Get both rear wheels off and the car supported in neutral you will soon see the difference between drag caused by the lsd and brake bind, you should get a fairly easy turn of the disc at it's outer edge of about 1", certainly by hand when grabbing the bell part of the disc, although infrequent use can make these VERY tight due to rust etc, mine took around 50 miles before all traces of rust were gone and they were easy to turn the 1" or so.
tabetha