Navy, Don't ever think that there cannot be a problem from the manufacturer here. I built a '65 mustang and added discs and purchased the master cylinder from Master Power brakes, a good ol' american company, the whole "direct fit" unit didn't fit I could tell before monting, I called and read them the part numbers off the instuctions and box (none on the unit itself) and they said its right and something is wrong with my mustang the parts are right and it might take a few extra mounting holes, I drill 'em bolt the thing up and nothing works I call 'em and they insist its right, I look up the pics on the net and call them and let them know they sent a 1968 unit in a 1965 box to me!! Now I have extra drilled holes in a smoothed firewall. Sometimes I think this stuff only happens to me, but reading this forum I can see I am not the only lone wolf out there! Point being make sure the MC is working you might have a seal on the MC piston with a wrinkle in it or something else only giving fluid to the front, like Roger mentioned a gauge would let you know, or take a rear caliper off and swap with the front with a socket in between to simulate the rotor and see if they are working hooked up opposite if you don't want to purchase a gauge. It appears you are dealing with a frame mounted MC and booster. You would not be able to notice the adjustement on a proportioning valve without driving it and cramming on the brakes, it merely limits pressure until the setting adjusted is overcome. I am sure we can keep coming up with something!