Not a cat but I need help

I have a customer with a John Deere 455c track loader that will not move in reverse. I haven't Been to look at it yet, but does anyone have any ideas?

Check the shifter linkage very carefully. If it's anything like the ag tractors, moving the shifter from forward sector to reverse sector moves a linkage or cable to shift a valve. If the cable is broken or the shifter worn from going between forward and reverse many times over the life of the tractor, you may not get it to go in reverse.

If that all appears satisfactory, then a set of pressure gauges is usually the best way to diagnose a powershift. You could also start by changing and cutting open transmission filters to check for debris from clutch packs etc.