Tore up the PTO shaft on my finish mower this past summer when using it on my 8N.
The 3PH on the 8N sometimes gets a mind of its own to just raise up to it's maximum travel even though you don't have the position control lever set anywhere near that.
So anyway, I'm mowing grass, and just finish one section of the yard. I raise up the mower about 6" or so, and start heading for the back section of the yard, with the PTO still running (the hitch leaks down in about minute unless you keep the PTO spinning). I get about halfway there, and all of a sudden I hear the loudest, most violent commotion going on behind me...
... the 3PH lifted up to it's maximum possible height, and hyperextended the PTO shaft with it spinning at rated speed. That was a set of nun-chucks spinning around back there like you've never seen before!!
It took me about 3 hours of heating and bending and tweaking with the torch, hammers, wrenches, etc, getting that shaft back in shape enough to get it back together again. That was probably the 4th or 5th time that's happened... but it was the first time that it happened at that speed... and the first time it did any real damage.
That day it was decided by me that the 8N was going to get replaced regardless of what "she who must be obeyed" said... and my new Mahindra was sitting in the shed a few days later
!! It's much easier to beg for forgiveness than to get permission sometimes... and you just have to do what you have to do.
Also had to replace that PTO shaft... at the length it had to be to work with the 8N, it was way too short to work on the Mahindra.
Don't get me wrong, I love my 8N, and it was a great tractor in it's day. Unfortunately, it's day was about 60 years ago...
Also, I just remembered, I had to replace a spindle on the same finish mower... the top bearing in it failed and was making quite a racket, but at least it didn't take anything out with it.