[urq] Brake pressure regulation on urQ

[Louis-Alain RICHARD]

Hi there,

The last thread about brake bleeding pushed me to read carefully the IST to
understand how the brake proportioning valve (BPV) is working. Just for the
fun of it. Yeah, I don't have a social live, I know...

Now I am confused.

1-	Standard FWD BPV are often bolted to the rear axle and reacts to the
movement of the rear suspension to adjust rear brake pressure. Nice, easy to
understand. Dynamic brake pressure regulation.
2-	A manual BPV will be set by an operator, according to different road
conditions. Also easy to understand.
3-	The newer cars have Electronic Brake Pressure regulation: it's a
spinoff of the ABS/EDL circuitry that releases brake pressure when a wheel
slows at a faster rate than the others, before the ABS kicks in. Also
dynamic brake pressure regulation.

Now, on our urQ, there is this "pressure-dependent" BPV, according to IST.

>From what I read (the pictures are too dark to really understand the
internals), it regulates the rear pressure in a fixed ratio of the front's,
right? There is also a safety bypass in case one of the circuits is leaking,
so there is always at least some braking after a failure.

So this device is not dynamic at all, it cannot adjusts for difference in
weight repartition or anything else. No matter what, there is always X
percent of the brake pressure going to the rear wheels.

Now, how can I improve this repartition other than changing only rear brake
pads or front tires? You know, my car is prone to front wheel lockup and no
matter what I do (except flooring the brake pedal), rears won't lock.

But then, if I install "aggressive" rear pads, and the rear wheels are
locking too soon, I still have a problem...
Brake system is mostly rebuilt/new, and the rear calipers are working.

Suggestions are welcome, as usual.

Louis-Alain
83 urQ with stock braking system