Seems to me that my 6501c3 will start to bind a little when on the water sometimes, but it goes away with a little lube on the levelwind whenever I'm fishing. Everytime I finish fishing I rinse my reels with the freshwater taps at the pier, so I doubt it's corrosion, but why does the free spool become all wonky when I'm fishing? I lube my reel bearings and levelwind with old abu oil in the tubes. Is that causing the problems? Used to use air tool oil and it seems that worked, but what am I missing here?
Start by cleaning and degreasing the entire LW system, then use only 1 drop of oil, preferably TSI.
Check the line guide pawl. They can get worn to the point that they hang up in the worm gear. Running the reel in this condition can damage the worm gear also.
Tom
The line guide carriage can also become worn from riding back and forth on the worm. If it is worn it will not run true and may bind.
Start by doing what Keta/Lee says above. If that doesn't work then look for new parts.
Levelwind problems are difficult to diagnose because they often feel smooth and normal on the bench and do not bind until you start putting some lateral pressure on the line guide in the field.
-steve