Look at some of the youtube videos on servicing Singer foot pedals. As they get older they can get stuck (sort of). The videos are very explanatory. It's an easy fix, you just take it apart, clean it up and adjust it. All the old Singer foot pedals are the same. I'm assuming you know that your foot pedal is inside the knee lever apparatus. Just push it up and the pedal will come out. When you put it back, just push it down in the bracket.
bkay