If it will shift into any other gear, your issue is with the shift position sensor or something mechanical. To narrow it down, use the manual actuation of the shift motor in the diag screen. The combine engine will have to be off to do this. Have somebody watch the shift position on the indicator on the top of the trans while you press the touch screen to manually actuate it. Watch the amp bar graph, when it goes way up, let up on the button immediately - you will blow a fuse if you hold it too long. It should be possible to move it from 1st to 4th this way. If it will not move all the way, it is most likely mechanical and requires internal investigation. If you can get it to move all the way, both ways, check the shift position sensor (the kidney bean shaped thing on top of the transmission). If it doesn't sense that it is in a gear, it won't let you go in that gear to protect the transmission, and for safety. These do go bad. They are comprised of five separate switches and one can go bad while the others continue to operate.
I appreciate the second opinion on being mechanical inside the transmission. When I removed the shift motor and turned the nut under where the shift motor is it will go easily into every gear but first. My neighbor did have the shift position sensors go bad but he could shift it manually into the gear he needed. Trying to finish up corn harvest on frost and broke through. Needed 1st gear to back out. I was hoping it wasn't internal since that is not as easy of a fix. Has anyone removed the hydro transmission on an 7010/8010 or CR combine? This is a 2004 model year 8010.
Removing it is not a terrible job, the thing is just really heavy. I'm not sure that I'd want to do the job out in the field. Without knowing more, I'd sure suspect electrical before mechanical based on my past experience.
I wouldn't think about doing something like that out in the field. We got it out by pulling it. We are sidelined for now waiting on more frost or until I get 1st gear back. I like the diagnostic screens on the pro 600 monitor. Do you really think it could be electrical if it doesn't want to go in manually? It feels like something is binding inside the transmission. My dealer says that there is some info on ASSIST about mechanical problems inside. I will probably drive the combine to their shop to work on it.