It was beautiful today, highs in the upper 50s. Perfect for cutting grass in a sweatshirt. I was actually enjoying cutting the lawn when I heard a pop and the mower stopped moving. It wouldn't go forward or in reverse. I assumed a belt broke or something. I looked underneath hoping the problem was obvious and something I could fix. Nope, no broken belts. I read the owner's manual troubleshooting page and under Mower Won't Move it said the parking break was on. Duh. No it wasn't but I needed a break. It was kind of hot to touch so I thought I'd let it cool off while I had lunch. With a full stomach I was ready to spend a little more time looking. It didn't take long to discover a small but heavy duty looking spring dangling near the back. It looked like this.
This is where I hit myself in the forehead and say, "wow, I could've had a V8". Maybe you know what I mean. Of course, the answer was obvious. Google it. I did. I typed in John Deere GT235 won't go forward and came to a few forums. On one of them someone mentioned the idler arm tension spring. Next I Googled John Deere idler arm tension spring and came upon the answer I was looking for in this link http://outdoorpowerinfo.com/repairs/deere_lx266_hydro_belts.asp On this page you could click on the pictures and it showed you the bottom of the mower, which you can't see because of the mower deck on your own. I went back out to the mower and, sure enough, saw exactly where I needed to hook the other end. Too bad the spring is so short and thick and it has to stretch 18 inches (Edit: it doesn't have to stretch 18 inches, only about an inch. I had it in the wrong spot). All I need now is my sidekick to help me stretch it so I can latch it onto the idler arm.
I hope this helps someone else who has the same problem and Googles it.