Classic/Antique Car Repair: 63 Nova clutch, clutch fork, clutch pedal

Question
Endplay on my 1963 3 spd., IL6 Nova clutch was suddenly to the floor.
I adjusted back to 3/4" and the next day, back to the floor.
Replaced the clutch set, reassembled, adjusted, and test drove - all good.
Went out for an errand and half a mile later, pedal right back to the floor.
I can think of nor do I see any reason for this to have happened.
What am I missing????????????????

Answer
Back in the day when this was a used car we ran into this problem a lot. There is a part of the linkage that we referred to as a "Z" bar. The rod from the clutch pedal comes down through the floor to a lever welded on to the "Z" bar. The shaft for the "Z" bar pivots on the frame side rail and on the engine block. On the other end of the "Z" bar there is another lever welded that has a rod that pushed the clutch fork. The welds on the levers start to let go and the clutch looses adjustment. Good luck, keep me posted.
Brad Sears