I recently purchased a pricy zero-steer riding lawnmower from Troy-Bilt, a Mustang with a 50-inch deck. The design is such that there are two independent hydrostatic drives to each of the rear wheels, enabling the zero-steer capability.
After approximately seven hours of use, I started to lose torque to one of the wheels. Concerned, I jacked up the mower, crawled under it, and found that the drive belt had a twist in it. The drive belts on riding mowers are simply V-belts routed around a series of pulleys. One belt supplies power to the drive wheels and another supplies power to the mower deck. Since the machine was assembled by employees at the store where I bought it, I figured this was just an oversight. I corrected the belt and was back on my way.
It didn't take long for the condition to repeat itself. With the belt corrected, I feared that one of the expensive hydrostatic drives had gone bad. It was severe enough that I would have to have the unit repaired. This did not sit well.
I decided to try fixing it myself before I went through all the time and expense to return the unit for repair. I went online to see if there were any threads referring to hydrostatic drive slippage on riding mowers. There were some that talked about the oil getting low and causing the problem. I then checked my manual to find that my drives were sealed, so there would be no oil leak, and they wouldnt need to be topped off. I then did some testing of the drive system on a steep hill to ensure that it was only the one drive that was having a problem. I found that the other side was also having a problem, but it was not as bad as the initial side causing the issue. That was actually good news. I couldn't imagine that both independent drives would go bad at the same time and after only seven hours of use.
Since I have a car lift, I lifted the mower up in order to get a better look at the drive belt system. I was getting the feeling that it was the culprit. Since the drive belt is routed from the engine pulley to one side drive and then the other, it is possible that if it were slipping, then the side closest to the engine drive pulley would slip the least and the conditions that I was witnessing could be explained.
When I looked at the drive belt again, it was once again twisted. No blaming it on the store employees this time. I then noticed that the tensioner arm sat very close to a bolt head that was underneath the engine securing the engine to the frame. I manually articulated the tensioner and found that the tensioner arm could hit the bolt head, which would cause a momentary loss of tension on the drive belt, allowing the belt to twist and lose its tractive power! What a huge blunder!
It was a miracle that I found a button head bolt exactly the same size in my shop to replace the standard hex head. This way, there would be nothing for the tensioner arm to hang up on. I also radiused the tensioner arm with a grinder so that there were no sharp edges to catch on anything else. Finally, I got a new belt, one that was a little bit shorter than the original, to help pull the tensioner away from the trouble area and give more tension on the belt.
After spending several hours of my time fixing something that shouldn't need to be fixed, I can say that the mower is now better than new.
This entry was submitted by Chris Clouser and edited by Rob Spiegel.
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