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  1. #11


    g80 sorry..
    2001 Gmc Sierra 2500hd
    -All clear lights with 5000k HID -Spectre cold air intake w/ k&n cone -Cooper dicoverer ST Maxx 285/75/16 -Meyer 7.5ft poly plow E60 pump - 3500 Rear springs-Leveling kit- Backrack-LED interior lights - Pioneer headunit with Alpine type s 6.5 and Polk 4x6 and 12 inch pioneer sub with alpine vpower amp.

  2. #12


    Quote Originally Posted by quicksilver8817 View Post
    also i read somewhere that using synthetic in the differential is bad however the haynes book says to use 75w90 synthetic gear lube? .. also do i need to add an additive if i have limited slip?
    What GM says about a friction modifier in the G80..
    ****Important: Installing any friction modifier
    causes the clutch pack in the locking differential to slip and miss engagement. A fluid flush can often remove debris that is a contributor to clutch chatter. Adding friction modifier additive can cause a loss of locking differential functionality***

    What the Manufacturer of the G80 says...
    ****"From Mr. Ralph Holmquist of Eaton, the maker of the locking differential: "The maintenance schedule for the rear axle was developed by American Axle &Manufacturing and GM truck based on multiple tests. The Eaton locker does not require additional maintenance nor does it add heat to the lube. The lube will darken due to the carbon wear on the clutch surfaces, much the same as a disc brake pad & rotor. This does not damage axle components such as seals or bearings.

    However, a new axle can produce excessive temperatures (plus 350 degrees F) due to the ring & pinion breaking in that will break the lube additives down. Avoid high loads, trailer towing and high speed extended driving during the initial break in of the vehicle.

    After the break in period axle temps will level at a much lower figure. Lube changes are a good idea because the additives are replenished and contaminates such as casting sand are eliminated. The Axle is filled at the Factory with a Synthetic 75/90W GL5 rating made by Texaco under part # 2276.

    The GM Service # is 12378261. This is the only lube we have done extensive testing with to insure locker compatibility. The only negative to using one of these other lubes is an increased potential for clutch chatter. This really doesn't hurt anything and can be corrected by changing the lube. I noticed in the latest GM owners manual the term "or equivalent" when referring to the lube specification. Look for a GL5 rating on the bottle to make sure the ring & pinion, seals & bearings are protected. Limited slip additive is not needed

    "The following information outlines the type of Rear Axle lubrication utilized in GM Truck Axles.
    I. Fluid Type
    II. The 1500, 2500 and 3500 GMT 800 Trucks utilize SAE 75W-90 Synthetic Axle Lubricant. The GM part number is 12378261 and the specification is 9986115.
    Last edited by 99'HEARTBEAT; 09-05-2012 at 10:45 PM.


    5.3 l 3.73 l G80

  3. #13


    thanks for the reply.. im really set on the one afe offers however everywhere i look it is for the duramax and there is no listing for the vortec .. i think this is because it has the sight glass and it is set to factory fill level but you will be using more fluid because the cover is deeper so idk if there is a difference between the 2500hd vortec 14 bolt rear end and the duramax 14 bolt .. on the website there is a picture and mine is identical to the aa-14-11.5 diff which should fit .. i just wanna know why its not listed for the 6.0 vortec and just for the duramax?

  4. #14


    how can i identify which diff i have if the tag on the differential is gone ? help please .. i can get a deal on one but have not one clue if it will fit ..

  5. #15
    Jr. Engineer Jamm3r's Avatar
    Join Date
    Dec 2012
    Minneapolis area


    Count the bolts.
    Minneapolis area - 1997 K2500 regular cab long bed + 8.5' Western Unimount plow + modified transmission + 2nd battery + modified camper charge circuit + 1971 Cayo camper -and- 2004 4x4 Suburban 2500 8.1 + Maxbrake controller + 2nd battery + modified trailer charge circuit + Reese receiver, pulls 30' Airstream trailer

  6. #16


    Quote Originally Posted by the phantom View Post
    Ive got a "Perfect Launch" rear diff. cover made by Proform but havent installed it yet. These covers have the 2 bolts that stabilize your bearings. They also have the drain and fill plug in them and are somewhat stylish. A bit on the pricey side at around $150 for our trucks. I will give some feedback in a few weeks since mine is going to be installed along with my new gears a week from Friday.


    Proform/Specialty Auto Parts has added this aggressively designed, super lightweight Perfect Launch differential cover to its ever-growing line of GM and Ford performance parts. Less weight equals more speed, so lighten up your rearend with these Perfect Launch reinforced diff covers. They have been specifically designed to add strength to the rear housing case, which is particularly important during heavy torque situations. Each Perfect Launch cover includes two bolts to stabilize bearing main caps, two magnetic drain plugs and cover mounting bolts for your application. These covers are available for the GM 10-bolt (P/N 66668), the GM 12-bolt (P/N 69502) and the Ford 8.8-inch (P/N 69501) rearends.
    Proform/Specialty Auto Parts
    The Proform is about 1/2 the price of other diff covers. I seriously doubt that those bolts will do anything for the bearing caps, but it does have a drain plug!!!!

    Does the 66668 part fit 2013 10 bolt G80 differentials?

  7. #17


    Hey folks I think I read (maybe here) that the ribbed for additional cooling was not really true, but more for looks. I still have the original one on my truck. If I had to replace it why would I look at the ribbed vs OE? are they bigger for more oil and thus can I change the oil less frequently? Sorry not meaning to hijack... But why would the OP choose one over the other? I can understand a drain plug, magnetic... but are the Ribbs a big plus?
    Finally a signature and Avatar! I also posted some pics in the Gallery.
    2011 2500HD Crew Cab 4X4 Z71 6Liter.
    2011 Outback Travel Trailer 260FL
    So Happy to not be on the edge of GVWR Over Load!!

  8. #18
    Jr. Engineer Jamm3r's Avatar
    Join Date
    Dec 2012
    Minneapolis area


    I have the Mag-Hytec covers on the rear axle and the transmission on my 'burb. Came that way from the previous owner.

    You do get more fluid capacity which I see as a plus.

    I would be surprised to learn that the use of an aluminum housing with ribs leads to materially lower internal temperatures.

  9. #19


    i have the 14 bolt cover.. but i believe there is a 10.5 and 11.5 .. how do i know the difference?

  10. #20
    Jr. Engineer Jamm3r's Avatar
    Join Date
    Dec 2012
    Minneapolis area


    I could be mistaken but I believe that the 11.5 is full floating while the 10.5 is semi-floating.

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