Old old craftsman that brake/clutch does not engage properly

I have a Craftsman LT1036 that up until now runs good. Yesterday after my son was mowing with it for about an hour, the clutch/brake pedal does not engage so that when you put it in gear, the mower does not move. If you take your foot and pull the pedal towards you then it moves. So it still runs and mows if you want to pull the pedal back with your foot while mowing!! Any suggestions to fix this?