[s-cars] Brake Light and Thrumming Pedal

brian hoeft qweblog at gmail.com
Fri Jun 30 17:06:27 EDT 2006 

On 6/30/06, Douglas Fifield <douglas.fifield at gmail.com> wrote:
>
> Brian,
>
> What do you have to do to get to the bolts that hold the servo in
> place?


first, i wish they were bolts,, theyre nuts, and i can laugh now because i
successfully did it, but i wanted to cry when i realized its difficulty
after pulling a used one(servo) from an urS i stripped that had everything
else out of it already..

3 nuts are easy, its the one(1) on top, most near the fuse box thats the
bitch of it all.  theyre attached in/through the firewall and require the
panels by your shins to be removed..  the servo has 4 studs you can visibly
see/touch in the engine bay to tease you.

in engine bay.. top right=bitch nut, in cabin, top left=bitch nut

i managed getting it off blindly by using my imagination,depth
perception,patience and prayer among other things..

theres a hole in the bedal bracket that i slid extentions and swivel joints
into to get at it while cerfully manipulating all the time.

replacing it depended on my friend that was holding the servo and directing
my movements while i manipulated the extention holing the nut at the end
against the hole in the firewall for which the stud was to go through.  then
i held in place waiting to feel the stud to begin setting the nut.



I assume that the complete brake system needs a full bleed
> afterward.  Is there a write up?


full bleed, yes, but that was welcome since i wanted to change fluid
anyways.  what wasnt welcome was snapping my first(rear passenger) bleeder
off...  thankfully a local machine shop was good enough to extract it
without hurting the taper it seats in.

write-up? not that im aware of, but i was thinking of putting words to my
pictures once i have get everything re-installed. just got the dell
drivers/utilities/etc while typing..

 One more question.  This sound that you mention - does it mean the
servo, or the bomb?

the servo.  the diesel like sound i mention went away once the new-to-me
servo was installed.


for now, //brian





On 6/30/06, brian hoeft <qweblog at gmail.com> wrote:
> >
> > sounds akin to my situation doug. the servo didnt leak profusely, and
> the
> > pedal was stronger than aahnold in the eighties with the first pump
> after
> > shutoff.
> >
> > soo,  the only other suggestion i have right now is to listen VERY
> carefully
> > for an audible diesel-like sound..  i was able to hear it relatively
> easily
> > in the cabin.  of course you should have your vents and radio off being
> as
> > quiet as possible and just be very alert.
> >
> > remember, diesel-like-sound... :]   .. if i remember correctly the sound
> > fluctuated a bit when touching the vibrating pedal.
> >
> > hopefully this is not the case and it is your accumulator.  much much
> easier
> > to replace and muchmuchMUCH cheaper, or swap the emphasis because the
> servo
> > was a borderline nightmare for me to replace.
> >
> > best wishes, //brian
> >
> >
> >
> > On 6/30/06, Douglas Fifield <douglas.fifield at gmail.com> wrote:
> > > Fred and Everyone Else,
> > >
> > > Pushed the car out of the garage this morning, raised hood, had #1 son
> > > start engine while I watched G002000 level in resivoir.  It was above
> > > the full mark at about the seam level around the top of the tank.  It
> > > did not move discernably the whole time the engine was running.  Brake
> > > light was on and brake pedal thrumming.  Turned engine off and brake
> > > pedal was rock hard.  Resivoir level never changed.
> > >
> > > What does this tell us?  I will try to find the materials to do the
> > > servo leak test, but I don't have those materials readily available.
> > >
> > > D.
> > >
> > > On 6/29/06, Fred Munro < munrof at sympatico.ca> wrote:
> > > > Douglas;
> > > >
> > > > Do the reservoir drawdown test I detailed in my earlier post. If the
> > bomb is OK and the servo is leaking, the pump will partially charge the
> bomb
> > and pull oil out of the reservoir with the engine running. Once you stop
> the
> > engine, the oil will leak back out of the bomb through the servo and
> fill up
> > the reservoir. If this happens, you'll have to test the servo to isolate
> it
> > as the cause. This leak will be too large to do the Bentley servo test.
> You
> > should use a test rig similar to what I described.
> > > >
> > > > If the bomb has failed, the pump will not put much oil into it and
> the
> > level in the reservoir won't change much.
> > > >
> > > > Fred
> > > >
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: Douglas Fifield [mailto: douglas.fifield at gmail.com]
> > > > Sent: June 29, 2006 4:24 PM
> > > > To: Fred Munro
> > > > Cc: s-car-list at audifans.com
> > > > Subject: Re: [s-cars] Brake Light and Thrumming Pedal
> > > >
> > > >
> > > > Fred et al,
> > > >
> > > > Things have progressed on the brake problem front.  Now, as soon as
> I
> > > > turn off the engine, the brake pedal goes rock hard.
> > > >
> > > > I am not sure if this means the bomb has failed, or if the servo is
> > > > leaking so badly that the bomb cannot be pressurized.
> > > >
> > > > Any thoughts?
> > > >
> > > > D.
> > > >
> > > >
> > > > On 6/28/06, Fred Munro <munrof at sympatico.ca > wrote:
> > > > > Douglas;
> > > > >
> > > > > The bomb has depressurized overnight. The brake light is on to
> warn of
> > low
> > > > > pressure in the brake boost system. The thrumming brake pedal is
> > caused by
> > > > > the pressure pulses from the positive displacement hydraulic pump.
> > When you
> > > > > apply the brakes with no stored pressure in the bomb, the boost
> > pressure
> > > > > comes from the pump and you feel the high and low pressure pulses
> as
> > > > > vibration in the brake pedal.
> > > > >
> > > > > The bomb discharges due to a leaking check valve in the bomb or a
> > leaking
> > > > > brake servo. I used to believe the bomb check valve was the usual
> > culprit,
> > > > > but I now suspect the servo is usually at fault. The servo can
> leak by
> > so
> > > > > badly that the pump will never built up enough pressure to turn
> off
> > the
> > > > > warning light - I just had this problem in my '97 S6. If your
> warning
> > light
> > > > > doesn't go off, this is most likely your problem. A bad bomb check
> > valve
> > > > > will not prevent the bomb from pressurizing to design pressure.
> > > > >
> > > > > Flushing the central hydraulic fluid sometimes corrects the
> problem.
> > Clean
> > > > > the strainer in the reservoir when you flush the fluid.
> > > > >
> > > > > You can determine if you have a bad servo or check valve leak by
> > running the
> > > > > engine and noting the level in the reservoir. Shut off the engine
> and
> > watch
> > > > > the level. If you can see it visibly rising, either the servo is
> toast
> > or
> > > > > the bomb check valve is leaking badly. To test the servo, run the
> > engine to
> > > > > charge the bomb. Stop the engine. Remove the RETURN line on the
> servo
> > (the
> > > > > top connection). If more than a few drops of oil leaks out, the
> servo
> > is
> > > > > kaput. If you can see the fluid level rise in the reservoir, this
> test
> > is
> > > > > not a good one for two reasons:
> > > > > 1. By the time you get the return line off, all the pressure has
> > leaked out
> > > > > and no oil will be released.
> > > > > 2. If you do get the line off in time, so much oil will come out
> > you'll have
> > > > > it all over the rack and the driveway.
> > > > >
> > > > > I built a test rig to test my servo. I discharged the bomb
> completely
> > by
> > > > > pumping the brakes and removed the servo return line. I clamped
> off
> > the
> > > > > rubber section of the return line with a brake hose clamp. I bent
> a 8"
> > > > > section of pre-made metric brake line at 90 degrees and threaded
> one
> > end
> > > > > into the return line port. I attached a plastic hose on the other
> end
> > and
> > > > > ran the hose into a jar. Start the engine (do NOT apply the
> brakes!!!)
> > and
> > > > > watch the plastic line. A flow of oil indicates a leaking servo.
> On
> > the '97
> > > > > the oil flow was a steady stream - the servo was completely shot.
> > Funny, the
> > > > > car had just been certified too. That explained why the warning
> light
> > was
> > > > > disconnected......
> > > > >
> > > > > HTH
> > > > >
> > > > > Fred Munro
> > > > > '97 S6
> > > > > '94 S4
> > > > >
> > > > > -----Original Message-----
> > > > > From: s-car-list-bounces at audifans.com
> > > > > [mailto: s-car-list-bounces at audifans.com]On Behalf Of Douglas
> Fifield
> > > > > Sent: June 28, 2006 9:27 PM
> > > > > To: s-car-list at audifans.com
> > > > > Subject: [s-cars] Brake Light and Thrumming Pedal
> > > > >
> > > > >
> > > > > Hedz,
> > > > >
> > > > > We have been over this one before, but I keep hoping that someone
> will
> > > > > have figured it out and give me a clue.
> > > > >
> > > > > On and off, my S6 has had periods where the brake light stays on
> > > > > beyond the normal 20 or so seconds in the morning.  These sessions
> > > > > have been accompaning by a thrumming brake pedal and as long as
> that
> > > > > continues, the brake light stays on.  In the past, the thrumming
> would
> > > > > eventually stop and a few seconds later, the light would go out.
> > > > > Today, it stayed with me and now the car is in the garage.
> > > > >
> > > > > It seems to stop normally.  Just had the brakes flushed last week
> and
> > > > > the fluid levels are good.
> > > > >
> > > > > Any ideas?
> > > > >
> > > > > --
> > > > > Douglas in MN
> > > > > 95.5 Audi S//6 Avant
> > > > > 73 BMW R60/5 mit Toaster Tank
> > > > > _______________________________________________
> > > > > S-CAR-List mailing list
> > > > > S-CAR-List at audifans.com
> > > > > http://www.audifans.com/mailman/listinfo/s-car-list
> > > > >
> > > > >
> > > >
> > > >
> > > > --
> > > > Douglas in MN
> > > > 95.5 Audi S//6 Avant
> > > > 73 BMW R60/5 mit Toaster Tank
> > > >
> > > >
> > >
> > >
> > > --
> > > Douglas in MN
> > > 95.5 Audi S//6 Avant
> > > 73 BMW R60/5 mit Toaster Tank
> > > _______________________________________________
> > > S-CAR-List mailing list
> > > S-CAR-List at audifans.com
> > > http://www.audifans.com/mailman/listinfo/s-car-list
> > >
> >
> >
>
>
> --
> Douglas in MN
> 95.5 Audi S//6 Avant
> 73 BMW R60/5 mit Toaster Tank
>

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