I recently aquire a MF 12 with a standard 4 speed transmission. The gear shifter will not move any of the gears in the transmission. It is currently in neutral as the engine can be started and the tractor pushed around. Any ideas?
It sounds like the shift rails are frozen with rust. Had a similar problem on another Peerless 2300. On that one I drained the gear oil and refilled it with diesel and ran the engine briefly to make sure it circulated the diesel throughout the transmission. Make sure that the Vari Drive is engaged when you run the engine as the input shaft must be turning to distribute the diesel. About a week or so later the shifter finally broke loose with a little effort. Drove it around a bit afterwards with the diesel still in it then drained and refilled with gear oil.
If the above doesn't work you will most likely have to pull the transmission and remove the shifter for access to the shift rails. Good luck!
Hopefully when you drain the transmission, it doesn't look like muddy river water like the one I took apart last year. The MF10-12 repair manual shows how to take apart the transmission. There is also a Peerless transmission repair manual you can down load with more pictures on rebuilding the transmission.