Howdy,

You can eliminate some minor lash with the screwdriver adjustment. The nut around it is a lock nut; loosen that, adjust with the screw. Be careful though -- you can overtighten that adjustment and accelerate wear on the worm gear. You will be able to feel this in the steering wheel as excessive drag -- hard to steer; correct immediately. Be sure to top-off the steering box with gear oil anytime you service it.

You should have about 1 to 2 inches of "play" in the steering wheel. More than that indicates wear but it is not necessarily the gear box that is the problem.

Be sure to check the complete steering system before adjusting the steering box. Play in the pitman arm, tie rods, and idler arm can all add-up. Your box may be just fine; worn tie rods and a sloppy idler arm are more likely than a worn steering box.
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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 52 year old fat man. ;-)