i plan on replacing the u-joints, they're hfs springs and extended barbell shackles. they didn't give me any advice. although their site is kinda informative if you are the researching type. basically what you're saying is it wouldn't hurt to just put the shims in there?
I was wondering if the manufacture of the spring suggested that you use them in any of their sales literature concerning your specific application.
I also stated that I had not ever ran into needing them in any of the lifts that I have installed, or vehicles that I have worked on over the years, in the rear axle, specifically. I am aware that there are people that have needed to use them, and that it has cured their vibrations. I was also trying to say that vibration issues can be a sign of bad u-joints, along with bearings in gear boxes or differentials.