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Thread: Eaton's Recommendations on Locking Rear Diff Service

  1. #1
    Join Date
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    Arrow

    "GM introduced the new body style in 1998. At the same time they upgraded
    the differential and changed to a synthetic lube. The G80 is specifically
    designed to give ultimate performance with this lube, and the lube contains
    special additives that help reduce slip stick that occurs between the
    clutches. the GM synthetic lube typically runs about 100+ degrees cooler
    than mineral base lube, which is better if you do allot of towing or heavy
    hauling. I would recommend that you stay with the GM synthetic, not Mobil 1.
    If you don't tow or haul you could use the pre 1998 mineral lube without
    degrading performance of the differential. this would be a cheaper option
    but require more lube changes. "

    "Axle tolerances of the 1/2 ton trucks are very tight. The recommended
    procedure was to change lube after 500 miles of heavy towing, which would is
    considered a break in period. This breaking period generates high heat
    conditions in the axle which was found to degrade the synthetic beyond the
    point of mineral lube. After the 500 mile lube change, the axle is broke
    in and does not generate the high heat. If you use GM synthetic after the
    break-in period, it can be considered "lube for life", although some say to
    change it at 40,000 - 50,000 mile intervals."

    "If you don't tow, don't worry about the oil change as it a waste of money."


    "If your truck is pre 1998 or the old style, it comes with mineral lube. IN
    that case you need to stay with mineral because the seals are designed to
    work with it. If you changed from mineral to synthetic you'll cause your
    seals to swell and eventually leak. It's ok to go from synthetic to
    mineral because you won't cause swelling. many of your stop leak
    chemicals effect seals in this manner, resulting in a short term fix but a
    long term problem."
    TxDoc's Photos
    Member #5547

  2. #2
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    Post

    TxDoc,

    I got this straight off the Eaton Webpage FAQ

    http://www.torquecontrol.eaton.com/prod6.htm

    "What type of lubricant and limited slip additive should I use with my newly purchased Eaton Limited Slip Differential?

    Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford)."

    I was getting ready to put Mobil 1 in, since it is API-GL5. Other than Eaton's above recommendation and since GM itself is going against this recommendation, why do you not recommend Mobil 1?

    If you got your info about their using synthetics from Eaton, are they not also contradicting themselves?

    Joe
    02 GMC 2500HD D/A EC LB SLT
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  3. #3
    mark45678 Guest

    Thumbs up

    I have been using redline inthe rear end since 600 mile! except I am useing 90/140 weight. no chatter while cornering and locks up tight when it needs to !!! and its about 10 dollars a QT.....

  4. #4
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    Apr 2001
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    Exclamation

    Allison Jettester

    Both statements are correct. The Eaton limited slip rear end does require mineral based oil and additive. Synthetic is too slippery and the clutches don't get enough friction to engage and balance torque.

    The [Eaton] G80 in the HD's and 3500's is not a limited slip rear end, by traditional terms. It is referred to as the "Gov-Loc" rear end. It does have carbon clutches, but they are engaged by a governor. Using mineral based oil and an additive in this rear end will very likely greatly reduce its useful life. The use of only mineral based oil, without an additive, wouldn't be nearly as bad. The design did not include the use of the additive, which, among other things, contains mostly acid. The acid prevents the oil in traditional limited slip rear ends from glazing to the clutch surfaces, which causes the chatter by preventing lubrication. Synthetic oil will not glaze to the clutches like mineral based oil, and over lubricates the clutches. The G80 in our HD and 3500 trucks do not maintain constant friction like the older limited slip models. It only engages the friction clutches when there is a given amount of differential wheel speed. This has many advantages. Namely the reduction of heat in the rear end, and greatly reduced wear of the friction clutches, as they are not under constant load. See for yourself. Jack up the rear end, both wheels. It will act like an open diff. when one wheel is spinned. Notice no felt friction (or there shouldn't be, anyway).

    Why would anyone want to deny his rear end of the best lubricant currently available?

    Hope this helps explain it.

    Additionally, synthetic oil should be used in the front end of a 4 x 4. Although it is not under the same load, or used as often as the rear end, they are usually neglected by rare service. Mineral based oil will absorb water (from submersion or condensation) and decompose over time (Yes, mineral oils decompose, after all, it is organic. That is why old oil gets that rank smell). Synthetic oils have an indefinite static life. Cheers (Boy! This should stir the pot, not that it is intended to)
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  5. #5
    Join Date
    Dec 2001
    Location
    Eugene, OR
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    Post

    So...

    In simpler terms, does our G80 rear diff require the limited slip additive or not? Changing my fluid this weekend with the $20 quart GM stuff. Thanks in advance

    Kyle

  6. #6
    Join Date
    Aug 2001
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    St. Louis, MO
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    Post

    No, our axles don't need anything but good synthetic GL-5 rated oil. No additives.

    After long investigation the bottom line is that the only GM spec. is for GL-5 synthetic.

  7. #7
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    Nov 2000
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    Post

    The post I made was a quote directly from Eaton's reply about what is okay and not okay for use in conjuction with the locking rear end option.

    Back in November, I received the following:
    "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 75w90 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.
    TxDoc's Photos
    Member #5547

  8. #8
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    Post

    More good information! Thanks TxDoc. First time I'd ever heard that about going from mineral to synthetic causing seal problems. Very interesting.
    GM needs to pour some magic in their lube bottles if they're going to continue to ask crazy money for it. I'm betting my rear end (no pun intended) that Mobil 1 will work just fine
    02 Chevrolet 2500HD LT Pewter/Tan, 4x4 Crew Cab, Allison and 403 <b>CUBES \'O DIESEL JOY</b>!

  9. #9
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    Apr 2002
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    SF Bay Area
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    Post

    Anyone see a problem with running Redline 80W140 in the G80 rear diff? I've got a case of this stuff.

    Gary
    Gary<br /><br />2002 Chevy 3500HD, Duramax, ZF-6, Crew Cab, LongBed<br /><a href=\"http://www.teamSMR.com\" target=\"_blank\">www.teamSMR.com</a>

  10. #10
    Maverick Guest

    Question

    Is the Amsoil synthetic gear lube GL5 rated?

  11. #11
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    Post

    Maverick:
    Yes at least the 75W140 Amsoil Syn is rated API GL-5, that what I run in mine. I think Eaton recommends this weight for heavy towing.
    Ed
    GMC 3500 D/A 4x4, SLT<br />Running Boards, Lucerix Mirrors, gauges,CB,Street Pilot III w/outside antenna, Jordan Brake Controller,U.S.Gear Exhaust Brake,Amsoil Air and Dual Remote Oil Filter,Rhino Bed Liner, Mud Flaps.<p><a href=\"http://www.picturetrail.com/Edmac\" target=\"_blank\">Pictures</a>

  12. #12
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    See my previous post.

    posted 04-12-2002 11:28 AM
    --------------------------------------------------------------------------------
    Just hit 1500 miles and have chosen to change engine oil and rear end lube. Get the junk out of it early. Purchased my own gm filter and Rotella dino oil (4gal @ $5.89). Had the local quick oil change location do the service for me. They charged me $39.99 for the rear end lube (Pennzoil 75-90w synthetic) and changed my oil and filter with no additional charge. They even primed the oil filter! Although I am new to diesels, I do not believe that any new noises have occurred.

    Yes it is GL-5. Cut and past link below for more info.

    http://www.pennzoil.com/TechData/pds...lusSuperEW.pdf

    [ 04-18-2002: Message edited by: konacat ]

    [ 04-18-2002: Message edited by: konacat ]</p>
    2001 2500HD GMC Duramax/Allison Summit White CC/LB<br />Rhino, Reese 5th wheel hitch<br />2002 Cougar 279EFS<br />1973 CR250M Elsinore

  13. #13
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    Jan 2001
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    Fort Worth
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    Post

    I changed my diff at 500 miles. filled with Castrol 75/90 gl-5 full synthetic. have 18000 miles now no problems.
    2001 2500HD D-Max/Allison C.C. 4x4 L.T. X.M. radio, turn over ball,Prodigy brake controller Westin side bars,285/75/16 BFG A/T, more.

  14. #14
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    DMAXMAVERICK (AND /OR OTHERS)--I just purchased Mobil-1 75W-90--it might have a modifier added. Will this be OK for the G80 locker or should I return it? The product sheet states it exceeds requirements for ALL car and truck rear axles, and reduces chatter in limited slips. It states it is suitable for all applications requiring API service GL-5. Please respond. Thank you.

    [ 04-20-2002: Message edited by: gdblake ]</p>
    2002 Crew Cab, LS, SB, 2500HD Duramax/Allison, 3.73 LS, Trailering pkg, loaded. White/tan, Buckets

  15. #15
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    gdblake

    Mobil 1 is a high quality lube and should work well with no worries. This, of course, is my opinion. I have not conducted any testing of Mobil 1 gear lube. The additives refered to with most synthetics is not the same as is needed to add to dino oil in a limited slip application.

  16. #16
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    Thanks so much, DmaxMaverick--I've really been hangin', hoping for an answer. Anxious to change the diff. Appreciate your response. Had a call into Mobil, but they were closed for the weekend. Best regards!
    2002 Crew Cab, LS, SB, 2500HD Duramax/Allison, 3.73 LS, Trailering pkg, loaded. White/tan, Buckets

  17. #17
    Join Date
    Dec 2001
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    Lexington Park, Md
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    Lightbulb

    DmaxMaverick,

    I've been in Rota, Spain for the past few weeks and didn't see your post answering my post above. I had the mind set that the whole question and answer page on the Eaton website I quoted referred to the G80 Locker. They changed the subject to limited-slip and I didn't catch it (I should have since that is the kind of thing I always look for when reviewing government specs!).
    Thanks for straightening me out. That's one thing good about this forum--if you are in error, someone with sharp eyes will catch it.

    Anyway, you are correct (as far as I know) that any GL-5 rated synthetic gear oil should be ok in the G80 Eaton's "Gov-Loc" LOCKER. Now that I have bought both Redline (with additive) and Mobil 1 I am going to have to make a decision on which to use.

    Also, I did jack up the rear and there was a LOT of friction in the rear when I turned one wheel. I could hear a lot of noise coming from it. I do believe the opposing wheel did turn in the opposite direction like an open diff, but am going to do this again to be sure.

    Thanks again,
    Joe
    02 GMC 2500HD D/A EC LB SLT
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  18. #18
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    Post

    TTT
    2003 GMC 3500 SLE, D/A, EC, LB, 2WD, White/Pewter, DeeZee boards, 5th wheel

  19. #19
    Join Date
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    port orchard,wa.
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    Post

    Am using Almasol 607 from Lube Engineers Inc in a Mag-Hytec rear-end cover.

    Towin' like a mutha. No heat/wheel drive issues.

    w/t
    2001 black truck, powerful engine,<br />pneumatic tires (4), <br />2-way glass, fully-upholstered inside seating, 12volt dc lighting, one-man steering wheel,interior heating, wipers, aftermarket 8-track...more.

  20. #20
    Join Date
    Sep 2002
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    Post

    Two different fluid to choose from: 75w-90 & 75w-140. Can someone please explain the difference, what each number represent? I'm not too familar with how the fluids are rated. Thanks.
    2002 Chevy Silverado 2500HD<br />Ext. Cab SB 4x4 LS<br />6.0L/HD Auto.

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