'83 kz1100 stuck in 3rd gear

Hey guys, first time posting, long time lurker. I have a 1983 KZ1100(with a sidecar) , I was just riding down the road and it made a light clunk noise and wouldn't shift out of 3rd gear. Well, I'm pretty sure it's third. Slim possibility its 2nd or 4th. The clutch engages/ disengages, but that's about it. Any direction to get this corrected would be greatly appreciated. Thanks in advance!

Are you rolling the motorcycle or spinning the rear wheel while trying to change gears? the Rr wheel needs to spin to shift.
If you're certain the clutch adjustment is good, the Kawasaki service manual lists a number of possibilities in the Troubleshooting section.

Check the gear lever return spring behing the front sprocket trans cover.
This is the most likely culprit for an out of the blue engagment problem with no previous warning.

Broken return spring is a common issue. Damn near impossible to shift without it.
Steve

It's a shaft drive, if that makes any difference. It's an ltd, I've always thought it was a KZ... might be wrong. I pulled the cover, seems I have to pull the shaft to go any farther.

Yes! you will need to remove the bevel box to access the return spring.
If the spring has broken the lever won't return to the center position ready to hook another pin on the selector drum.
You will feel that the lever is loose in the hand and may have dropped to it's lowest position.
Unless the broken spring has jammed the lever you will be able to manually return it to the center to select another gear.
There are of course other possible causes for your issue but this is the least invasive and easiest to fix.
If this is not the problem the next course of action is to remove the sump to inspect the selector forks etc .

I don't believe it's the return spring, the lever will push down and spring back to center, but will not push up.

Will it shift up while moving?
Steve

It would have to be in first not to engage a higher gear at standstill because of the neutral finder.
Try rotating the back wheel while the bike is on the main stand to engage another gear if it is already in second or above.
It is also possible that the bolt in the 3rd gear fork that locates it on the drum has become loose and unscrewed.
This could also cause the same issues but can also allow two gears to be selected at the same time locking the transmission and destroying gearbox.
I would double check the lever again and if no other gears can be selected you have no choice but to start behind the bevel box then dig deeper until the problem is found..

No it will not shift while moving. It's not in first, because I can ride it the way it is, but I have to hold the clutch in until I get up to a reasonable speed, otherwise it bogs down, which tells me I'm in a higher gear. Also, when it did get stuck, I know I wasn't in 1st gear. I need to get a manual, because I hate tearing this deep into something like this without some guidance. Inadvertantly I did roll the wheel backwards last night, to get it out of the storage spot I had it in. Still wouldn't shift.

Looks like you will need to start at the selector mech and move deeper until the fault is found..
These engines are simple devices with little more than basic competence needed to strip and rebuild them.
Very little goes wrong with them with most issues being inflicted by previous owner incompetence.

Ok, so it looks like I need to pull the rear wheel to get the shaft out. Correct? I guess that's what's hanging me up,I just want to make sure I'm not doing extra work if there's an easier way