Check for a limited-slip differential
A lot of old-timers went with Pontiac or Oldsmobile rear ends because of their beef over 1955-64 Chevy and Ford rear ends. How can a person tell if a Pontiac or Olds rear end is Positraction or open? In the case of a 1957-64 Chevy a large “P” is embossed in the carrier. Was there some similar way to check a Pontiac or Olds rear?
One way to determine whether a particular rear axle is or isn’t a limited-slip is to take the cover off or pull the carrier out and look at it.
If the rear is in a vehicle, the standard test to determine whether it’s a limited slip or open unit is to raise the drive wheels up in the air, put the transmission into neutral, and manually turn one of the wheels. If the opposite wheel spins in the opposite direction then the differential is not a limited-slip unit. If the opposite wheel spins in the same direction as the one you’re turning manually then the differential is a limited-slip.