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Rear Differential Fluid Change.

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by stchman, Jun 10, 2013.

  1. steved

    steved Former Member


    The only thing I could see happening is if it was overfull it would aerate and foam...

    However, the way a differential lubrication system works is that the ring gear slings the lubricant up into the front of the housing to flood the pinion bearings. So if its a little over filled, its not going to know the difference (think about running on a side hill, up or down a steep hill, etc...the level is always changing anyway.
  2. j cat

    j cat Rockstar 3 Years 1000 Posts

    I never seen a diff go bad from too much fluid. some say the seals could get damaged from pressure build up.

    I know that if the vehicle is not level you can put 4.5 QTS in it . or put in 1 qt too little. if the front end is high you can overfill very easy.
  3. stchman

    stchman Active Member 1 Year 1000 Posts

    I was under the impression that differentials have some kind of venting system on them so too much pressure cannot happen.
  4. steved

    steved Former Member

    Yes, the venting would prevent pressure buildup.

    FWIW, I ran the 11.50AAM in my Dodge (same thing under a Duramax) with an ORU cover that placed the fill port 1.5 inches higher...I ran with the fluid that much high, in an 85w140 blend for 150k miles, then switched to a 75w140 for another 50k. I never had a dribble.

    The AAMs are a very good axle...
  5. j cat

    j cat Rockstar 3 Years 1000 Posts

    the venting hose can over time get plugged up. when I had my frame crossmember replaced they crushed this hose / did not route it properly. I caught this the next day when I dropped the fuel tank and rustproofed the frame and the crossmembers. even with the diff being properly filled had I not caught this I would have had seal damage/leaks. this fluid expands alot when heating under use.

    my front diff was factory filled too high and it was coming out the over flow .
  6. shibby2oo8

    shibby2oo8 Member 2 Years 100 Posts

    I allways fill them til they drip out, never had a prob. Also rear ends get pretty toasty and the vent tube is important. Ever notice a salt truck covered in slush but the pumpkin is bone dry?
  7. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    I have not been able to find the correct volume of fluid; however, the level should be between 1/2" below the hole, to the bottom of the hole (truck level).
    In other words, if checking and the level is no lower than 1/2" below the hole, the level is good. If filling, or topping up, the fluid should be added until it drips out of the fill hole.
  8. steved

    steved Former Member

    From the 2012 OM:

    To get an accurate reading, the
    vehicle should be on a level
    surface.

    For all 4.3 L, 4.8 L and 5.3 L
    1500 Series applications, the
    proper level is 1.0mm to
    19.0mm (0.04 in to 0.7 in)
    below the bottom of the fill hole,
    located on the rear axle.
    Add only enough fluid to reach
    the proper level.

    For all 6.0 L and 6.2 L
    1500 Series applications, the
    proper level is from 15mm to
    40mm (0.6 in to 1.6 in) below
    the bottom of the fill plug hole,
    located on the rear axle.
    Add only enough fluid to reach
    the proper level.

    For all 6.0 L 2500HD Series
    applications, the proper level is
    from 0mm to 13mm (0 to 0.5 in)
    below the bottom of the fill plug
    hole, located on the rear axle.
    Add only enough fluid to reach
    the proper level.

    For all 6.6 L Duramax Diesel
    2500HD Series applications and
    all 3500 Series applications,
    the proper level is from 17mm
    to 21mm (0.6 in to 0.8 in) below
    the bottom of the fill plug hole,
    located on the rear axle.
    Add only enough fluid to reach
    the proper level.


    Interesting enough:

    All axle assemblies are filled by
    volume of fluid during production.
    They are not filled to reach a certain
    level. When checking the fluid level
    on any axle, variations in the
    readings can be caused by factory
    fill differences between the minimum
    and the maximum fluid volume.
  9. stchman

    stchman Active Member 1 Year 1000 Posts

    So all in all it sounds like just fill the diff until it comes running out the fill hole.

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