Yes Martin, we are in general agreement, I saw an issue that could be discussed beyond the usual "look in your repair manual" type questions on this site.
I did not have any particular vehicle in mind when I started this discussion, certainly not a truck. I guess I was thinking in terms of the '33 Plymouth I am working on which has parallel leaf springs and a 5-1/2" dropped tubular axle from Butch's Rod Shop. These axles do not have spring pads pre-mounted, so welding them in place after assembly is required, so obviously welding other brackets on is not a problem. Most Rods only have about 3" of upward travel and about 6" total and assuming a shaft angle of about 30 degrees, this would be around 1" total sliding at the joint (more or less). I was thinking that a splined joint would have a good 6" or more of overlap which should be pently to prevent any binding. Rocking the rack back and forth for whatever reason, all that would really do is slide the joint back and forth as designed, I should expect. As far as suspension breaking, the axle would bottom out on the frame, so I don't really see where thats much different from the normal travel, even if the axle pulls back some on one side, there would be enough overlap in the joint to deal with it.
As far as the factory issue goes, this would seem to me to be irrelevant as the axle era doesn't overlap with the rack era. And as far as trucks go, I don't recall ever seeing one with a rack anyway, regardless of suspension type. (as far as I know).
