I'm in the process of upgradng to Disc brakes on the rear of my 1972 (Built 6/72) 240z. When trying to bleed the system, I have the pedal go down about half way and seems to hit something . Also not very much fluid flows out the caliper bleeders. I do get some fluid from both sides and did bleed the master. The calipers DO NOT move the pads!! NO REAR BRAKES! The pedal will NOT go the floor when I open the bleeder on a caliper or on the master for the rear section. I have an aftermarket Master cylinder installed at this time. I just bought a rebuild kit a master cylinder and will install it on my old original master. I noticed the "ORIGINAL HAS TWO "STOP SCREWS" but the new has only ONE STOP SCREW. Is this telling me anything. With the master removed the pedal moves all the way to the floor without any resistance. So I don't have any mechanical problem. ANY ideas of what to checkout?? I'm pretty mechanical (retired Mechanical Engineer and longtime backyard mechanic) Thanks, LOU