Hi,
If you weld this, it *will* bust again with 100% certainty. I'll tell you when it'll let go, too.
When you're digging a fundation, or swimming pool, or some other reason for making a large hole in the ground, which is a good use for a dozer.
At some point, you'll be pushing a blade full of dirt up the hill you've created. As you hit the point where the original grade is, the front of the tracks will be onto the looser dirt you've already pushed into a hill. The change in density will cause the machine to rotate a bit as the traction conditions change.
This will put most of the weight of the machine on the final drive that's more downhill and still at the point of the original grade. It will also put the weight of the dirt on the blade onto that final as well. Since that track will have more grip than the other, it'll put most of the power onto that sprocket as well.
You have a 50/50 chance of this being the repaired housing.
So now we have all this weight on one housing, plus some side torque from the twisting of the whole machine on the housing, plus the torque of the engine going through that sprocket. Oh, and all this also causes the track chain to bunch up a bit and yank forward on the sprocket as well.
Crack.
Now, the machine will wind up back in the hole, with one track shucked off. Well it will if you have the usual luck as to when dozers break.
I can tell you how the original crack started as well. Someone went too fast over a log (or rock or whatever) in reverse and slammed the back end down hard. That can start the initial crack very easily. They probably had some loose bolts to go along with it, too. Sigh.
Once the tiny crack started, then various torques and loads made it get larger until we have what you see. What I see in the pix is about six attempts at fixing it by welding only to have it get worse each time.
If you intend to fix this and just take it to shows, you *may* get away with welding it. Although, you'd best be careful putting it onto the trailer. They like to slam down on the finals and that's something you need to avoid with a weleded housing like that.
Sometimes I wonder if the welder's head happens to be harder than the material he's trying to weld. I think that's the case here, I'm sorry to say.
Here's an idea for when the weld breaks: Go into the machine shop, grab a large chunk of steel, head to the large mill - and cut away everything that doesn't look like a final drive housing. I know that'll hold up!
Or, buy another old cast housing that ain't cracked......
Later (and best of luck to you),
Stan