|was pushing the major forward in the workshop the other day just after finishing the full engine rebuild and felt a tight spot when it was in neutral so decided to investigate and this is what I found.....
ever seen these crack like that before? took me a while to find a new one so I did the gaskets and cleaned the backend out in the meantime
the new secondhand drive gear with the old bearing and race off the broken gear the bearing had no wear at all so it was re used
Those final reduction gears are extremely chunky. They have to be as they take all the drive in one short section of their circumference at any given point in time. Surprising to see such a crack. Maybe a flaw in the casting?
Beautiful job you've made of the overhaul. The fresh oil you put in the rear end is going to have a lovely clean home.
Best
Adrian
Just wondering if this is diff related. With one wheel slipping and spinning, the diff is activated. The spinning wheel effectively becomes a large flywheel. If the operator were to stamp on the diff lock pedal under such circumstances, and the diff lock managed to engage, then all of the momentum from the spinning wheel would be transferred in an instant to the stationary bull pinion and give the final reduction gear a sudden shock.
Best
Adrian
When you look at the csa of the root as opposed to the tooth under load its surprising the tooth didn't snap off, must have been some stress raiser in the root for that to fracture - still it shows the effectiveness of drilling the end of a fracture to stop it going any further - I hope you can lay hands on a spare
Best regards
Rick - Bogside on Bure
1958 Diesel E1A Mk2 s/n 1470165 - still in working clothes
My theory was a flaw in the casting as the steel in the crack under close inspection appears black I only noticed it due it catching the diff/not meshing with the diff properly and that was when I was pushing it by hand in the workshop so no idea how long it has been running with the split in it doesn't appear to have damaged the diff at all fingers crossed on that one. got the new gear in today a neighbour happened to have an old one sitting in the loft needed a good clean down but it was the right size and all reassembled turns nicely now no stiff point just waiting for my large order of oil to be ready got GB oils to make me some up and we will be in business hopefully want the major done for hay time to do some nice work to get everything settled in nicely and start breaking in the engine
Glad you've got a replacement on hand, black in the crack = old break but I've no idea if you can tell how old - by the gap it looks like a fair bit of tension left in it.
The fact you detected it by the tight spot is a good indication that the mating gear is not worn enough to accomodate the small change in tooth pitch the gap introduced.
Should be a reliable haymaking from the back end after the job you've done
Best regards
Rick - Bogside on Bure
1958 Diesel E1A Mk2 s/n 1470165 - still in working clothes
I only noticed it due it catching the diff/not meshing with the diff properly and that was when I was pushing it by hand in the workshop so no idea how long it has been running with the split in it doesn't appear to have damaged the diff at all fingers crossed on that one. got the new gear in today a neighbour happened to have an old one sitting in the loft needed a good clean down but it was the right size and all reassembled turns nicely now no stiff point 
just waiting for my large order of oil to be ready got GB oils to make me some up and we will be in business hopefully 