1991 GMC Sierra Differential oil?

[countrykid]

Hey there, I just picked up a 1991 GMC sierra 1500 and I wanted to change the differential gear oil. My big problem is I'm not sure what kind of gear oil to put in it. The other problem is that it's a 14 bolt (3500) rear end on a 1500 truck. The manual calls for SAE-80W 90 GL-5 for standard axles, and SAE-80W 90 for locking axles. I'm pretty sure mine is a locking rear axle because it's 4 wheel drive and that would make sense, but the axles tag for identification was rotted off. I'm really looking for some help on what to put in it. If you know a lot about this and you need a picture of the axle itself, i got the cover off so email me [email protected] and you can tell me what kind of axle i have and what kind of gear oil to put in it. Thanks a lot.

 

[Evert]

I would use the one recommended for the limited slip. It will work fine and if it is limited slip and you use the non limited slip oil It could cause problems with the clutches.