Make sure that you keep the towball locking shaft absolutely spotlessly clean otherwise the slightest debris will affect the locking efficiency which is what has happened causing the mechanism to jam up. It is also important to refit the protective hole cover afterwards for exactly the same reason and advised NOT to grease either components as this is a magnet for attracting dirt particles.
Thanks for this but I do use the protective hole cover I wondered if it had anything to do with the salt because of the snow. There was some rust on the bottom where the 2 parts meet. I have out some spray grease on as I didn't think about The implications of dirt
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