Son and I purchased a Series III, 88 inch, with bad brakes. It has 10 inch drums all around. Pedal goes almost to floor, but when pumped up, will stay up until you release it, then pedal next time will go to the floor again. Master Cylinder has been replaced as well as all four wheel cylinders, shoes and springs.  All bleeding good and adjusted shoes, no leaking and flex hoses good, drums look new. We used master cylinder PLC 753, and two sets of PLB 535 and PLB 536 wheel cylinders. All parts removed looked like what we put on, all four wheels look the same, with one adjuster per wheel. The car was refurbished 7 years ago and looks like they used what ever parts they had. The car's paper work said it is 1982, but don't think so. One question, what is different in the wheel cylinders PLB537 and PLB538 to the 535 and 536 that we used? Any idea on why the paddle goes to the floor?  We have run out of things to try, and any help would be greatly appreciated.