[racingdwarf]

If you have a a total and dramatic failure I wonder if you have stripped the little lugs of in the diff nut holder or your nut is spinning in the holder, or the holder has split. I'd be surprised if you had broken the screw before destroying those parts! the nut holders have got a little history of problems, but my 1st 22 the nut holder was a bit of a git(a known problem) but the two cars I run now for the boys are faultless

Also as has been said if you are having to tighten it so hard check you have correct assembly