OK, I have a mini air guage by the air tanks.
I put another guage on the air line that attaches to the brake.
Both read the same pressure when I apply the brakes hard.
About 2/3 up the guage eguals 110-120 lbs.
The proportional feature workd too, can vary the pressure as I apply the brakes.
Must be the oring against aluminum coefficient of friction is poor.
I was thinking of putting disk of plywood? or something in the rim to improve the friction.
What would work for that?