You missed at least one cause.I did find a way to search this specific thread. See attached.
The search for splitter in the parent unimog thread is https://www.steelsoldiers.com/searc...t=post&c[child_nodes]=1&c[nodes]=34&o=date for anyone else who is looking.
I will perform another search using the manual's terms, "intermediate speed control".
I read all the ones about the intermediate speed control air shift splitter, most of them are people posting w/o a path they took to diagnose it.
Iit sounds like it could be stuck in between gears. I was distracted and at a total stand still shifted the air splitter without clutch engaged, I think I was in neutral at that time. But I moved it after that w/o any issues so I'm not sure that did anything. I think when I tried to move it unsuccessfully after that I had moved the splitter and at that point I think it got stuck.
I let the air pressure build to over 90. I moved the air splitter up and down a few times, no luck.
I'm not 100% certain, but I recall hearing more of a noticeable shifting sound on the air shifter when I moved it in times past when driving. Now it seems to just make a little air sound and I don't hear that "ok, I've shifted now" sound.
Things I've gleaned that could be wrong:
1. clutch (I don't think so, it worked fine when I parked it) but will diagnose with the rear PTO test. I read if the rear PTO works your clutch works.
2. Some people wrote they have air shifter issues like this that come and go. No solution was provided where this is mentioned.
3. Stuck "overflow" valve could apparently cause this. The primary (I guess brake) air system has to have enough pressure before it will overflow the pressure to the shifting system.
4. Splitter solenoid could have gone bad suddenly.
5. There could be a fuse problem depriving power at the solenoid. I did lose a fuse (presumably) the other day as all my dash gauges went out, so I will check this first.
6. Rust in the crossover air line contaminates the air system and plugs solenoids, filters, lines. This is a known issue and covered in the PS magazine articles.