Fluid for 2013 GM 4x4

[johnmyster]

Again ... I disagree.

You don't have to disagree. You're correct. Thanks for the correction. My understanding was incorrect for all these years, having owned several of them, including having swapped a G80 center section into my 2000 Silverado.

I don't see a spring providing static pressure on the clutches, which would be necessary for LSD action prior to lockup...unless the bevel of the spider gears serves to drive the side gears out and into the clutches. This could provide LSD bias proportionate to applied torque.

Current truck is a helical and...much preferred...but requires a FM booster for quiet operation on pavement.

 

[burbguy82]

This is the source of confusion. G80 is an option code for a limited slip. GM has used different types of limited slip device through the years on different vehicles. Some have clutches, some do not.

Every GMT G80 eaton supplied gov-bomb (Gov Lock) I've ever seen had pawls that engage the spider gears based on a rotatey spinny spring loaded governor thingy. For these, friction modifier is irrelevant. Not needed, but harmless. No clutch material to speak of. That said, I haven't handled/owned very many.

GM TSB #91-4-109 might be a good starting point.

View attachment 266399

To the OP - 75w-90 is appropriate for your vehicle. Use a quality GL5 fluid you can find at a good price. Pay no attention to "limited slip additive" markings on the package. Valvoline, Supertech, Mobil, etc.