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

[brian hoeft]

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
>
>
>
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//brian