[s-cars] Brake servo help

[Tate Pinto]

>Doug,
It used to come on under heavy braking until I replaced the bomb. You
know it's the bomb if after waiting for the light to go out you turn
off the engine and pump the brakes until the pedal gets hard. I think
the guideline for replacement is 10-15 pumps while a good bomb will
go 25+ pumps. While diagnosing Scott Mockery (www.SJMAutotechnik.com)
helped me out with this explaination of what is going on with the
brake servo.

Scott Writes:
If the brake servo was leaking in your car, it would seem that when
the car sits overnight, the bomb would discharge its stored up
pressure through the servo leakage path and push fluid into the
reservoir through the return line. The Bentley test that has you
remove the return line from the servo and check for excessive leakage
would help confirm this.
When you first push on the brake pedal the next morning before start
up, the pedal would likely be hard if the servo had been leaking and
all the stored pressure was  lost in the bomb. After startup the
pedal would sink down as the assist comes up as the system pressure
rises and as the bomb is getting filled charged up with pressure. The
bomb would test ok with the engine off, when pumping the pedal many
times, now that the system has charged up the bomb again.
This sounds like what was happening in your case from what you
described at startup. I have not actually seen many of the servos
fail on the 5kTQ, 200TQ, or on the S4/S6's, but yours could be leaking
>

I have the above symptoms and when I detached the return line per the
above procedure it created a nice little puddle in my driveway
(luckily I rent) so I'm pretty sure it's the servo at this point.
>
>---- Original Message ----
>From: landaeta1 at comcast.net
>To: tate at kioskousa.com, s-car-list at audifans.com
>Subject: RE: [s-cars] Brake servo help
>Date: Wed, 21 May 2003 09:41:24 -0400
>
>>No actual help here, but in your diagnosis, did the brake light come
>on
>>under hard braking? I just figured my prob was the bomb, and want to
>>understand the diagnosis procedure of bomb vs. servo.
>>
>>Doug Landaeta
>>94 S4
>>
>>
>>-----Original Message-----
>>From: s-car-list-admin at audifans.com
>>[mailto:s-car-list-admin at audifans.com]On Behalf Of Tate Pinto
>>Sent: Wednesday, May 21, 2003 9:16 AM
>>To: s-car-list at audifans.com
>>Subject: [s-cars] Brake servo help
>>
>>
>>
>>I was looking for a little of this groups expertise. After replacing
>>the bomb and checking the pump to bomb hose I've determined that my
>>brake servo is the culprit behind the brake light staying on for
>>10-20 seconds at startup. I went ahead and bought a used servo in
>>good condition from Scott Mockry - all is good until I stick my head
>>in under the dash and can't see the upper left-hand corner bolt that
>>attaches the servo to the firewall. Is there an easier way to get to
>>this rather than pulling apart the pedal assembly? I looked in the
>>Bentley manual but did not see directions for this procedure.
>>
>>Any help is appreciated
>>
>>-Tate Pinto
>>94 S4 / Newton, MA
>>
>>
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>>