Problem with brakes, need some help.

[Fred Munro]

Konstantin;

Sounds like you have a few problems here.

The dead bomb could cause the rear brake problem because without the boost
provided by the bomb, you may not be generating enough pressure to activate
the rear brakes, particularly if the proportioning valve is stuck shut. Audi
Type 44s are heavily biased to front braking. In any case, you should not be
tooling around in the car with a dead bomb - you cannot panic stop without
the bomb because your leg is not strong enough to generate the hydraulic
pressure required without the boost provided by the bomb. The pulsating in
the pedal is caused by the dead bomb - the pulsating is the pressure pulses
from the hydraulic pump activating the brake boost servo.

The soft pedal is not caused by the bomb - a dead bomb results in a hard
high pedal. The soft pedal is air in the system or a bad master cylinder.
Even with a pressure bleeder, these systems can be hard to bleed.  Bleed the
MC first and separately. Then prop the proportioning valve wide open and
bleed the RR & LR calipers. Pulsing the system by opening and closing the
bleeder screw can shake trapped air loose. Tapping on the caliper can
dislodge bubbles trapped in the caliper.
Follow with the RF and LF calipers and try the brakes again.

If the problem persists, you may have to bleed the proportioning valve
separately, especially if the brake system was emptied of fluid when you did
the brake work.

The ABS issue may be caused by a wheel sensor dislodged when you did the
brakes.

HTH

Fred Munro
'94 S4


-----Original Message-----
From: quattro-admin at audifans.com [mailto:quattro-admin at audifans.com]On
Behalf Of Konstantin Bogach
Sent: March 8, 2003 3:06 PM
To: quattro at audifans.com
Subject: Problem with brakes, need some help.


Hi listers.

I finished complete brake system overhaul, bleeded but brakes are soft
and car is reluctant to stop. Bomb  is  dead.
With engine running pedal is pulsating as it goes down.  Bad bomb causes
it, according to some posts in archives.
After hard braking rear disks are dead cold.  I aslo want to mention
that ABS off light stays on when I try to switch it off (relay clicks).
But I believe it has nothing to do with soft brakes but ... just in
case.

My question is: can just bad bomb cause mentioned symptoms?

My second 200tq had also bad bomb before I changed it but brakes were ok
- not soft, no pulsation and brakes engaged ok.  This fact causes some
confusion in my head.

Thank you.
Konstantin Bogach.
200tq '89
200tqa '89
urS4 '93