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

[brian bilotti]

Fred,

Thank you for the rundown. The manifold pressure has
been thought of and a check valve seems to be a "fix"
for that issue. I really do appreciate all the sound
advice. I just want this thing fixed...

I'll let you know how it goes.

Brian
--- 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
> 
> 
>      
>
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