If you limit the rear brakes with a prop valve, it would force you to apply more pedal pressure to make the rear brakes lock up. By limiting only the rear brakes, the fronts will "seem" like they work better only because you are pressing harder on the pedal without the rears locking up.
I may have missed it earlier in the thread, but do you have disc or drum brakes in the rear? If you have disc brakes and the MC wasn't spec'd for a disc rear truck that is likely a contributor to your problem.
I may have missed it earlier in the thread, but do you have disc or drum brakes in the rear? If you have disc brakes and the MC wasn't spec'd for a disc rear truck that is likely a contributor to your problem.