Here's the way we did it in a professional front end shop for a lot of years. It's a little tedious, but it's very accurate. Start by disconnecting the steering gear from the rest of the system by removing the Pitman arm, or otherwise isolating the steering gear. Count the number of turns of the steering wheel lock-to-lock, and turn it back halfway. This should be very close to the "center point", the area of minimum clearance between the worm and sector gear. Adapt an inch-pound torque wrench to the center nut on the steering wheel. (This usually involves enough socket adapters to allow a 1/4" drive torque wrench to turn a nut about 7/8" in size.) Using the torque wrench, start turning the wheel about 1/2 turn from the center point, and turn it through center, watching the torque reading. It should rise about 10 inch pounds as the gear moves across center. For instance, if it takes 10 in/lbs to move the wheel when it's off center, it should rise to 20 in/lbs as it goes over center, and drop to 10 again after it passes the center point. If it rises, drops at the center, rises again, and then drops, the worm gear is worn out and the gear needs replacing. The preload is changed by tightening the sector gear adjustment, and locking it in place with the locknut when the preload is correct. The wheels should be adjusted to point straight forward when the steering gear is on the center point. This can be done by using a string stretched from front to rear wheels, and connecting the steering linkage when the wheels are pointing straight ahead, and the gear is center-pointed. Lots of work, but worth it!
Jerry
