My '55 1st has a serious shake between 50 and 55. Its nice and smooth up to 50 and nice as smooth past 55.
New radials on new wheels less than 10,000 miles ago. New shackles and pins this past weekend. With the exception of the drag link, all the steering seems tight. The kingpins are good and tight. Wheels bearings were all replaced a couple years ago.
I feel it in the body and the doors shake bad enough I either speed up or slow down. I also feel it in the steering, but have never decided if its because the wheels are shaking, or if the body is shaking the steering column.
When I was a kid my dad had a Ford f-250 4x4 that would do the same thing, and replacing the parts I'd associate with the kingpens fixed it. He owned that thing long enought that I replaced them a couple times.
