Fluid Change Questions (Diffs + Transfer case)

Discussion in 'GM Powertrain' started by ejj, Aug 29, 2009.

  1. ejj

    ejj New Member

    My truck as 80k miles, and I don't know the maintenance history. I would like to change all the fluids in the differentials and transfer case. I have a few questions:

    * My manual says that the front diff uses 80w-90 for "Four-Wheel Drive" models, and 75w-90 for "All Wheel drive" models. Since mine is electronically selectable (Auto, 2H, 4H, 4L), do I assume that's the Four-Wheel drive model?
    * What is the approx capacity of each diff? I can't find this listed anywhere, and I'm not sure how much fluid I'll need for each.

    Transfer case:
    * Again, Auto vs. Four-Wheel. For Four-Wheel drive, the listed fluid is AUTO-TRAK II. Is this available at any part store, or a GM only part?
    * My Haynes manual lists close to a dozen Transfer Case models. How do I identify mine? Is there a tag on the case?

  2. Z07

    Z07 Member

    Look for a fluid service tag on the fill plugs. It is a stamped piece of aluminum about 1.5 inches long. It will list the fluid needed.

    Your RPO codes on your option sticker will tell you what diffs and t-case you have too.

    If you can't find a tag and can't decode the RPO then post pics of the diffs and t-case.

    Always remove the fill plug BEFORE you remove the drain because if the drain plug comes out freely and the fill plug is seized then you have a vehicle that can no longer move under its own power until the fill plug is sorted out.

    I follow the recommendations from Dana/Spicer reguarding the use of LSD additive. Some don't use it and have no ill affects some are not so lucky.
    Last edited: Aug 29, 2009
  3. ejj

    ejj New Member

    Couldn't locate a tag on the rear diff, but that doesn't have options. The Transfer case is a model #246, which uses the GM AUTO-TRAK II. Do I have to get that through the dealer. According to the Haynes manual, I need 2 quarts.

    Couldn't locate a tag on the front diff either, but based on the transfer case, I assume I need 80w-90. Can the dealer confirm this for me? I need to stop there for parts anyways...

    I hadn't heard of LSD additives used in the diffs...should they be?

    Any input on the capacity of both diffs?
  4. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Unless you have an aftermarket clutch type LS, you don't need any kind of LS additive. The factory diffs (open or G80) don't need the friction modifier additive.

    80/90 gear lube should be fine for the diffs

    You do need the blue ATII fluid for the transfer case. I haven't yet seen available aftermarket, so I think you still need to get it from the dealer (be careful asking aftermarket places. I had some try to tell me that AT II and DEX III are close enough).

    And I will second removing the fill plugs first. There's isn't much worse than getting the fluid drained only to find out that you can't fill it. I don't know if they changed it by 2005, but the fill plug on my '98 NV246 takes a 5/16" square head driver which I had a hard time buying off the shelf. Ended up buying a 1/4"Fx3/8"M adapter and grinding down the 3/8" to 5/16".
  5. ejj

    ejj New Member

    I picked up 4 quarts of ATII at the dealer. Is that enough for a drain and fill?

    Anyone have any input on how much gear oil is needed for each diff?

  6. 1st Synthetics

    1st Synthetics Epic Member 5+ Years 1000 Posts

    I would say 1.5 quarts in the front and 2.75 in the rear, but that is a guess.
  7. Browntowns20s

    Browntowns20s Rockstar

    just take it in to a service shop, we do both difs and the transfer case for 250-
  8. ejj

    ejj New Member

    Now that's no fun. I prefer to do it myself.
  9. grimreapersshadow

    grimreapersshadow Rockstar 100 Posts

    your rear should take about 2 1/2 quarts and the front maby 2 quarts best way to know is fill em to the plug and it dribbles out a bit then your done
  10. 1st Synthetics

    1st Synthetics Epic Member 5+ Years 1000 Posts

    Your transfer case should only be 2 quarts of Auto-Trak II.

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