Why do some gears on a Caterpillar 140H work intermittently while others shift to neutral?

[Elixer G]

I'm having a strange transmission issue with my Caterpillar 140H and hoping someone here has dealt with something similar. 1st gear works every time, and 5th and 8th usually work, but sometimes I have to shift back to park first before they engage properly. 2nd gear is the biggest problem because sometimes it bumps and immediately goes back to neutral.

 

[Harvey Esteban]

Had almost the same issue on a 140H before, turned out to be a transmission solenoid and wiring problem causing random neutral drops between gears.