Clutch problem

I have an 87 chevy s10 4 cylinder manual trans. With about 170,000 miles on it. Today, my clutch slipped badly and stopped shifting while the truck was on, but when I turned the truck off I could shift into any gear perfectly. The clutch pushes down very easily and comes back up. I think the problem is a broken, lost, or loose bolt on the clutch arm but I can't find the clutch arm. I know I have a lot of miles and I should probably get a new clutch since I haven't ever replaced it but, I don't think I need one. If you know where the clutch arm is or have any other suggestions please let me know.