T20 Transmission Repair

Today I set out on diagnosing and repairing the T20 Transmission in my Hustler 6×6.

The symptoms I had noticed were a grinding noise when turning left and an inability to go into reverse. Although I thought the only reason I couldn’t get it in reverse was the fact one of the shift arms was striking the solenoid on the new engine I had put in.

When I pulled the bottom plug on the transmission, oil flowed out for quite some time. It appeared to be gear oil. So it was obvious someone had filled the transmission from the vent plug with gear oil, instead of ATF. So I had pumped the remaining oil out and filled with the proper levels of ATF and friction modifier. It was after all of this that I noticed the symptoms listed above.

I expected to find that the bands had been damaged and possibly the drums. So I purchased a body gasket from Max6x6 and planned on pulling the transmission and splitting it to see what all I needed to order.

Before starting the removal process, I decided to pull the diamond shift levers out just to make sure they were in good shape. This turned out to be a very good idea. The right one was still in good shape and I just cleaned it and put it back in. The left one had a flat spot worn on the pin.

I put the pin in my vise, using some aluminum to prevent damaging further and was able to rotate the pin back and forth, until I could pull it free from the plunger. Since the pin is symmetrical, I decided to use a file to clean up the damaged end and reinsert it with the other side of the pin up.

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In the event I need to have some of these pins made, I captured the measurements in the photos above.

I then cut off about 1/2″ of the shift rod so it wouldn’t strike the solenoid. I re-installed the shifter and to my surprise, the transmission worked perfectly with no grinding or noises at all! I was very happy. I may still decide to tear into the T20 later to do some preventative maintenance but for now it’s on to other things.