Pivot shaft problems

That's a self prevailing lock nut. It's "squished" on that outside to make the nut a "force fit" on the control arm pin so that it will not back off. That's what's causing the pin to spin and the nut not to tighten up, just like @mopowers up there ^^^^^ described. You must over come that by turning the nut faster than the pin and the only way to do that is with an impact gun. I much prefer air.

And yeah, I already told you about that @72bluNblu dork. He's a legend genius for sure. Great asset to the site.