Axle Lubricants??
 

What oil is recommended in the rear end with the G80 gizmo in the rear end? I think it is synthetic.

GM has their version of course. It sounds like it's about $28/quart. Mobil 1 and AMSOIL both have a 75W-90 made for limited slip. They probably run a 1/3 the GM price. Can get you exact numbers on AMSOIL if interested.

^^^^ i agree. gm sells their own label. 32 oz runs you about $25 a bottle. p/n is 89021677. as long as it's a synthetic ur fine. no additive needed for the locker. and unless ur towing you really don't need to change it more than every 50k.

There are new 75W110 fluids coming out. They are basically HD 75W90, but don't suck your mileage like a 75W140. With these trucks putting down more torque than ever, the added protection of the 110 is what I run and recommend. Earlier this year, it was Ford who actually pushed API for a new 75W110 gear lube category. Ford was having trouble getting their diesel truck differentials to make it to the end of their warranty on 75W90, so they are now running 75W110. AMSOIL makes a 110 grade fluid, not sure who else does at this point. More will be coming to market during the year.

Info here: https://www.amsoil.com/storefront/svt.aspx

-Chuck

I only have 23k on my truck but i guess it is never too early to switch to a better than OEM lubricant. I like the idea of the 75/110 wt gear lube, i may wait till i clear the 36k mile mark for warranty reasons.

There's no warranty problem but whatever you are comforatable with. The first change is recommended anywhere from 15-20k to rid of the initial wear particles from new parts, especially if doing a bit of towing, but you'll have no problems waiting. It's the most neglected fluid but you rarely see if fail since most come synethic from the factory now.

I changed my front and rear diff fluid at I think it was 6K and I used the Gm brand (Grape juice, for its grape scent). It is a synthetic and needs to be a synthetic because of the locking diff. You will need six quarts(it only takes five and a half). I know a lot of guy that are running Mobil 1 synthetic and like it very well and it is cheaper.

I use Ams Oil gear lube in the front and back. I have a Mag Hytech diff cover on the back and would not do it any other way.

Get that stock crap out ASAP. 9 times out of 10....the fluid level is not correct from the factory and the fluid is milky looking.........so do yourself a favor and change it ASAP!

Will do BOBO.... and welcome to the site!!!

Yes, welome to DM bobo.