I just completed a rear disc brake conversion on my 76 FJ-40 (using the Monte Carlo clipers). Like many of you, I'm experiencing premature rear brake lock-up. It's beautiful under normal braking, but if I had to stop under a real emergency, I'm sure the rear would lock up. Right now.....I'm using the stock Toyota proportioning valve. Obviously, I want safer brakes if I can get them. I have spent hours on the "search" feature, and conclude that adding an adjustable proportioning valve might/might not solve my problem. So here is my question...... Has anyone taken the stock Toyota proportioning valve apart to see if it can be shimmed (or probably shims taken out) to decrease pressure to the rear brakes? Any advice here?