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Problem with Sunstar/Ultima Transaxle

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Good morning everyone,  I have hit a snag with the transaxle on my Sunstar/Ultima. I am hoping it is a simple fix! 

I was using my tractor to plow last weekend and it ran fine. However now when I fired it up to plow earlier this week, the left wheel would only move in forward. When I put it in reverse the LH wheel locks up and all the power goes to the RH wheel. I jacked up the back end of the machine and put it in neutral (HI/Lo selector in middle). The RH wheel spins freely and the left still does the same, kinda moves in forward but locks up in reverse. The tractor has individual brakes, diff lock as well as HI/LO

I am going to take the wheel off this weekend and inspect the brakes to see if something is binding in that respect, however my mind keeps jumping to an internal issue to the trans. 

Any insight would be much appreciated, thanks! 

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If the differential gears were bad I'd expect free-wheeling or chunky/clunky engagement when trying to spin one versus the other. I'd lean toward a brake issue on the side that doesn't want to go backwards. A bad axle bearing could cause that too, but when was the last time anybody saw one of those fail????

Edited by RAC

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RAC, I got it figured out last night. I went to remove the brake drum and noticed that the axle nut was loose when I went to take it apart. Didnt see anything very out of the ordinary aside from the back brake shoe being misaligned. I put it back where it was supposed to go and torqued down the axle nut. After that everything was happy and got to working again. Thank you for the help! 

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