Rear end fluid??

[Dragon_90_K5]

Hey Guys,
I just got a set of axles for my K5 with 4:10's and an Eaton Posi. I wanna get the Gear oil and just thought I would ask you what is popular. I was thinking about the lucas Oil fluid. Anyone useing it? Any information is helpfull.
Chris

 

[Hogback Fabrication]

First you need to be sure of which Eaton "posi" you have. What axle do you have?

Eaton makes the notorious gov-lok (G80 code) which was a factory option for just about every GM truck made from the 70's on. Eaton also makes a clutch type limited slip for 10 and 12 bolt axles.

I would bet you have a gov-lok, which requires no special fluid. I would recommend 80W90.

If you have a clutch type limited slip then you need a friction modifier (an additive that goes in with the gear oil).

You can either:

a)take the diff cover off and post a picture here showing which limited slip/locker you have

b)jack up the rear (with the t-case in 2WD) and try to spin one tire. If you can spin one tire (and the other goes the opposite direction) you have either a gov-lok or an open differential. If you can't spin the tire at all, you have either a posi or a locker.

 

[Dragon_90_K5]

Hey man. Thanks. I have the clutch type. I thought I needed the additive But couldnt remember. Thanks