The first of these trucks I had was a 1951 GMC and the prior owner told me it had bad steering. As I recall, here's what I did in order: Adjusted the steering box. It didn't have much play at all. Bought a new drag link. They cost about $9 from NAPA back then and the original one looked like it had been used without grease a good while. Rebuilt the tie rod ends and adjusted toe in/toe out. And finally I replaced the kingpins, bushings and bearings. They were about $7 each side from JC Whitney and I think the machine shop charged me $10 for the labor. This all helped but it still wandered around like a drunk (even in city traffic). Finally (out of ideas) I counted the front spring leaves and noticed 2 had been removed on each side. Got a couple of complete springs at a junk yard, and when replacing them discovered the caster shims were gone. Result? The truck when I bought it had about a zero caster angle. It steered nice and easy but there was no reason for those wheels to want to straighten themselves. And because of that, no matter how good everything else was...the thing was doomed to always wander if left in that condition. As I recall, the shop manual called for 1 degree positive but I found adding 1/2 to 1 extra degree will make your front wheels more self-centering and cause it to wander a lot less. There is a happy medium and it may not be 1 degree is my message. Note: If you have too much positive caster, it will drive straight as an arrow, but it will feel heavy while turning and take more effort to steer. You have to sort of play around with this to find what you think is best. Also, I suspect too much caster angle will wear your kingpin bushings more rapidly. Look also at the rear springs and check to be sure nobody along the way raised the rear end and/or lowered the front end. Also check to be sure the prior owner wasn't running tires on the front which are a smaller diameter than the rear ones. Any of this stuff can reduce your caster angle. Good luck!
Jon
