FYI- Keep in mind that the Rubi may require the addition of a limited slip addititve (friction modifier) to the diff oil. Check with your dealer or manual.

 

I just did my rear as I had a little drip after wheeling this weekend. I opted for Royal Purple

 

Lucas oil 75-90 front and rear

 

The Rubi does not need the limited slip additive. It has the e-locker. Non-rubi models equipped with the D44 limited slip need the friction modifier. Agree that if you don't know check with your dealer or manual.

 

Most synthetics don't require friction modifier. Read what the bottle says.

 

I, too, am using the Valvoline 80-90. But, that's because the locker in my front axle specifically says to NOT use synthetic with it. Unless you've got an Auburn locker, you should be fine with synthetics.

 

At 45K, however, I'd recommend going ahead and pulling the diffy cover after draining. Have some brake cleaner handy (at least a full can, maybe two) and clean up and inspect the gears for anything obviously wrong. You can use RTV gasket sealer when reinstalling the covers, but I'd recommend LubeLockers. Worth the price the next time you pull the covers.

 

X2..........

 

unless the axle has a limited slip, u dont need friction modifier.... and pretty much all syn gear oils like RP, amsoil, etc already have the modifier added to it. i run amsoil 75w90 syn front and rear, and there 5w20 earl.