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  1. #21


    And I just checked Amsoils site about what fluid to use just as a secondary and they said ATF also for the xfer case

  2. #22

    Default No limitit slip additive on g80 locking diff!!!!!

    Quote Originally Posted by vms4evr View Post
    This will be fine front and rear. The synthetic diff fluid will work over a big temperature range and actually simulate more than 75w-90 range. It works fine. That is what I'm running. In the rear diff with limited slip there is an additive that you need if you run dino gear oil. Mobil 1 Synthetic also says add it. As noted it helps with the clutch packs in the posi unit. You'll find it with the diff fluid at Napa and Autozone (that I know of) for about $8. It's in a tube and the stuff looks blue. If you use RP or RedLine synthetic diff fluid then you don't need the additive.

    An easy to tell if you need additive. Swap out with the new synthetic fluid. Go drive the truck in a parking lot in slow tight circles both left and right. This packs the fluid into all the spots in the diff. If you hear any noise from the diff then you need the limited slip additive. Or just throw it in. Worst case it is a waste of $8. It won't hurt anything if your diff doesn't need it.

    The only weird fluid you need from the dealer is the stuff in the transfer case. That is also some weird blue looking stuff that looks like tranny fluid. It's about $20 a bottle and you need 2 bottles if I remember right.

    Changing those fluids is part of your 50K maintenance work.
    Yes actually if you add the limided slip additive you can lose use of the locking part of G80 locking rear diff. I even have the shop manuals and i looked it up to be sure and it says plain as day DO NOT ADD limited slip additive on locking diff. the lubricant makes the locking mechanisim and clutches too slippery to lock up. I hope this helps i just didnt want anyone to mess up their diffiental by adding that stuff.

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