Re: Rear proportioning valve prollems

[Don Hoefer <hoefer@eng.pko.dec.com>]

Audi's namesake, August wonders:

> With the car (88 5kCD TQ) completely suspended in the air by its frame
> & no form of a drivetrain, the left rear wheel is binding enough that
> I was able to tighten the wheel bolts for my new Sport wheels without
> holding the tire.  I'm _guessing_ this has to do with the rear
> proportioning valve that controls that wheel.  Yes, the whole car is
> off the ground, however, that proportioning thingy is a solid ball of
> rust.  The lever that is supposed to move can't be budged with a
> hammer, so it's completely useless.  So, the question becomes:
> 
> 1)  How important is it?  I very regularly toss 3 or 4 people (kicking
> and screaming usually) into the car, plus a bunch of luggage etc for a
> long weekend of camping or skiing or whatever, but also use it to
> commute 100 miles a day in, so the rear weight is constantly varrying
> rather considerably.

I'm not an expert, but it is very important.  More so in the FWD cars
than the quattros.  It keeps the rear brakes from locking the wheels,
a very bad thing to happen.  I think that when they go bad, they do
nothing.  Which is preferable to applying the rear brakes full on
which would happen if the brake lines were directly connected.  Back
in the early '80's when everyone was coming out with FWD cars there
were several recalls (none for Audi, they got this right) for cars
that had fixed ratio brake proportioning valves.  If there was not
enough load on the rear wheels, the wheels would lock under braking.
Even when the car is fully loaded, the rear brakes only get a fraction
of the brake fluid pressure that the front brakes receive.

> 2)  How bad would it be to toss the thing in the trash and just couple
> the two brake lines together?

If you can't replace it with a known good one, do nothing.

Could your wheel be binding due to your e-brake cable being too taught when
the car is lifted?

Don Hoefer
'82 Coupe

Massachusetts, USA