[s-cars] Master cylinder help

Mon Jul 25 20:25:36 PDT 2011

Serge;

Is the red "brake" light on indicating low pressure in the brake boost
circuit? If not, is the low pressure switch on the servo working and
connected? If you are feeling pump pulsation through the brake pedal it
usually means the accumulator (bomb) is not storing pressure and the low
pressure warning light should be coming on. You can test the light by
turning the ignition to "ON" with the engine OFF and pumping the brakes
until the pedal goes hard (should be 20+ pumps on a good bomb). The red
"Brake" light should come on when the pedal is hard (bomb is discharged).
Leave the handbrake OFF when doing this test - the handbrake also turns on
the warning light.
If you have a low pressure problem the culprit is usually a bad servo, a bad
check valve in the bomb, or a bad bomb. It sounds like you've tried several
bombs, so the bomb and check valve is not likely the problem. Have you
tested the servo for leakage? If you've had a hose fail, the rubber bits can
travel throughout the system and cause problems. Some of the banjo bolts
have small screens inside the bolts that can get plugged and restrict fluid
flow. These cars are impossible to stop if the brake boost system fails, so
it is important to keep the boost system and the warning light in good
working condition.

Good luck!

Fred Munro
'97 S6

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com] On Behalf Of serge
Sent: July 25, 2011 6:55 PM
To: Tom Green; s-car list
Subject: Re: [s-cars] Master cylinder help

Ok, in re-reading my post I see Tom¹s point, and a couple of you emailed
with comments about rotors... So let me try to add some
details/clarification.

While driving the car, brake pedal pulsates when brakes are applied. It is a
pulsation, not a vibration. The pulsation is not felt through the steering
wheel. Additionally, the pulsation is not a vibration, as associated have
with an out-of-round or out-of-balance wheel/rotor/tire type situation. It
is as though you can feel the hydraulic pump pumping, when you depress the
pedal. Its been q while now, and I¹m not 100%on this, but I don¹t believe
the pulsation was there if the car was stationary, so no pulse if the car is
idling, and the brake pedal is applied...

Thanks for all the help so far, keep the suggestions coming.

-Serge

On 7/25/11 5:10 PM, "Tom Green" <trgreen at comcast.net> wrote:

> I don't believe I would start with the brake master cylinder, especially
if I
> wanted to
> conserve resources.
> 
> One immediate problem is that this lengthy post has provided very little
hard
> information about the problem.  You have some definite idea just what this
> pulsating brake pedal problem is, but you have provided the list with very
> little
> solid information.
> 
> Does the brake pedal pulse only when the pedal is depressed?  Does the
vehicle
> have to be in motion and the pedal pulses while it is braking to a stop?
Or,
> does
> the pedal pulse when the car is stopped?  But the engine must be running?
> When 
> the vehicle is in motion and is being braked to a stop, do the braking
action
> on the 
> car pulse as well, or is it just felt in the pedal?  Does the passenger
feel
> the braking 
> action pulsing also?
> 
> I am not certain by any means that such answers will help solve the
problem,
> but 
> it is a start if it includes any other abnormal operation of the brakes.
> 
> There are several individuals parting UrS vehicles and announcing it on
the
> UrS cars forum on Quattroworld.com.  That should be a source for
inexpensive
> parts.  
> 
> Tom '95 S6  
>          '95.5 S6 avant
> Knoxville, TN
> 
> 
> On Monday July 25, 2011, at 1:16 PM,  Serge Filanovsky
<s6serge at verizon.net>
> wrote:
> 
>> Hi everybody, its been a long time since my last post. My S6 avant came
to
>> an abrupt demise via a Japanese sh!tbox-- the cell-phone-clutching,
upstate
>> New York lady came down to the big city to blow through a red light and
take
>> out my driver's side front (enough for the Gecko to say its a total
loss). I
>> had a car full of people, an no one was hurt. These cars are truly tanks.
>> 
>> But this is a tale of hope and resurrection. The car sat at my mechanic's
>> for less than a week, and a young lad from the neighborhood decided he
>> wanted to fix it up. I had a few parts need for the fix (along with all
RS2
>> bits) Rossato-Binned in my basement, so a deal was struck. A few months,
2
>> new headlights, and a whole lot of elbow grease later, the car was back
on
>> the road! Looked damn good too!
>> 
>> But trouble was brewing in the braking department. A pulsating pedal that
>> neither I or my mechanic could track down (tried new bomb or 5, new pump,
>> new hose, flushed the system 5 times... pulsation is still there, worse
>> during summer months--high humidity--less so in winter, has been the only
>> clue) had gotten so bad, that the car is now parked (also coincided with
the
>> failure of power steering hose, which has been sent to Spokane House of
>> Hose), and the fluid reservoir caming off the master cylinder, spilling
all
>> the brake fluid...I'm surprised lightning didn't hit it twice just then.
>> 
>> So my young friend is desperately trying to get the car back together in
>> time for his FIRST S//Fest attendance. But brake system frustrations, and
>> lack of sleep (and funds) due to a brand new baby, have him seeking
>> desperate measures. He's considering converting to vacuum assist for the
>> brakes ala non-turbo 100. Not being a big fan of vacuum assist on turbo
cars
>> (I know its been done), I'm trying to convince him to try a new
(different)
>> master cylinder first.
>> 
>> That's where you guys come in. I'm looking for:
>> 1) any thoughts on brake-pulsating problem
>> 2) anyone who has a good-known master cylinder in their Rossato-Bin, or
>> knowledge of where one can be sourced cheaply (dealer price is something
>> like $600 + the new baby)...
>> 
>> As always-- TIA,
>> 
>> -Serge
>> 
>> '03 S8
> 
> 
>  
> 
> 

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