I just took my '50 out for a 100 mile trip and had to hit the brakes pretty hard and the steering wheel pulled hard to the right. It never did that before. When I got back home, I jacked up the left side and found way too much movement when I grasped the top and bottom of the tire. Worn kingpin.
You say that you have 40,000 miles on your kingpins. That is a lot of miles believe it or not. The Book says to grease them every 1,000 miles. I have never grease them that often. I wonder if anyone does (except for Denny Graham).
Check yours out. Jack it up and grasp the tire at the sides and feel for movement. If it moves, its probably loose wheel bearings.
Now grasp the tire at top and bottom and try to feel movement. If the brake backing plate also moves, you need a new king pin/bushings.
Carl
