So, you now have an explanation of what went wrong with the mower, and it is something that should be fairly easily fixable. Just be glad it doesn't have a Posi-Traction car differential - I once twisted off an axle shaft at the inner end with one of those, and unfortunately some of the twist occurred in between the side gear and the clutch hub, so it could not be dismantled. Of course I did dismantle it - I drove the twisted stub right through both the side gear and the clutch hub by sustained use of a three pound hammer, since I didn't have a press at the time. Hardest part was getting the diff center out of the rear axle housing (it was a banjo axle). The broken axle stub stuck out far enough to prevent the diff center from coming out. Cunning use of levers eventually overcame the problem. Of course it would have been better to scrap the whole rear axle, but unfortunately the diff center was a heavily modified one that I couldn't replace. But I digress.
I agree Ken, PMing Bruce is the way to go. That axle is an expensive piece of gear, and working on it with a manual beside you is way safer than improvising. Doing it by ear is OK when you have no choice, but doing it by the book is much less stressful.
