Kingpin bushing replacement

The kingpin bushing, even new and tight, is also ineffective at stopping the front axle from
attempting to pivot in a horizontal plane about a vertical axis (the way a kid's wagon steers). The 1/2 inch lever arm at the pivot doesn't compare well with the 30 inch long axle arm.
Your radius rods take are supposed to take care of limiting this motion.

The "excess motion" that a new kingpin bushing will fix is anything perpendicular to the bushing (up and down, and side-to-side.) It is this motion, when it gets bad enough and combined with the other, normal motions, that breaks distributor caps, hits radiators, or pushes the fan shroud into the fan.

One way to diagnose the need for such repair, aside from taking it apart and measuring, is to jack up the tractor under the oilpan until it is just possible to pivot the axle and get both wheels off the ground, letting the axle hang from its own weight. Now lift up on one end of the front axle. Observe how much "lost motion" occurrs at the center pivot pin as the other tire contacts the ground and you continue to lift the axle. Also, try to slide the axle directly sideways. It has to be a pretty noticeable "clunk" in at least one direction before fixing it is going to do much for you.

One other thing, there is supposed to be some play in the axle to allow movement of the axle. The radius rods are designed to keep the axle from twisting. The axle needs to be able to move when you adjust the tread width.

And like someone else said, there are no replacement pins for the early Ns, you have to rebuild or make a new one if the old is too far gone.

This from my experience, yours may vary.

The arms usually called "radius arms" are absolutely key to proper front end geometry. They are supposed to be straight, and kept straight. They provide what little control Ford has for the front end alignment element called 'castor'.

The radius arms move in an arc some as the front wheel track is set wider or narrower. Because the radius arms are fixed length, this wheel track adjustment causes the front axle to move a bit forward or back... another reason NOT to shim movement out at the center bushing.

If you have up and down movement at the center bushing, you may want or need to replace the bushing and/or the pin. But be sure the radius arms are straight, that they are not too loose where they attach to the outer axle portions and maybe even shim the play out of the rear ball socket.

Just my thoughts of Ford front axles.