Wow.....A YJ with manual steering? Was it upgraded to manual? Regardless, either type of gearbox can be adjusted for lash. Lash or backlash being the distance or angle of the gear teeth inside the box. If you look at the top of the gearbox, there will be a adjustment nut assembly (a nut with a slotted shaft or Allen-head screw in the center). Use a screw driver or Allen wrench to hold the center shaft in place while using a wrench (1/2 or 9/16?) to loosen the locknut (counter-clockwise) just slightly. Turn the center shaft clockwise (while hold the locknut in place) a 1/8[SUP]th[/SUP] of inch at a time while checking the amount of play you still have. Tighten down the locknut (while holding the center shaft in place) before trying to turn the wheel again. If the adjustment shaft binds or tops out, back it off slightly. If you reach the point of binding and achieve no lash adjustment, it’s time for a rebuild or replacement of the gear.
Go slow, and CHECK YOUR WORK! If you forget to tighten the locknut down or bind the gears, this can lead to a catastrophic failure during the test drive. With all this said, please check all your associated linkage as well....I.E, the shaft couplings, bushings, tie rods and drag link for play or weakness. It likely you have something else loose or out of spec. causing the gearbox to loosen up. If you have a helper around, get them to turn (or try to anyway) the wheel while you watch the steering linkage. Look for loose joints etc. While the gearbox and linkages are under load.