proportional valve: how important to have working one?

[Huw Powell]

> 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/