisiana.  We left over a year before Katrina, and I
think it is probably 9+ years old.  It would be the third bomb for a 17 year
old car, so not bad.

Thanks for all the advice.   Tom, you have been consistently more
knowledgeable and informative than any mechanic I've found near me in Katy,
TX.  Might have to head up to Tomball and drop the car off with a fellow
lister and see if he can sort things out with it sometime down the line.
It's unlikely we'll ever take the S6 up to Knoxville to visit my
sister-in-law now that the wife has her Touareg, so I can't get you to  give
it a premier once over.

All the best,

Steve

From: brian hoeft [mailto:qweblog at gmail.com] 
Sent: Sunday, January 22, 2012 10:14 PM
To: Tom Green
Cc: s-car list; Steve Marinello
Subject: Re: [s-cars] bomb time

Very informative Tom, good reads for Steve, I was just going to say it
sounds more like he has a leaky caliper or MC and should check his brake
fluid...

On Sat, Jan 21, 2012 at 7:47 PM, Tom Green <trgreen at comcast.net> wrote:

The classic bomb problem is the failure to retain system pressure when the
engine is shut off.  This shows itself as the brake light remaining on after
start for ~30 seconds.  That is the only function of the accumulator-retain
sufficient brake pressure for emergency use when the engine is off.   When
the engine is running and the pump has had time to charge the bomb to full
system pressure, it does not really come into play unless you make very high
demands that the pump can't supply and/or there is some other problem as
well. So, you may need a bomb, but probably something else as well.

That could be a system flush and filter cleaning or some more hardware.
Check out the FAQ at the UrS4/6/S2/RS2 forum on Quattroworld.com then don't
ask questions until you have looked here.  : )   If the light is on at every
start, probably plan on a bomb, but start by looking at the fluid in the
hydraulic reservoir.  Check for a bright, clear olive green color;  pull the
little plastic sleeve with the screen that drops in the reservoir fill hole.
The screen should be bright steel.  If it is black, that is rubber from
seals and hoses.  Black fluid and filter means cleaning and flushing is
overdue.  I recommend putting a 3/8" Magnefine filter in the return line
also.  I would do this cleaning/flushing/fluid change before deciding what
is broken from the troubleshooting discussed below.  It could just be junk
blocking flow through the screens in the banjo bolts or reservoir and/or
keeping a check valve in the bomb or servo from closing fully.

The only problem with this troubleshooting procedure is without a pressure
test on the pump output to the brakes, you don't know if a weak pump output
is causing or at least contributing to the problem.  If the servo leaks,
that could be the only problem, but you can't really tell if the system
won't hold pressure so you can test the other parts.  An extra part or two
would be no big deal for a system that has this age on it, but these are
expensive parts.

This is the place to start in the FAQ:

http://members.shaw.ca/speedtek/UrS%20chassis%20Map.html

And, this is the section to troubleshoot your system to determine where to
start, and it is not go buy a bomb:

http://www.elektro.com/~audi/audi/hydraulic.html
<http://www.elektro.com/%7Eaudi/audi/hydraulic.html> 

Here is another source for accumulators;  Unfortunately, he is out of stock:

PARTS FOR AUDI C4 CARS (100 / S4 / A6 / S6 & S6 PLUS)

The squealing brake is a brake problem, not a hydraulic boost problem.

Cheers,

 Tom '95 S6
        '95.5 S6 avant
Knoxville, TN

OnSaturday January 21, 2012, at 1:05 PM, "Steve Marinello"
<smarinello at entouch.net> wrote:

I expect to be needing a new bomb shortly, as the light now comes on
at.interesting times.  One observation.when it comes on during braking from
relatively slow speeds, the brakes squeak.reduced clamping force?  I'll
check to see if Dave Kase is still recharging them, but I was wondering if
anyone knows much about where the new ones are being made.  WOrldPac has
Febi Bilstein bombs and there are a couple of sources with Meyle units,
including GR on ebay.  I'm guessing the Meyle ones are definitely Chinese
now; anyone know about the Febi's?  There's about a $45-$50 price
differential.

TIA,

Steve

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-- 
       -Brian
      [blinders off&ear <http://208.53.138.125:8068/> plugs out]