Problem with brakes, need some help.

[Fred Munro]

Hi Konstantin;

Sounds like your proportioning valve is shutting off the fluid flow to the
rear brakes.

Fred

-----Original Message-----
From: quattro-admin at audifans.com [mailto:quattro-admin at audifans.com]On
Behalf Of Konstantin Bogach
Sent: March 9, 2003 9:03 PM
To: Fred Munro
Cc: quattro at audifans.com
Subject: Re: Problem with brakes, need some help.


Hi Fred.  Thank you for such comprehensive post.
I bled MC - no air, and it is new (2 years, total about 8 month driving).
Bled
wheels again - no air detected.
The only strange thing I noticed:  when I cracked opend bleeder valve on
both
rears, fluid does not came out as it should be, just 1/4'' appears in the
tube
and that is it.  When I touched proportioning valve arm, fluid started to
flow
normally.  I don't know whether it was an accidental coincidence or not.  I
removed the valve, did not disassemble it yet.  I am done for today.  I will
post my finding.

Thank you.
Konstantin.

Fred Munro wrote:

> 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