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'89 200TQ: urgent help with brakes needed.

Hello, virtual club!

In the light of a coming winter trip to Canada I fidally decided to adress an
old problem with rear brakes:

I have a feeling that my RR caliper(s) are binding after: 
a) a spirited drive with a few energetic stops or 
b) when I travel at normal speeds with aplying brake pressure rather gently,
but only with 4 people in the car. 
The car would not roll if I release the brakes on a light grade. Also the
first 20-30mm of pedal travel become virtually resistance-free and I hear a
faint hissing sound as the pedal goes through those 30-40mm. All goes away
after half an hour of standing still.

I suspect proportioning valve, since it biases brake pressure forward (around
80%-20%) on an empty car or splits it up evenly (around 50%-50%) on a loaded

How can one test a proportioning valve?

It might also very well be one or both calipers.

At the Glen this summer the car wore out LT RR pads at about twice the speed
of the RT RR pads. Now, this sounds like a LT RR caliper is binding. However,
yesterday the RT RR wheel was warmer and smelled like burning the friction
material, but a LT RR wheel did not.  A mystery. 
I have replaced the seals in both RR calipers this summer. The piston in the
LT RR caliper did travel in the bore with a slightly higher resistance, than
did the RT RR piston. I have also installed SS braided, teflon lined brake
hoses (from GPR), so no clogging of the old rubber hoses is expected.
I bleed the brakes religiously and I always use a pressure bleeder. The fluid
is Pentosin and I do not expect any air in the sys to be found.

So, before I bite the bullet and buy two new calipers, I would like to rule
out the proportioning valve.

Have anyone been there?

Thx in advance.

Igor Kessel