Sure Grip or not

Ok a few years back i purchased a 8 3/4 from a salvage yard it has a 741 center and it came out of about a 73 or 74 Dart. I got it for $275 but heres the thing the other day i backed up about 15ft on the street just to get straight and when i gunned it both wheels spun, one a lil less then the other. When i got this rear i was thinkin it was an open carrier, what i wanna know is could this be a worn out sure grip cluthch type and how can i tell? Also shouldn't a sure grip pull both tires at all times or do u have to back up 15ft just to get it to lock?
Author: admin