What would anyone recommend for rear diff juice for a 1 ton dually?

jimbo

 

i run the amsoil 75-90 extreme duty oil. love it the diff runs cooler with that than the dino oil

 

i run royal purple 75-140 or 90 (cant remember) synthetic gear lube. it already has the friction modifier in it too if you got a ls rear.

 

75-90 is what the manual says.....

 

I just changed mine. I went with the Amsoil 75-90 extreme duty. I didn't use any friction modifier and my LS is still smooth as silk. I would go with the Amsoil.

 

I wonder why the manual changed, given the relative few differences between the OBS and NBS trucks. The 99+ service manual cals for synthetic 75w-140. I currently run the Amsoil in mine, but it's getting a bit chattery of late. It's almost due a fluid change so I'll probably go with the Red Line heavy shcockproof, or Royal Purple this next go around.

The 75w-90 is easier to find if that has any bearing on your desicion....nobody local carries the -140.