[s-cars] Brake Light and Thrumming Pedal

Tue Jul 4 15:27:37 EDT 2006

Happy Fourth everyone.  I am spending mine laying on my back looking
up under the dash and wondering how in the hell am I going to get at
those 13 mm nuts.

First, I can't see them.  I see the servo push rod where it comes out
and connects to the brake pedal, but there is some sounddeadning foam
pasted up against the bulkhead hiding the nuts from view.  I can't get
a hand up there to try to move it.

There are a couple of air ducts that go from side to side in the work
area and it would be easier to access I think if the lower duct could
come out.  Brian, Fred, did you have to remove bits and pieces to get
at the nuts?  If so, do you remember what and how?

Curious minds wish to know.

D.

On 7/3/06, Fred Munro <munrof at sympatico.ca> wrote:
> Douglas;
>
> I've never had one apart, so I don't know what the failure mode is. It could be seals or wear on a seat. You'd want to be very confident in your ability to rebuild a servo given that these cars are totally impossible to stop without power assist. If your rebuild failed in use, well, it wouldn't be pretty.... I imagine the parts would be hard to acquire given they don't expect these to be rebuilt. They don't even want the old one back as a core.
>
> Fred
>
> -----Original Message-----
> From: Douglas Fifield [mailto:douglas.fifield at gmail.com]
> Sent: July 3, 2006 9:33 AM
> To: Fred Munro
> Cc: brian hoeft; s-car-list at audifans.com
> Subject: Re: [s-cars] Brake Light and Thrumming Pedal
>
>
> Fred,
>
> What is it that fails in the servo?  Seals?  Must be rebuildable,
> wouldn't you think?
>
> D.
>
> On 7/3/06, Fred Munro <munrof at sympatico.ca> wrote:
> > Douglas;
> >
> > You need one foam gasket between the firewall and the servo. The Bentley shows an o-ring between the servo and the master cylinder that doesn't show up on ETKA and wasn't on my OEM servo when I removed it - probably been superceded and not used. You will need 4 new locknuts for the servo studs. I reused the old pin clip but it doesn't hurt to replace it. As a matter of interest, the new servo I bought from the dealer was manufactured in 1992 and had an expiry date on the box of October 2006.
> >
> > Fred
> >
> > -----Original Message-----
> > From: Douglas Fifield [mailto:douglas.fifield at gmail.com]
> > Sent: July 3, 2006 12:41 AM
> > To: Fred Munro
> > Cc: brian hoeft; s-car-list at audifans.com
> > Subject: Re: [s-cars] Brake Light and Thrumming Pedal
> >
> >
> > Bryan, Fred, All,
> >
> > Yes, it was the line on the very top of the servo that I disconnected
> > and replaced with the 8" brake line.  So it appears the servo is toast
> > and needs replacement.  Shit.  Well, it is better to know what is bad
> > and fix it than to not know at all.  Will seek replacement tomorrow.
> >
> > Now, further questions - looking at the FA and the Bentley, it appears
> > I need a replacement circlip for the pin, two gaskets (why 2), and 8
> > lock nuts (why 8 and not 4).  Is that the concensus?
> >
> > D.
> >
> > On 7/2/06, Fred Munro <munrof at sympatico.ca> wrote:
> > > Douglas;
> > >
> > > If it's the return port you connected to (the one on top of the servo) your servo is toast. There should be no fluid coming out of this port unless the brake pedal is depressed.
> > >
> > > Fred
> > >
> > > -----Original Message-----
> > > From: Douglas Fifield [mailto:douglas.fifield at gmail.com]
> > > Sent: July 2, 2006 5:30 PM
> > > To: brian hoeft
> > > Cc: Fred Munro; s-car-list at audifans.com
> > > Subject: Re: [s-cars] Brake Light and Thrumming Pedal
> > >
> > >
> > > All - followup.
> > >
> > > Got the fitting loose. Got the bending tool - used it.  Clamped return
> > > line on servo and swapped it for the 8" brake line mit tube into
> > > bottle.  Started engine and watched a solid, pulsing flow of fluid
> > > fill the tube and drain into the bottle.
> > >
> > > Please confirm that this means my servo is toast.  If so, I will try
> > > to source one tomorrow.
> > >
> > > D.
> > >
> > > On 7/2/06, brian hoeft <qweblog at gmail.com> wrote:
> > > >
> > > > i used a standard craftsman wrench..
> > > >
> > > > first make sure your turning it the proper way.. i know it sounds dumb but
> > > > it isnt.
> > > >
> > > > you can typically feel when its gonna give and strip but its likely itll
> > > > give and bust a knuckle just before that.  i made sure my hand was clear of
> > > > danger and went at it like i meant it.  dont recall if i used PBblaster, but
> > > > if youre worried you can wipe the excess before breaking it free..
> > > >
> > > > tis all for now, //brian
> > > >
> > > >
> > > > On 7/2/06, Douglas Fifield <douglas.fifield at gmail.com> wrote:
> > > > > OK, I'll check.  Here is my other question for the day.  How in blazes
> > > > > to you get the fitting on the return line off?  I can't find clearance
> > > > > for my 11 mm brake fitting wrench.  I can get a cheap 11 mm stubby on
> > > > > there, but it didn't want to budge and I am afraid of using too much
> > > > > force with that wrench and stripping the hex head on the fitting.
> > > > >
> > > > > I am leary of using penetrating oil in this application.
> > > > >
> > > > > Any suggestions?
> > > > >
> > > > > D.
> > > > >
> > > > > On 7/2/06, brian hoeft <qweblog at gmail.com> wrote:
> > > > > >
> > > > > > that same NAPA should sell a tube bender,the guys at the counter might
> > > > know
> > > > > > it better for bending brake lines.. looks kind of like a hockey stick
> > > > w/a
> > > > > > groove to hold the line in place.
> > > > > >
> > > > > > should be just a few bucks for the one you'll need.
> > > > > >
> > > > > > good luck, //brian
> > > > > >
> > > > > >
> > > > > >
> > > > > > On 7/1/06, Douglas Fifield <douglas.fifield at gmail.com> wrote:
> > > > > > > Fred,
> > > > > > >
> > > > > > > I just walked into the house from NAPA with an 8" section of metric
> > > > > > > line.  Sounds just like what you describe.  Do you have advice on how
> > > > > > > to bend it without kinking it?
> > > > > > >
> > > > > > > D.
> > > > > > >
> > > > > > > On 7/1/06, Fred Munro < munrof at sympatico.ca> wrote:
> > > > > > > > Douglas;
> > > > > > > >
> > > > > > > > Ask for 3/16" European metric brake line. It will have the proper
> > > > flare
> > > > > > and nut.
> > > > > > > >
> > > > > > > > I've attached a photo of my test apparatus.
> > > > > > > >
> > > > > > > > Fred
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > -----Original Message-----
> > > > > > > > From: Douglas Fifield [mailto: douglas.fifield at gmail.com]
> > > > > > > > Sent: July 1, 2006 12:16 PM
> > > > > > > > To: Fred Munro
> > > > > > > > Cc: s-car-list at audifans.com
> > > > > > > > Subject: Re: [s-cars] Brake Light and Thrumming Pedal
> > > > > > > >
> > > > > > > >
> > > > > > > > All,
> > > > > > > >
> > > > > > > > So, if I want to test the servo as described and go to the FLAPS to
> > > > > > > > get a piece of metric brake line, is there just one size of flanged
> > > > > > > > fitting, or do I need to know the correct size?  If the latter, can
> > > > > > > > someone supply that info?
> > > > > > > >
> > > > > > > > Douglas
> > > > > > > >
> > > > > > > > On 6/30/06, Fred Munro < munrof at sympatico.ca> wrote:
> > > > > > > > > Douglas;
> > > > > > > > >
> > > > > > > > > If the level doesn't fall, the bomb is not being charged with
> > > > fluid.
> > > > > > This could be a really bad servo or a bad pump. At this point I'd do the
> > > > > > servo test to rule that out. A totally dead bomb would also not draw
> > > > fluid
> > > > > > out of the reservoir, but it should allow the system to pressurize and
> > > > the
> > > > > > light would go out.
> > > > > > > > >
> > > > > > > > > I replaced the servo in a couple hours. You don't need to do a
> > > > brake
> > > > > > bleed - you remove the two bolts securing the master cylinder to the
> > > > servo,
> > > > > > release the brake lines to the MC from the multi-line clamp, and slide
> > > > the
> > > > > > MC off the servo without removing the brake lines. When the new servo is
> > > > > > installed, you slide the MC back onto the servo and bolt it up. You
> > > > don't
> > > > > > have to open up the lines or bleed the brakes.
> > > > > > > > >
> > > > > > > > > As Brian mentioned, the servo is secured by four 13mm nuts that
> > > > also
> > > > > > secure the pedal cluster. The top left nut is a bit tricky as Brian
> > > > points
> > > > > > out, but I got it using 18" of 1/4" drive extensions and a flex end. You
> > > > > > have to use 1/4" drive stuff or you can't see past the extensions to the
> > > > > > nut. You have to use multiple extensions and assemble them as you insert
> > > > > > them through the hole in the pedal cluster. Remember to get a new sponge
> > > > > > gasket to seal the servo to the firewall. Unfortunately I didn't do a
> > > > > > write-up on this.
> > > > > > > > >
> > > > > > > > > Hopefully you don't need a servo, but the alternative is probably
> > > > the
> > > > > > pump. If the servo tests good, you'll have to make up a pressure testing
> > > > rig
> > > > > > or take the car to the dealer to test the pump output pressure.
> > > > > > > > >
> > > > > > > > > HTH
> > > > > > > > >
> > > > > > > > > Fred
> > > > > > > > >
> > > > > > > > > -----Original Message-----
> > > > > > > > > From: Douglas Fifield [mailto:douglas.fifield at gmail.com ]
> > > > > > > > > Sent: June 30, 2006 11:07 AM
> > > > > > > > > To: Fred Munro
> > > > > > > > > Cc: s-car-list at audifans.com
> > > > > > > > > Subject: Re: [s-cars] Brake Light and Thrumming Pedal
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > 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
> > > > > > > > > > >
> > > > _______________________________________________
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> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > --
> > > > > > > > > > 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
> > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > --
> > > > > > > > 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
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> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > > > --
> > > > > 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
> > >
> > >
> >
> >
> > --
> > 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
>
>

-- 
Douglas in MN
95.5 Audi S//6 Avant
73 BMW R60/5 mit Toaster Tank