i have a 98 ZR2 blazer with a auburn Sure Grip cone style limited slip rear diff and was wondering if anybody knows if the posi additive is needed for this diff? i changed the fluid when i got the truck a few months back but never put in the additive, i havent noticed any problems with noise, or getting out of mud/snow. Also if anybody knows the RPO code for posi rear end that would be helpful. thanks.

 

The Auburn cone style limited slip rear axle requires Limited-slip differential friction modifier - GM P/N 1052358 or equivalent.

G85 & G86 were both limited-slip, but GM also messed things up by using the G80 RPO code which historically was for the Gov-Loc rear diff.