OK I'm new here so bear with me!! There is a small keyway in the bottom of the sled, its by the bottom of the clutch and screws into the crank. When water gets into there (its has a grease fitting on it) its usually freezes and then when you take off again it snaps. You will have to unscrew it from the back and take out the hole bottom shaft and replace the keyway. Ant more questions let me know.
What Harder is talking about is the square piece[2"to3"] of speedo cable in the end of the main track drive shaft.If you take the 3- 5/16" bolts out &remove the cover you can check.Some times if it's not dry or froze ,the main shaft bearing is bad.With luck it only froze.