If the screw threads do not rise above the locking nut then STOP: The steering box is worn out, it is time to rebuild it, or replace it! Failure to do so could result in your steering system failing.

Loosen the Locking nut, so the set screw can be turned with a flat head screwdriver.

With the wheels straight and the steering wheel centered. Turn the lash adjustment screw clockwise until it stops, but don't force it any farther!

Making sure that the screw does not turn, carefully tighten the locking nut.