From another forum:
This ia a letter from Eaton, manufacturer of the G80 diff in the C3, and most all other 1/2 ton trucks (not the Quadrasteer trucks)
"Axle tolerances of the trucks are very tight. The recommended
procedure was to change lube after 500 miles of heavy towing, which is considered a break in period. This breaking period generates high heat conditions in the axle which was found to degrade the synthetic 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."
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."
From Eaton Q & A:
Automatic Locking Differential Lubricants. [Note from Michael Asmussen, Torque Control Products Division of Eaton Corp.] We recommend the following lubrications for our locking differentials:
1)Texaco 2276; Synthetic 75 W90; Gm Part # 9986115
2)Texaco 9622; Mineral based 80W90; GM Part # 9985290
3)Texaco 2080; Synthetic 75W140 (heavy duty applications); GM part # 9985991
Note - All of the above lubes are preblended with friction modifier. No additional modifiers are necessary or recommended. As far as other lubes are concerned, any standard GL 5 lube will work, but the units perform optimally with the three listed above.
[Comment from Castrol:] Thank you for contacting Castrol regarding Syntec 75W-90 GL-5 gear oil in your Volvo differentials with an Eaton Automatic Lock. You may use SYNTEC gear oil with full confidence.
[Comment from Mobil:] Mobil 1 Synthetic Gear Lubricant meets the GL-3, GL-4 and GL-5 API ratings. If the manufacturer requires the use of a GL-4 rated lubricant ONLY, then you should not use Mobil 1 Synthetic Gear Lubricant.
[ July 10, 2005, 10:25 PM: Message edited by: Bill W ]
