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The manual on my new 04 Chev does not discuss changing the lube in the (locking) rear end. This used to be recommended at the first 3000 miles or so. Is this no longer a requirement ? Thank you
 

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I changed my front & rear diff, as well as my tcase, over to Mobil 1 at 3K. My tranny got flushed and refilled with Mobil 1 ATF at about 5K. And I run Mobil 1 oil in my engine too. Notice a pattern here?
 

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See recommended maintenance items printed by Eric under Do it yourself articles forum. Even if you don't tow, 3-5,000 the first change is good. Piece of mind if nothing else.

5000 miles

Drain and refill rear axle lube if equipped with the G-80 Eaton differential. It is only required at this interval to remove break in material.
 

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JimWilson, how do you like the Mobil 1 ATF? I have Mobil products in all other parts of my truck as well. Some have posted that the Mobil 1 in the tranny caused a temp INcrease and some slippage. I was wanting to swap over to the Syn ATF Mobil and am looking for your thoughts on the product.


Thanks for taking time to give me your thoughts!!
 

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I haven't changed mine, however I followed the manual's service intervals and checked the levels at 10k miles.. The rear was a quart low from the factory, front was spot on.
 

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SC-DMAX said:
JimWilson, how do you like the Mobil 1 ATF? I have Mobil products in all other parts of my truck as well. Some have posted that the Mobil 1 in the tranny caused a temp INcrease and some slippage. I was wanting to swap over to the Syn ATF Mobil and am looking for your thoughts on the product.
I had Amsoil in everything (engine, diffs, tcase and tranny) up until just recently. Sadly, my tranny puked out a torque converter 3000 miles ago. Now, I don't know if Amsoil had anything to do with it but when I got her back I decided to wait at least 1K and then change ALL of it over to Mobil 1.

So far everything is fine -- no problems whatsoever. I can't give you an idea about tranny temps just yet, because it hasn't gotten out of the 30's in a while around here. I can say that with the all Amsoil setup my tranny ran about 20 cooler under just about all circumstances. And I getter better mileage running all synthetic too.
 

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Discussion Starter #8
Thank you all ,


Dmaxallitech's maintenance schedule looks good to me
 

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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
 

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I finally got around to changing my rear axle fluid over the holiday. I thought nothing is too good for my new truck, so I went to my local parts dept. to buy four quarts of GM "grape" axle lube for my G-80. I had expected it to be a bit more expensive than regular mobil 1 synthetic GL-5 that I run in all my other vehicles. I was astounded when my parts guy told me the stuff is 29.00 per quart. I almost flipped out. He ended up selling it to me for 25.00 per quart. I wish I had read this post before then - I would have good ole mobil 1 in my rear diff. Oh well, live and learn...


davis091
 

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Thanks for the post you just might have saved me some money. Has anyone out there using a less expensive lube had any problems? What about the additional noise? Is it loud or is it just some clicking at low speeds?
 

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My entire truck is running M1 (front & rear diffs, tcase, tranny, engine... heck, even the grease I use is M1 synthetic). To date I haven't had a single problem with anything. And the tranny runs a bit cooler now, so that makes me happy.
 

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any one want to buy gm synth diff fluid i have tos unopened get it from warranty see when you do any thing with diff's leak rebuild and replacement. you have to bill out fluid. well gm fluid never is equal to the amount needed you knoe 2.5 qts they dont have a .5 qt so you need to bill 3 it all adds up
 

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patrick said:
any one want to buy gm synth diff fluid i have tos unopened get it from warranty see when you do any thing with diff's leak rebuild and replacement. you have to bill out fluid. well gm fluid never is equal to the amount needed you knoe 2.5 qts they dont have a .5 qt so you need to bill 3 it all adds up

Hi Patrick


I am looking for 7 qt of 90w grape juice. Send me a PM about what you have and what you need for it.


Thanks


Rich


Poorloser
 

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I had my dealer change my diffs fluids out Thursday. The Grape Juice cost more than the labor. The diffs and a tranny fluid/filter change ran me $232. High, but worth the piece of mind.
 
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