[s-cars] Master cylinder help

[Peter Schulz]

Serge:

I had similar issues with the Mrs' rare' green/ecru Avant.
Also replaced the bomb x2, servo and eventually the pump, cleaned the reservoir filter a number of times (filter was pretty dirty) drained and replaced pentosin numerous times.

In this case the issue was extended time needed on startup to pressurize the system and rapid loss of residual pressure when the engine was turned off.

During the diagnosis and parts replacement process it also went through a period of pulsing when the brake pedal was applied with the car stationary.

Replacing the servo got rid of the pulsing, however did not remedy the extended time it took to charge the system.

I didn't have a pressure gauge, but did have a spare pump, so I swapped it out anyway.

(That) problem solved.

-Peter



On Jul 25, 2011, at 6:54 PM, serge wrote:

> Ok, in re-reading my post I see Tom’s 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 I’m not 100%on this, but I don’t 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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-Peter Schulz
Chelmsford Ma, USA
http://www.naaclub.org/

1995.5 S6 Avant Emerald/Ecru
1995.5 S6 Avant Silver/Platinum
1991 90Q 20v Q Red
1991 90Q 20v Indigo
1991 CQ silver  (eS2 recipient)