proportional valve: how important to have working one?

[Dupree, Jim]

Well according to Bentley (I don't have a type 44) the 100/200 quattro's
have a rear brake pressure regulator. Section 47, page 5 give the adjusting
and testing procedure for it. Section 47, page 3 (I think) is the adjustment
and testing for the front wheel drive 100/200's. It operates via a spring
and lever to/from the right rear control arm. There is also a brake pressure
limiting valve on the left rear control arm. I am pretty sure this is the
same on the 5000 quattro's as well but I don't have the book here to look
at. The 4000 quattro's and the 80/90 quattro's only have a fixed rate
pressure regulator.

Thanks
Jim

 -----Original Message-----
From: 	Huw Powell [mailto:human747 at attbi.com]
Sent:	Tuesday, February 26, 2002 4:16 PM
To:	quattro at audifans.com
Subject:	Re: proportional valve: how important to have working one?



> I didn't know that quattros got the active proportioning valve
> thingies. Wouldn't the 89's have ABS anyway? So wouldn't we be taking
> about the proportioning valve situated under the master cylinder? The
> one you're not supposed to be adjusting anyway? Or am I just confused?

yes... on the 2wd cars, the valve is down by the rear axle and
presumably alters it's effect slightly depending on how much "pull"
there is on a spring going to it.

On quattros, which don't have a dual diagonal braking system, the prop
valve is under the master and is set to a fixed ratio.

The main function is to "proportion" the front and rear braking
pressure, I guess the rears do not require as much since there is less
weight back there, especially when the car noses down during braking.
Some people bypass them when they go bad - I would worry about the rears
locking up in a hard stop, perhaps making control of the car less
predictable.

As I recall from some long ago reading, the brake fluid pressures are
measurable different front to rear - I think the rears were about 75% of
the fronts.

> >>Proportional valves on both my cars do not work.  They are frozen.  How
> >>significantly it affects braking?  Can it freeze in such position that
> >>reduce overall braking power?


--
Huw Powell

http://www.humanspeakers.com/audi/

http://www.humanthoughts.org/