You are going to have to have someone move the wheel back and forth and look for the play in the linkage. It usually isn't the steering box, it could be any one or several of the tie rod ends, drag link, ball joints (if you have them), spring shackles (if you have leaf springs), king pins (if you have them), or wheel bearings. Its usually pretty obvious. If the play is that bad its likely that all of the front suspension is worn.

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