I just rebuilt an AX-5 tranny on my 90 YJ. It's not too difficult. I would suggest taking pictures during disassembly to help with assembly. Haynes manual has some exploded views of the AX-5 tranny. I also went to O'Reilly'
s Auto Parts and bought a credit card sized entry authorization for Mitchell Online. The card was only $3.99 for a one week entry authorization, and printed out all their info. and pictures of the AX-5, which helped out a lot regarding the balls and springs and detent pins located in the cast-iron middle portion of the tranny. I bought the re-build kit off of E-Bay for around $125, and the bearings were the exact same brand that I removed from the tranny. The vendors name was ACERL. The synchros are also identical. I just got mine back on the road, and am happy to say everything is OK. I replaced the clutch, pressure plate, and throw out bearing assy. while I had it apart.
If the 5th gear shifting fork is wore out and not coming out of 5th gear completely, it will prevent Reverse from working correctly also. The 5th gear cluster is on the back side of the tranny, so it will be easy to diagnose.