Chevy G80 Differential Oil

[RichardSenn]

Okay simple question probably.

I have the G80 rear end in my Chevy Silverado and Tahoe. I need to change the gear oil and I've read numerous GM bulletins saying not to add the friction modifer because the G80 in my truck is a locker not a limited slip like the G80 in cars. Apparently there is a lot of confusion on this but I know it says not to add the modifier.

My question is this. I was going to use Mobil 1 75W-90 but it says it has friction modifiers in it already for limited slip differentials, but then it goes on to say if you need more modifiers you can purchase OEM modifier additive. Is it okay to use in my G80? The Mobil 1 statement has me a little confused on the has modifiers but you can add more?

 

[johnachak]

That certainly would foul me up too! Mine needs the additive so I guess except for being out like an additional $15 or so I'm lucky????

 

[cchase]

Mobil 1 75w90 will work fine.

 

[RichardSenn]

Originally Posted By: johnachak
That certainly would foul me up too! Mine needs the additive so I guess except for being out like an additional $15 or so I'm lucky????


I know I'm a little confused. I also just checked out Royal Purple and it says the same thing.

 

[4Kings]

If you do alot of towing you might consider running a 75W140. I run Mobil 1 75W140 in my 2500HD.

 

[229]

Your locker is made by Eaton and called an Gov-Loc.

"Originally Posted by General Motors

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 10950849).

The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.

VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
© Copyright General Motors Corporation. All Rights Reserved."

We call the factory oil purple juice and it smells like candy and costs almost $30/qt..

If you are out of warranty and want to reduce the price you can use an GL-5 w/o the FM. Ford revised their synthetic to 85W140 and it will make your gears last longer with a small hit to fuel economy.

 

[RichardSenn]

Originally Posted By: 229


We call the factory oil purple juice and it smells like candy and costs almost $30/qt..

If you are out of warranty and want to reduce the price you can use an GL-5 w/o the FM. Ford revised their synthetic to 85W140 and it will make your gears last longer with a small hit to fuel economy.


229,

That's the same bulletin I keep reading. I guess I'll just buy the factory fill "purple juice". I'm still confused on whether Mobil 1 is considered as having the additive or not since it mentions possibly adding OEM additive.

Quote:
Mobil 1 Synthetic Gear Lube LS 75W-90 contains special friction modifiers designed for limited slip-type differentials. In most applications, the addition of special LS (limited slip) additives is not required. For axles requiring the highest level of limited-slip performance, OEM specific LS additives can be added to this fluid.

 

[justinf89]

I'm about to change mine out with amsoil svg after researching this issue also. I'm not going to add any fm either. It was changed at the dealers around 30k but I'm not sure if it was done real early like the bulletin says. Just another thing to think about.

 

[RichardSenn]

Originally Posted By: justinf89
I'm about to change mine out with amsoil svg after researching this issue also. I'm not going to add any fm either. It was changed at the dealers around 30k but I'm not sure if it was done real early like the bulletin says. Just another thing to think about.


Yes, I might just find and Amsoil dealer and get the severe gear oil 75w-90.

This is a good read. It was put out by amsoil but appears to be pretty unbiased.
http://www.amsoil.com/lit/g2457.pdf

 

[4Kings]

Royal Purple MaxGear gets positive reviews.

 

[NHHEMI]

I have had 2 Silverados with the G80 and I ran RP MaxGear 75W-90 in both with no problems. 99% of the guys on the Chevy truck sites run either RP, Amsoil, or M1 with absolutely no issues from the added FM. Just don't add any extra and you will be perfectly fine.

DO NOT waste your money on the GM Grape Juice. It is way over priced and nothing special. Buy M1, RP, Amsoil, etc... for 1/2 the price.

 

[NHHEMI]

Originally Posted By: RichardSenn

This is a good read. It was put out by amsoil but appears to be pretty unbiased.
http://www.amsoil.com/lit/g2457.pdf


The white papers unbiased?

Thanks, I needed that.

 

[Pablo]

Originally Posted By: RichardSenn
Originally Posted By: justinf89
I'm about to change mine out with amsoil svg after researching this issue also. I'm not going to add any fm either. It was changed at the dealers around 30k but I'm not sure if it was done real early like the bulletin says. Just another thing to think about.


Yes, I might just find and Amsoil dealer and get the severe gear oil 75w-90.

This is a good read. It was put out by amsoil but appears to be pretty unbiased.
http://www.amsoil.com/lit/g2457.pdf


Please choose an Amsoil dealer sponsor from THIS website. Our proceeds support BITOG as the other sponsors do. If you are going to recommend an Amsoil dealer, BITOG is the place to come.

 

[endeavor to persevere]

What Eaton 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 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.

 

[Whitewolf]

Your information is now out of date. The 9986115 fluid is being replaced by another fluid designated 9986285 for improved oxidative stability and low temperature. The 998 numbers are however GM internal numbers not what you would find in the average dealership.