According to my RPO. I'm supposed to have a 3.42 LSD in my 1985 Iroc. However, the guys that work on her said it's an "open" differential. I tried the old jack the axle up routine and spun the wheels. First, we spun them and they were spinning opposite each other. Then I held my side and we tried to spin the other wheel and with this scenario I was able to stop the other wheel from spinning. I know the best thing to do is just open her up and look at the carrier. In lieu of this, any thoughts as to what I really have here?

 

They do fail especially those stock Auburn units. Pop it open and look. Replace it with an Eaton or Yukon unit.

 

There is a very good chance some time in the last 37 years someone swapped the rear end with another to fix an issue. Pull the cover and see what you got.

 

My 1984 T/A was born with a peg leg. This spring I am going to install a Yukon Gear. Not cheap but my '72 Buick GS had a posi that I installed and so will my T/A.

 

There are some types of gear driven limited slips that will act like an open differential when the tires are loaded one way, and then the gears will lock up when the tires are loaded a different way.