I think you mean proportioning valve. (?) It sends the right pressure to each wheel and if it even can be adjusted I couldn't find out how. Shouldn't need adjusting. http://www.2carpros.com/makes/ford/bantam ..those guys discuss the Bantam, you might find what you are looking for there. I found Types, Function, Benefits, (cars with ABS don't have them.. the wheel speed sensors perform that function the proportioning valves do electronically) but nowhere and adjustment. As long as you have bled the brakes properly after replacing it you should be fine...and i do not take questions about brakes any way but seriously.
If you have too much bias to the rear, the tires will lock up during heavy braking. If you are hearing the rear tires locking up, reduce the pressure to the rear wheels.