I've got the proportioning valve ( Speedway.. on the rear brake line ) wide open. My goal is to be able to lock the rears up at 30 mph and then I can start closing the proportioning valve down until they barely squeal.
I picked up on your statement above and I want to make sure I understand it correctly, I was struggling with my rear brakes and the proportioning valve until I discovered that the adjusting knob should be turned the opposite of what I thought. It should be screwed in (clockwise) all the way to give you maximum pressure to the rear lines and brakes. It should be backed out all the way open to REDUCE the rear brake pressure. You stated that you have the valve "wide open". If it is the same type of valve I have then this would give you minimal brakes in the rear. We talked about this at this link too with a picture of the valve I have: