My '90 d250 has a bad rear propotioning valve. I can't find a new or rebuilt part! I've called everywhere and they (yes, even the dealerships) say that it's discontinued. What can I do? My rear brakes lock up/ get too much power..
There has to be some way to get an equivalent part, or fox this some other way, but I'm at a loss...

 

Google (adjustable proportioning valves) and take your pick.

 

autozone, advance auto, napa should have something in stock for you for around $20 get a universal adjusting valve.