make sure you tap out the locking "dent" as well, the outer ring of the nut is normally dented in to keep the nut from spinning off. You'd be suprised, but that little bit can keep the nut from comming off at all.

If you need extra leverage, use a short piece of pipe on the breaker bar, works wonders. Heating the nut with a torch helps a bunch too.

Electric impacts can be very helpful if you do a good amount of your own repair work, they are much larger than most air impacts but get the job done nicely if you dont have a large compressor to support an air impact.

Also, when re-installing everything, do NOT tighten the nut with an impact.