Faulty Proportioning Valve ?

Greville Bowles zaphod at cansafe.com
Fri Nov 12 16:50:08 EST 2004

Well, we have started to narrow down the possibilities re: the rear rotor
corrosion problem on my '95 90Q. First some background:

New rotors & pads all round - Fall 2002

Replaced rear wheel bearings - Summer 2003. There was no apparent brake
problem at that time.

Oct. 2004 - replaced very noisy right rear wheel bearing. Left side is ok.
During that work it was apparent that there was a problem with the rear
brakes, in that the rotors we very corroded and making minimal contact with
the pads.

Last weekend - Replaced rear rotors, cleaned and inspected calipers,
replaced rubber booties. Observations:  Pads only lightly worn. While
tightening the wheel bolts the real wheels could be turned by hand with the
brakes applied (read: 0 stopping ability) The hand brake functioned fully,
solidly locking the wheels. The front brakes are working well.

So, I'm thinking it's time to look at the hydraulics, and my first guess is
a faulty proportioning valve. Bentley tells me to use the VW1310 tool (a
pair of hydraulic gauges on a stand) to simultaneously measure the pressure
at the left front & left rear bleeder valve. If the pressure is outside the
given range, replace the proportioning valve. Since I don't have the VW1310
tool, this sounds like a dealer visit.

Before I go to the dealer, is there anything else I should look at that will
help to diagnose the problem? Any BTDT's?

The following is more background just in case there is some relationship
that I'm not seeing. It may mean something to others.

Once I get the brake issue(s) resolved I'll need to find out why that rear
bearing went so quickly (24,000 miles). The noise started during a trip to
NC. I had the alignment done down there and the mechanic said that the rear
wheels were way out of alignment. Alignment was done less that 1 year prior
and I've had no "incidents" since then. I assume that was the cause of the
odd wear pattern on my new tires (1-2 inch wide bald strip on the inside
edge of the rear tires).

Another item I need to look at is amount of play in the drive train to the
rear wheels. I can turn the wheels 3 to 4 inches with little or no
resistance. Is this normal? Perhaps the CV joints are worn? Or the

The clutch release bearing is getting rather loud. I suspect that will need
attention soon. What all should be done "while we're in there"?

Every time I do something on this car I'm into the great unknown. If not for
the helpful folks on this list and my good buddy George, I'd be spending a
fortune at the dealer (or driving a Kia). Thank you 1 and all for keeping my
sorry ass out of a Korean tin can.

I just called the dealer.

Clutch job (disk, pressure plate & bearing) = $1100 + tax
Proportioning valve $200 + $126 labor + tax

Mr. Greville H. Bowles
RR 5, Rockwood, Ontario N0B 2K0
E-mail:   zaphod at cansafe.com
'95 90Q
'85 245
'83 GS650GL

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