actually my dad fishes that same reel and I have repaired it river side many times. pretty familiar with it actually. Last time something broke it was the spring that re-engages the spool after casting. I took it out and re-fashioned a new hook to the end and its been good since
I cant say what the problem is off the top of my head. taking it apart CAREFULLY and seeing how things function is how I problem solve it. unless a broken part falls out then its obvious.
when I say carefully I mean it. you take it apart to quick and things come apart you may not know how to put it back together. the older 5500/5501 have parts that need to go back in a certain order to work properly. a lot of the newer C3/C4 models its all fitted into a plastic piece which makes it a lot easier to work on or at least all 3 of my C3 models are like that