Rear end gear weight?

[HemiDog]

How would you determine what weight gear lube to use in the rear end?   
I am running a 4.10, Detroit Locker in a Dana 60.

[Chryco Psycho]

Typiaclly use 80-90 but for better milage use 75-90 synthetic

[rallyechall]

Does the synthetic work with the LS additive? Is there another additive you need to purchase?

[ShelbyDogg]

Herb McCandless brought this up on the power Tour.  He said do not use synthetic gear lube with the clutch type posi units.  It is too slick and will penetrate the clutches.  Only use regular gear lube, then add the Mopar posi additive.

[HemiDog]

Thanks a lot guys!