If it grinds the synchro rings are shot I am not familiar with the inside of ax15 but most synchro rings are only brass and dont have full teeth like a normal gear

Yeah, agreed with the other poster, its just a simple synchro gear, or maybe even just a worndown gear. It's worth it to fix it, as long as the truck price is right. tearing apart the ax-15 isn't bad, just make sure to keep measurement right, aka parts in order. The synchro gears aren't to expensive, and its a day or two project, again, what we love about jeeps. Good luck.

I found an AX-15 manual and there is no syncro on reverse.

x2 no syncro for reverse. Its either the reverse gear in the trans is bad, not to bad to fix if your comfortable opening the trans or there is a clutch issue

Well that idea has flopped, I was planning on going to get the truck this today.
I asked my son again this morning what he wanted, we was looking at two trucks.
the MJ and a Nissan Hardbody, the nissan has timing chain issue, but only 108k miles.
The MJ has some rust and 240k miles.
The Hardbody won out so I'm going to get it shortly and get to learn the ins and outs
of working on a KA24E nissan engine.

SR20 swap...

Moved to OEM Tech.

Im pretty sure every ax 15 grinds in reverse. It does not have a scychro. So make sure you are stopped before shifting and do one of two things to stop the grind shift into any forward gear (1-5 is fine) I prefer 5th gear and then straight to reverse or hold the clutch in for at least 10 seconds and then shift to reverse.

I agree with this! Also my ax 15 doesn't really grind but sometimes it won't go into reverse very easy, a quick shift into a forward gear and it goes right in.

It doesn't really have a fork per say but rather a linkage. It's highly unlikely that's the issue.

I agree with your second thought, I bet its clutch related rather than a "bad" gear. Straight cut gears don't like shafts that won't stop. True story.

I like the way you think, except for that first post in here... not a one word of that was correct.

You're gonna hate that Nissan man, they're so gutless. I almost pulled the trigger on a V6 hard-body and even that one blew with stock tires...

sometimes mine does that, but if I modulate the clutch and let it roll a little sometimes it will engage

try that first before tearing into it

My bad. I knew with forward gears, but at least i acknowledged it could be the gear and not the synchro... Anywho, good luck with the Nissan