I had no problem separating the ball joint with a hammer - leaving the nut on a few threads is a good idea. If it doesn't come apart with a couple of whacks, then consider a pickle fork - you won't know until you get there. When installing the new one it is a good idea to put a small jack underneath to help things to seat and stay stationary while you put the nut on. I did this on the car rather than in a vise. I'm just telling you what I did, don't take this as necessarily the "right" way of doing it.