Took the 1850 for a small jog to pick up the wife who was going to ride with me. Stopped, applied the brakes and when I tried to move again, the transmission froze. Basically it would kill the motor whether it was in gear or not. I understand the issue is probably the upper transmission shaft. My question pertains to the potential parts to be used. This is a 1968 with a 3 speed. I have an older 1850 (not sure on the year) and a few of the 55 series tractors, including a 1755, 1855 and 1955. Are these shafts basically interchangeable or do I have to look for something in the same model and year? Not looking forward to this project and it seems the projects are lining up faster than they can be fixed..