Power Steering Issue. Opinions wanted

I noticed, while driving yesterday, that my steering seemed to develop a dead spot in it. Meaning I have to rotate the wheel a good 8 inches or so in the opposite direction before the steering becomes positive again. Almost like something is loose and the wheel is not turning the linkage until it catches. This is on a 72 Dart that has been completely restored. I have only been able to quickly scan it when I got home due to it being late and dark. Any suggestions to expedite my trouble shooting? Thanks folks