Get under it and lube it with wd40 or some similar lube and work it back and forth.
Inspect the threads for dings and the shaft to see if it's bent.
Try it with the deck not quite all the way up. mid way, and not quite all the way down to see if it's binding only in a certain location.
Inspect the threads for dings and the shaft to see if it's bent.
Try it with the deck not quite all the way up. mid way, and not quite all the way down to see if it's binding only in a certain location.