[s-cars] Brake/Power steering system drama-

Fred Munro munrof at sympatico.ca
Tue Nov 20 19:24:13 PST 2007 

Brian;

I think any of the banjo bolts can contain screens. I've seen them in the
bolts on the pump.

The top line on the servo is the return line to the reservoir. When the
brake pedal is depressed, fluid flows through the servo and back to the
reservoir through this line. If the servo is OK, you can remove the line and
only a few drops of fluid should leak out (with the brake pedal NOT
depressed and the system pressurized). If the servo is shot, fluid will flow
through this port even if the brake pedal isn't depressed. This is one way
the bomb can lose pressure once the engine is shut off.

If you want to purge the servo using the top port, a standard metric brake
line and fitting will thread into the port. You can attach a plastic hose to
the brake line and lead it into a bottle. Pumping the brakes with the engine
running will transfer fluid from the reservoir into the bottle. Actually,
this is how I test the servo - if fluid flows through the line with the
engine running and the brake pedal not depressed, the servo is shot. You may
want to test the servo if you've had ATF in the system.

HTH

Fred
  -----Original Message-----
  From: brian hoeft [mailto:qweblog at gmail.com]
  Sent: November 20, 2007 12:43 PM
  To: Fred Munro
  Cc: brian bilotti; s-car-list at audifans.com
  Subject: Re: [s-cars] Brake/Power steering system drama-


  Fred, when you suggest removing the banjo bolts to purge the
system/screens with the car off are you referring to 2 on the rack itself or
all, like the one at the bomb too?

  Also, If the 12 o clock line on the servo were removed (after pumping to
depressurize) before starting the car, wouldnt the system purge itself that
way as well, so long as the reservoir still pulled in new fluid?

  ..Im having to replace my pump in the near future from my cross country
line failure & ATF emergency fluid use and want to get all the red stuff out
as best as possible..

  Thanks, brian



  On 11/19/07, Fred Munro <munrof at sympatico.ca> wrote:
    Brian;

    The steering and brake systems are independent to a certain extent but
they
    use a common fluid reservoir and pump. The pump has two circuits; a high
    pressure low volume section for the brake assist and a low pressure high
    volume section for the steering.

    The light on and the hard brake pedal indicates you have low pressure in
the
    brake boost circuit and therefore little or no brake assist. The car is
    dangerous to drive in this condition as it cannot be stopped easily
without
    brake assist (as I'm sure you've found out).

    The system as installed is quite reliable when operating properly. It
would
    be much easier to sort out the hydraulic boost system than to cobble
    together something else. Some of the older non-turbo cars (coupes,
4000's,
    100) that you mention in your post use a vacuum brake boost system that
    takes it's vacuum from the intake manifold. That would work fine until
the
    turbo kicked in and pressurized the manifold, hence the hydraulic system
on
    the turbo cars.

    First of all, your "bomb" (hydraulic accumulator) is not holding
pressure.
    With the engine off, fluid is leaking out of the bomb and back into the
    reservoir. You can confirm this by looking at the reservoir level with
the
    engine running and the light out and checking the level again after the
car
    sits overnight. If the level rises overnight, the bomb is leaking back
into
    the reservoir. This can be caused by a bad check valve in the bomb or a
    leaking servo.

    When you start up the car and get the light and a hard brake pedal, that
    tells you that there is no stored pressure in the bomb to boost the
brakes.
    The fact that the light stays on for a long time and the pedal stays
hard
    tells me that the pump isn't pressurizing the circuit enough to boost
the
    brakes. Usually with a dead bomb and good servo the pump will build
enough
    pressure to give you easy braking for an "average" stop but not enough
for a
    panic stop. When you stop and give the pedal some "serious pushing" you
are
    pulsing the servo. Since this resolves the problem I suspect you have a
    servo issue, probably hose debris clogging the internals. The servo is
    probably leaking by so much that the pump can't pressurize the circuit.
    After you pulse it, it stops leaking by and allows pressure to build in
the
    boost circuit. You can check this by doing a leak-by test on the servo.

    I'd start by draining the hydraulic fluid, pulling all the banjo bolts
to
    clean the internal screens, and pulling and cleaning the screen in the
    reservoir. Turn the wheels side to side (with the engine OFF) to force
the
    old oil out of the rack. Remove the reservoir and clean it out. Refill
with
    new oil and try it again. If this doesn't work and the servo fails the
    leak-by test, you'll need a new servo. No problem, they only cost $800
    *cough, cough*

    HTH

    Fred Munro
    '97 S6 (mit new servo)

    -----Original Message-----
    From: s-car-list-bounces at audifans.com
    [mailto:s-car-list-bounces at audifans.com ]On Behalf Of brian bilotti
    Sent: November 19, 2007 12:45 AM
    To: s-car-list at audifans.com
    Subject: [s-cars] Brake/Power steering system drama-


    S-Heads,
    If you'll recall, awhile back I had the J hose blow.
    Got it fixed at Pirtek, fast forward it blew again.
    They fixed it.
    Now on start up and for quite awhile the brake light
    stays on and the brake pedal is extremely hard to
    press. I end up pulling over and give the pedal some
    serious pushing to force it down. Drive a little bit,
    light goes off and everything's fine.
    I'm really sick of this BS.....

    Two questions:

    1. Any ideas WTF this is?

    2. Anybody change their brake system so the two
    systems are independant of each other?

    Javad has done it for the coupes and 4000 I think, but
    he can't do it for the Urs. Another buddy of mine says
    that a brake booster off a 100 and some other Audi
    parts (my mind is blank on that one, maybe a master
    cylinder) he seems to think this is a viable
    project.... That said, I wanna ask if there's been any
    BTDT out there.

    Lemme know

    Brian


         ___________________________________________________________________
___
    ______________
    Be a better sports nut!  Let your teams follow you
    with Yahoo Mobile. Try it now.
    http://mobile.yahoo.com/sports;_ylt=At9_qDKvtAbMuh1G1SQtBI7ntAcJ
    _______________________________________________
    S-CAR-List mailing list
    S-CAR-List at audifans.com
    http://www.audifans.com/mailman/listinfo/s-car-list
    _______________________________________________
    S-CAR-List mailing list
    S-CAR-List at audifans.com
    http://www.audifans.com/mailman/listinfo/s-car-list




  --
  ====
  ! beat the NWO cult ! www.RonPaul2008.com |  www.BWAnetwork.com/home
  www.humanhealth.wholefoodfarmacy.com | and be proud of my allies at
  >> www.hourofthetime.com

  //brian

More information about the S-CAR-List mailing list