That isn't the one I'm referring to. On the inner fender well, there are the proportioning and metering valves (2 seperate brass blocks). A short (24 inch or so) line runs toward the rear of the car, to the block I mentioned on the inside of the frame rail. The long line comes off this bl;ock to the brass block mounted on the axle, which appears adjustable. I assumed the block mounted on the axle controlled the amount of pressure the rear brakes saw. As I understand it, my system was only offered on the early 70 model year cars. Later 70 cars combined the metering/proportioning valves into one, and eliminated the frame rail block in question. Can anyone verify any of this?