I read all the other threads on getting the old rusty ones off, but I'm having trouble installing the new ones. How do I tighten the top lock nut without the internal shaft spinning? Do I use an allen wrench in the top? Thanks.

 

you can probably use a vise grip on the top or something to hold the stud

 

x2 ^, thats what I had to do, or sometimes you can get a wrench in there to hold it.

On mine, the wrench was to big to fit in there and still be a big enough size wrench to fit on the stud and crank the nut down.

I think I used craftsman locking pliers on mine.

 

my new Bilsteins have a spot for an allen wrench at the top of the threaded stud. I used a block of wood to prevent it from spinning and tightened it with a wrench. All is well.

 

I use vice grips when at home. Sometimes an impact gun is enough to tighten them without them spinning.