The transmission is an AX5. There is a retaining clip that holds the fifth gear in place. It is a common issue for the clip to break and for the gear to move back on the main shaft it the transmission. You should be able to run it like that but you will not have 5th gear until someone pulls the trans apart and puts a new retaining clip in.
84 CJ7 Northstar V8
91 YJ Renegade, I have owned it since it was new.
Jeeps that I am currently parting out;
199 Jeep TJ 4cyl 5spd
1988 Jeep YJ 6cyl 5spd
1984 Jeep CJ7 6cyl 4spd