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Weird Hydraulics

> From: David Powell <dpowell@mdtech.is.ge.com> - who wrote:

> The first warning light I got on my dash was because of low rack oil in the
> reservoir.  I added rack oil.  The oil was pushed right out of the resrvoir
> cap within a very short time.  

Possibly(?)  normal fluid rise & fall when engine goes on and off.

>My brakes are fading like crazy sometimes.  Other times they
> feel fine.  I never really know what it will be like when I press the pedal.
> I've been doing a lot of two footed braking lately.  Once the brakes are 
> pumped up they seem to work well.  If I don't use them for a few minutes
> they get soft, then very manual.  The brake reservoir is full and never 
> needs fluid.  I recently bled the whole system just to see if it would help.
> The brakes have not been bled in the last 120k miles as far as I know so I
> figured it couldn't hurt.  The power steering is working reasonably.  

So far, sounds like it might be a pressure accumulator problem.

> I've
> got a friend that road trips with me who says the settering is getting
> worse but I don't notice since I drive the car every day.  It is by no
> means manual.  This leads me to believe the power steering pump (remanufactured
> ZF) is still working.  

If the pump failss, you lose power assist for brakes and steering.  
That's a fast clue.  However - if you feel pulsing thru the steering, 
it can (again) point at the pressure accmulator.

> The brakes seem very solid and don't go to the floor
> when the car is off.  

Really?  Have you tried counting pumps to see when assist drops off?  
(I'm not casting the first stone - I STILL can't feel any difference 
when the engine is off.  I have done this six times and just CANNOT 
feel any difference unless the car is moving...so I don't consider 
this much of a test unless the car is moving...)

> When the car is running I can force the pedal to the
> floor with the help of the servor.  I don't know if this is supposed to 
> happen.  I reason the brakes would fade with the car off if the master 
> cylinder was falty so I don't think it's the master cylinder.

I don't know what to think of this.  It does not sound right to me, 
as I can't press the pedal to the floor at ANY time, running or not.

> My bentley manuals suggested I remove reservoir return hose from the brake
> servo and see if fluid comes out.  None did.  I put everything back together
> and pumped up the brakes, then shutdown the car and repeated the test.  Fluid
> oozed out slowly.  This may indicate a leakly servo but I don't know if it
> is my major problem.  On a car this old there may be several things going
> on.  

Sounds to me like your brake servo is OK.  That test is supposed to 
be definitive.

> I'm not interested in completely reconditioning the brake system.  I
> want to fix the one thing that is causing my power brakes to die completly.
> My bently manual suggests I do a few other tests with a pressure guage.  I
> don't have one.  I don't want one unless it's cheap.  I'll take it to a 
> shop if it comes to that.  What I'm hoping for here is some educated and
> experienced guesses about which parts may be failing.  I have a feeling
> the shop will test my car and tell me they are all shot, replace the works,
> or better yet junk the car.  

An Audi tech can stick a pressure gauge in that system and check the
pressure in less than one hour; it's well worth the labor charge.  At 
this point, my guess is:  TA DA! - The pressure accumulator.

You DO have the idea that bleeding the brake system is a totally 
separate fluid than the steering/brake servos, right?  Remember that 
those two systems are separate and use different fluids.  I see from 
the notation at the end of your post that you understand this...

Keep us posted. 

********** A Washington State Cougar in Aggieland (aTm) **********

Al Powell                           Voice:  409/845-2807
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