rupp rat rear end problems. please help?

#1
OK so I got a rupp rat I think!! That's what the guy told me it was anyway. The jackshaft was bent so I replaced it. Started it up and went around the house once and it popped and now the differential spins and the axles don't. I'm going to take it apart tomorrow and pull it apart but wanted to know if anyone knew anything about em. Is there a shear pin or could it be a broken gear? Idk I've never messed with one and its the first I've ever seen. Anyone with some knowledge please help me out. Also here's a pic. The front end has been changed to a Honda 250 front end but that's all that's been changed from what I've seen.
 
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