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Discussion Starter #1
Our thanks go to TxDoc for the following:



G80

from Eaton:
"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 broken
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."


And this,
"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.
¨ Note: the recommended lube for HD trailer towing is a 75W-140 Synthetic Gear lube, part number 12346140.
III. Inspection/Change Frequency
¨ The 1500 and 2500 GM Trucks recommend rear axle fluid level checks every 7500 miles. Fluid should be added as needed.
¨ Under heavy duty trailer towing conditions the lube should be changed after the first 500 miles of towing. This is due to the extreme heat generated on break-in of the hypoid gear set." <!-- Signature -->
 

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Quote "¨ Note: the recommended lube for HD trailer towing is a 75W-140 Synthetic Gear lube, part number 12346140."


Questions:


1). How do they define HD trailering? Pulling 8K, 10K, 12k, 15K? Pulling these loads 10%, 25%, 50%, or 100% of the time?


2). What is the 75W140 change frequency? As with motor oil, the wider the viscosity span, the harder this is on the polymers, and the shorter the oil life. Does this apply to synthetics?


3). Will the 75W140 lower my MPG as compared with the 75W90?


I pull a 10K 5ver 5k miles per year, and drive about 12K unloaded. What weight should I use? Will the 75W90 cause premature wear?Thanks for any input.
 

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Also would be nice to know the Texaco part number for the 75-140 Synthic. If we can find that on the shelf, would probably be cheaper than the GM bottle and same quality/properties.
 

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Discussion Starter #5
I believe they mean if you plan on pulling loads a lot, go with the 75-140. I don't think they can get much more specific than that and it's not critical if you do use 75-140 and do not tow.

The second question I cannot answer.

Yes heavier lubes create more hydro-drag than lighter lubes. I doubt if it's anything really significant once it's warmed up. The 75-140 range is purposely designed to handle the extremes and remain stable. Being synthetic only adds to it's ability to handle the extremes
 

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Did a Quick search on Texaco part number 2276 and found the Texaco Part number for the Synthetic 75W140 they supply GM for the locking differential. Will find out today if it can be bought at part stores.


Texaco 2080; Synthetic 75W140 (heavy duty applications); GM part # 9985991
Edited by: srode
 

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I have been trying to locate the Texaco #2080 (GM 998591) . Texaco has teamed up with Chevron I guess which has changed the numbers. I would like to know if anyone has found this 2080.


The Dealer parts man, racing buff, was talking with me about this. The GM number for the 2276 was 30 dollars and some change per quart. The 9985991 (2080) was only 25. I am sure the Texaco would be in the area of 12 dollars a quart.


I have been also looking at the Amsoil# 2000. Any opinions on this stuff?
 

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Not me, I called and looked at quite a few places. Let us know if you do find it somewhere.
 

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I'm using the Amsoil series 2000 75W-90 in my HD2500 dmax in limited slip rear with no additive. Smoother in acceleration from stop around in town street corners than oem by far. sells for $9.20 a qt. retail.
 

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I found out today that the 2080 by Texaco has change hands to Chevron/Texaco and then to shell where it has been discontinued.. They only have their (Shell) 75-95 Spirex line for the GL5 coding. I am having a hrad time believing this stuff has disappeared.
 

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Have a hard time believing it will disappear, what would GM do for the lube? Probably disappeared from all but GM Dealers.
 

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This is the reply that I got from Texaco about the 2276 and 2080 Differential oil. I guesss this says it all.








Further to your enquiry about the above product.


This is a specialist product that that is manufactured on behalf of GM and as such is not available to the general public under the Texaco brand. My suggestion would be to purchase the product through your local GM dealer.


Thank you for your interest.



Regards,


Alan C Outhwaite, Manager Customer Support.


ChevronTexaco Global Lubricants
43-45 The Promenade
Cheltenham
Gloucestershire
GL50 1LE
UK
Tel: + 44 (0)1242 266706 Fax: +44 (0)1242 266710 Mobile: +44 (0)7968 030762
 

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In reference to the rear axle:"If you don't tow, don't worry about the oil change as it a waste of money."
Somewhere in a post here from HOOT i read this quote from Eaton.I'm trying to learn as much as possible so i can take care of my baby.My rear axle developed a gasket leak after 16000 miles and was serviced under warranty by the dealer.and that included a complete fluid change(their w/o # for the fluid was 10953455?? and new gasket.I DO NOT TOW and the most weight i have ever had on was about 1000.lb.No excessive speed and i usually run on highway at 2000 RPM.CAn someone give me an expert opinion on whether or not i fall into Eaton's claim of being LUBED FOR LIFE.I do wanna take care of my truck but don;t want to get fanatical about it.


I got 60000 miles on her now and as stated before i am gearing up for a cross country trip.I will be checking the levels front and rear and am thinking i may only have to top up???


All advice/replies greatly appreciated.
 

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Not to ask a stupid question but why would you not just replace it with Amsoil or another synthetic that is a LOT cheaper than the $20+/qt?
 

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bigdog said:
Not to ask a stupid question but why would you not just replace it with Amsoil or another synthetic that is a LOT cheaper than the $20+/qt?




That is exactly what I did!









Kevin
 

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Hi All. Well I have 2572 miles on the New Truck,(2004 Chevy 2500HD). I decided to change the Oil in the rear end..Guess what! two quarts came out..I added 3 3/4 quarts of Mobil 1 synthetic. I called the Dealer


I have to call back Monday.. Is it normal they short fill the rear end? I love my truck.. Do I trust GM Dealers maint..The Jury is still out on that one.. If You really love your truck,learn to check stuff


Yourself


Edited by: marsguy
 

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I have the GM stuff in both the front and rear but when it comes time to change them will go with Amsoil probably. I'd like to actually change all the fluids to synthetic in the next few thousand miles if I can find a place that will flush the allison.
 

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Ah that is GREAT info Hoot. Thank you.


Oh and just a note of personal exerience. I changed over to a mineral based lube. GL5 rated 75-90w. I have absolutly NO clutch chatter at all.


I asked the question of why we couldn't run mineral based oils and the only reply I got was "Cuz Chevy Said So." So being the Jeeper that I am...I said F that poor excuse for a answer and put in the mineral type. ofcoarse I only have about 300 miles on the new oil but I don't have any chatter and the letter you provided from Eaton proves that it is all good in thier opinion.


I do tow but not alot and it is at most 6k worth of Jeep and Trailer. Thank you Hoot for thinking outside the box.
 
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