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#2005828 - 09/02/10 02:05 PM Mixing Synthetic gear oil
palmer_df0130 Offline


Registered: 01/23/10
Posts: 24
Loc: NC
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?

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#2005843 - 09/02/10 02:17 PM Re: Mixing Synthetic gear oil [Re: palmer_df0130]
defektes Offline


Registered: 09/09/09
Posts: 3216
Loc: Hesperia, CA, USA
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.
_________________________
2002 GMC Sierra 5sp. 4.3L 145K ST3980 E-Core
Chevron Supreme 5w-30, Amsoil Synchromesh In Tranny
Valvoline SynPower 75w-90 Gear Oil In Rear

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#2005874 - 09/02/10 02:41 PM Re: Mixing Synthetic gear oil [Re: defektes]
palmer_df0130 Offline


Registered: 01/23/10
Posts: 24
Loc: NC
So would it be safe to mix or go with 3 quarts of the same brand?

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#2005909 - 09/02/10 03:04 PM Re: Mixing Synthetic gear oil [Re: palmer_df0130]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
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.

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#2005919 - 09/02/10 03:17 PM Re: Mixing Synthetic gear oil [Re: mechtech2]
palmer_df0130 Offline


Registered: 01/23/10
Posts: 24
Loc: NC
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?

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#2005925 - 09/02/10 03:20 PM Re: Mixing Synthetic gear oil [Re: palmer_df0130]
dparm Offline


Registered: 04/19/10
Posts: 12453
Loc: Chicago, IL
No, should be fine.
_________________________
2011.5 BMW M3 saloon ZCP
der stärkste buchstabe der welt
Castrol Edge Professional TWS 10w60 + Mahle OX 254D3

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#2005938 - 09/02/10 03:28 PM Re: Mixing Synthetic gear oil [Re: dparm]
palmer_df0130 Offline


Registered: 01/23/10
Posts: 24
Loc: NC
Cool! Thanks guy's for the help.

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#2005970 - 09/02/10 04:11 PM Re: Mixing Synthetic gear oil [Re: palmer_df0130]
Loobed Offline


Registered: 07/20/07
Posts: 3742
Loc: Northern California, USA


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.
_________________________
Engine: 2001 GM 5.3L LM7
Current Fill: Valvoline Synpower 5w-30 w/Pure-One PL25288 filter

I.M.N Oil Enthusiast

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#2006085 - 09/02/10 06:56 PM Re: Mixing Synthetic gear oil [Re: dparm]
dailydriver Offline


Registered: 03/14/06
Posts: 6907
Loc: Bucks County, Pa.
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 wink ).
_________________________
2000 Z28 1SC 6 speed 170K miles
Red Line 0W-40/Sustina 0W-20 (80/20 mix)
Amsoil EaO 64 filter
Synpower 75W-140/4oz. XL-3
Ravenol MTF-2

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#2006089 - 09/02/10 07:03 PM Re: Mixing Synthetic gear oil [Re: dailydriver]
LT4 Vette Offline


Registered: 09/12/04
Posts: 12195
Loc: USA
Don't some cars/trucks need a friction modifier added to the gear oil ? shrug

My old Ford needed it when I replaced the gear oil.

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#2006142 - 09/02/10 08:21 PM Re: Mixing Synthetic gear oil [Re: Loobed]
Mike_dup1 Offline


Registered: 11/17/02
Posts: 3011
Loc: USA-Michigan
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.
_________________________
2012 Sierra Denali CC 6.2L AWD
2009 Cadillac CTS4
2010 John Deere X728SE
2006 Honda Rincon 680

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#2006729 - 09/03/10 01:29 PM Re: Mixing Synthetic gear oil [Re: Mike_dup1]
dailydriver Offline


Registered: 03/14/06
Posts: 6907
Loc: Bucks County, Pa.
^^^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. wink )
_________________________
2000 Z28 1SC 6 speed 170K miles
Red Line 0W-40/Sustina 0W-20 (80/20 mix)
Amsoil EaO 64 filter
Synpower 75W-140/4oz. XL-3
Ravenol MTF-2

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#2006772 - 09/03/10 02:14 PM Re: Mixing Synthetic gear oil [Re: dailydriver]
palmer_df0130 Offline


Registered: 01/23/10
Posts: 24
Loc: NC
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.

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#2006868 - 09/03/10 04:02 PM Re: Mixing Synthetic gear oil [Re: palmer_df0130]
endeavor to persevere Offline


Registered: 04/10/05
Posts: 443
Loc: Middle Tennessee
In 1999 the G80 locking diff was an option on the trucks. Starting in 2004 the G80 was part of the Z71 off road package. and also a stand alone option.


Edited by endeavor to persevere (09/03/10 04:08 PM)
_________________________








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#2006903 - 09/03/10 04:43 PM Re: Mixing Synthetic gear oil [Re: Loobed]
endeavor to persevere Offline


Registered: 04/10/05
Posts: 443
Loc: Middle Tennessee
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.


Edited by endeavor to persevere (09/03/10 04:54 PM)
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