There is a proportioning valve on our VR4 mounted between the ABS unit and the rear brakes (Workshop Manual 35A-2, 35A-7 or pages 87 and 92 of the translation Vol.2). It’s wondering me, because the ABS unit should do the work. Or am I wrong?

I’m asking this because my car didn’t pass the Dutch MOT. There was a difference of more than 60% in brake operation between rear right and left. So I was thinking about a problem in the ABS unit. But there is no dash bulb warning. Looking closer under the bonnet I saw the proportioning valve.

So I have two questions:
- Why is there a proportioning valve
- What can be wrong with my rear brakes. I did a complete revision some years ago and pistons etc are 100% ok. Can it be the ABS unit or maybe the proportioning valve?

Thanks for your attention.