Mixing Synthetic gear oil

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I have a 1 quart and a half of Pennzoil Synthetic 75W-90 GL-5 gear oil and am having a hard time finding more. I wanna change out the rear differential fluid in my 99 Silverado with it, but all I can find around here in Jacksonville, NC is Mobil 1 synthetic, Super Tech Full Synthetic, and Valvoline Dura Blend. Would it be ok to mix what I have with Mobil 1 or the Super Tech or should I buy 3 new quarts of the same brand?
 
I wouldnt use ST gear oil, they failed viscosity tests like a year ago, causing their product to be pulled from shelves in CA. Not enough to damage your car but enough to put me off the product, go with the M1, or look for Full Valvoline Synpower.
 
It would have to be safe, as the designations and ratings are the same - they have to be compatible.

But we change our diff fluid so rarely that I would get the same product in there. The edge in smartness and probability for best results goes this way.
So you lose $8 over 3 years time.
 
I will probably go with Mobil 1. What's the deal with the LS(Limited Slip) on the Mobil 1 bottles? I know my truck does not need any limited slip additives, will that screw anything up in the diff?
 
I tried the Valvoline synthetic 75w-90 gear oil in my 2001 Sierra with G-80 rear end. It did not like it and chattered. I changed it a few times with more Valvoline, but it was always the same result. I tried Mobil-1 and it was better, but I still got a few clunks. The best I found was Amsoil Severe Gear 75w-90. After about 50,000 miles on the Amsoil I started to get a little chatter. I put in some of the GM limited slip fluid and the chatter went away.
 
Originally Posted By: dparm
No, should be fine.


+1

If anything it would help quiet down the ring & pinion (if they were making any noise to begin with
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).
 
You are not supposed to use limited slip additive in GM truck G80's. Trucks use a mechanical locking rear differential and the use of the limited slip additive is not recommended and advised against by GM.

Limited slip G80 are installed in cars, the GM trucks use a Eaton Locking rear differential.

clunking is normal with a mechanical locking differential when it engages.

http://www.youtube.com/watch?v=q-rQTHMVAuw
http://www.youtube.com/watch?v=-sw9DwurQAs

fyi

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION)
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 . 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:

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.
 
^^^In which cars exactly did GM istall the G80??!

Also, did palmer's '99 Silverado come standard with the G80?

(If so, then YES, I take back my recommendation that the M1 LS gear oil is OK.
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)
 
I believe it did come standard. I will have to look at the codes in the glove box and decipher it by going to a GM/Chevy forum.
 
Originally Posted By: Loobed


I tried the Valvoline synthetic 75w-90 gear oil in my 2001 Sierra with G-80 rear end. It did not like it and chattered. I changed it a few times with more Valvoline, but it was always the same result. I tried Mobil-1 and it was better, but I still got a few clunks. The best I found was Amsoil Severe Gear 75w-90. After about 50,000 miles on the Amsoil I started to get a little chatter. I put in some of the GM limited slip fluid and the chatter went away.



As what was stated earlier...

Heres what GM says about the truck G80

***Important: Installing any friction modifier causes the clutch pack in the locking differential to slip and miss engagement. A fluid flush can often remove debris that is a contributor to clutch chatter. Adding friction modifier additive can cause a loss of locking differential functionality***

heres what the manufacturer of the G80 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.
 
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In which cars exactly did GM istall the G80??!

All rear wheel drive cars it was an extra cost option ONLY. Some performance cars got it as part of a certain option pkg, e.g. Camaro SS, Firebird Trans Am etc. Never put into FWD cars.


I have the AMSOIL Severe Gear 75W-90 in my 2009 CTS4 with G80 limited slip differential. Also in the front of same car, its AWD. And in my 2010 GMC with G80 locking differential, both front and rear.


fyi...........
The same G80 option code is used for both but the truck G80 is NEVER a limited slip. For some all wheel drive trucks that use a limited slip they have a different option code for it (G86 if I recall). This is my 5th GMC with G80 and every one has been changed to AMSOIL severe gear 75W-90. I have never experienced any noise or chatter in mine and I never used any additives as I knew not to but when I had dealer change my fluid for me, they would insist I put it in and I had to argue with a few to not do it and stand there watching them change it to make sure they did not do behind my back.
 
But Amsoil severe gear has LSD additive in it already.... you're breaking the rules.

BTW, who cares what GM says anyway.
 
Originally Posted By: Mike_dup1
Quote:
In which cars exactly did GM istall the G80??!

All rear wheel drive cars it was an extra cost option ONLY. Some performance cars got it as part of a certain option pkg, e.g. Camaro SS, Firebird Trans Am etc.


So GM used that code for the Torsen T2 helical/worm gear limited slip that came standard in my car??

(The 4th gen f bodies NEVER had a locker type diff as a factory option, nor standard. Unless there was a top secret program I've never heard anything about?)
 
email from GM Training on the question of the rear diff on the Camaro is a locker since the RPO code is "G80" like the trucks G80 locker:

"Thank you for your question concerning the all new 2010 Chevrolet Camaro. You asked, “Is the limited slip differential a g80 locker? the rpo order code in autobook shows "g80" as the code for the limited slip rear differential.”

Although the order code is G80, the Camaro has a Limited Slip Differential. It is not a locking differential like those found on our trucks.




Thanks again for your inquiry. Good luck and good selling!

The Camaro Marketing Team


There you have it, right from the horses mouth!!!
 
Quote:
So GM used that code for the Torsen T2 helical/worm gear limited slip that came standard in my car??

(The 4th gen f bodies NEVER had a locker type diff as a factory option, nor standard. Unless there was a top secret program I've never heard anything about?)


I had a 2002 Trans Am WS6 with the Thorsen LSD and the build sheet does say G80. Note the day this car was built 9-11-01
LS1build.jpg
 
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