An update on kingpin project, so others can learn.
In addition to worn kingpins, I've discovered the wheel bearings were too loose. When we started working on the kingpins, by removing the tires and rotors, I was able to move the tires and rotors back and forth on the spindles. A little bit of play is necessary to keep the bearings from wearing prematurely but this seemed like too much, and worn kingpins couldn't account for the amount of play.
The weight of the tires makes detecting actual play difficult. The rotors, by themselves without the tires, gives a better indication.
A bit of Internet research, focusing on heavy duty trucks, led to examine two indicators. (Yes, what I'm working on a light truck but information on heavy duty trucks tends to be more consistant and provided by professionals rather than a lot of amateurs or shadetree mechanics who may not know as much.)
The two indicators are tire tread and brake lining wear. Loose bearings, according to the professionals, cause the hubs to lean inward at the top, when the vehicle is lowered to the ground and weight is applied to the spindles and hubs.
The inward lean causes the inside edges of the tire tread to wear more. Likewise, the lean tends to cause brake linings to wear unevenly. In our case, the tread wear was as predicted. Likewise, the brake pads were worn to a taper rather than evenly across their length.
Further web exploration indicated the old Haynes manual we were relying on has an apparent error in terms of the wheel bearing preload torque specification. Everything I could find on the web indicate the actual torque should be two to six times what is in that manual.
The HD truck procedures indicate the hub play should be between .001" and .005" and a final check should be done with a dial indicator.
I have a dial indicator and accessories but most people in this thread probably don't. There's plenty of guidance on how to (re)pack, install, and preload bearings so I won't get into it. However, the range of recommended freeplay is roughly the width of two human hairs. So, if you can detect freeplay, your bearings are probably too loose. (If you have significant difficulty rotating the hub or tire when it's off the ground, then your bearings may be too tight.)
Old-timers guidance, from almost 45 years ago, says tighten the spindle nut until you can't turn the hub and then back off the nut 1/8 to 1/4 turn. Calculations, based on typical spindle thread count, indicate this should be close to recommended freeplay. (There's actually more steps involved so do your research. I'm just focusing on diagnosis and calculations here, without regard to what is take to do the job correctly.)
