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Old 03-23-2010, 01:13 PM   #11
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Sorry....forgot to add something. It's normal for the diff to get too hot to touch. However, and those who have experienced this can verify, when gear oil starts to burn, it smells really, really bad. It does not smell like 'regular' burning's got it's own nasty smell.


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Old 03-27-2010, 06:27 AM   #12
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I got out my owners manual and I still have the window sticker
from when it was new.
The owners manual says use GM part # blah blah....
I'd rather use aftermarket synthetic.
The window sticker says I have a "locking rear axle".

I know it's not the kind that people who go off roading have
that literally locks into a solid axle.
So what is it??? I think it's got clutches.

My real question is this-- If I drain and refill it with Royal Purple
synthetic 75w90 do I still need to add the K & W Posi trac additive?
I guess I'll give the folks at Royal Purple gear oil tech line a call....

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Old 03-27-2010, 06:48 AM   #13
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it's kind of the best of both worlds...I call it a have an "open" rear until there's wheel spin then the centrifical mechanism locks and it becomes a posi..yes there are clutches. This way you don't get the chattering around corners like the old posi's did
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Old 03-27-2010, 06:48 AM   #14
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Never mind-- I found the answer to the additive at the Royal Purple
FAQ for gear oil--

"Max-Gear is recommended for use in truck, motor home / RV, and automotive front or rear differentials, manual transmissions, and lower gear units of marine engines that specify use of an API GL-5 or GL-4 fluid. All viscosities of Max-Gear are formulated with hypoid friction modifiers necessary for use in clutch or cone type differentials. No additional additives are necessary."
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Old 03-27-2010, 06:49 AM   #15
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Thank you!!
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Old 03-30-2010, 01:02 PM   #16
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I have been using royal purple throughout my Trailblazer SS drive train for the past 50,000 km except for the transmission since they did not have anything rated for my transmission. I did some research on the products before I switched and found the info positive.

They advertise lower coefficient of friction which equates to a decrease in oil temperatures (how much I don't know), less wear, better thermal wear and breakdown of the oil, higher boil off temperatures, longer intervals between oil changes (oil filter every 4000 km) and better cold start properties. I am definitely going to check out my rear differential after a drive on the freeway and see how warm it is.

Over all I am happy with the fluids. One thing I also did was change out my transfer case fluid to the same fluid I use in my engine which is the royal purple 15w-40 oil instead of the fluid recommended by GM. Typical transfer case fluid can boil off just like transmission fluid and that's why your levels go down after some time. Check out the article for reasoning behind this. My dad has been a heavy duty mechanic for 50 years and swears by that info. I even use that oil in my 1300w generator and it seems to run a tick quieter then when I had conventional oil in it. I personally think anything with 5w in its specification should be left to oil up your hairdo for that slick look.

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Old 03-30-2010, 01:32 PM   #17
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Originally Posted by TravelSoftballDad View Post
"What got me thinking about this is some months back a poster here
said the "pumpkin" had gone out in his Chevy Suburban.
I don't remember if he said anything about synthetic or not."

That was me ;-(

Synthetic came OEM in that diff from Chevy...and it burned up good. Following the warranty repair service, I actually drained the new replacement oil and went to AMSOIL Synth Gear Oil after doing a bunch of research. I love it ! I learned a lot from that whole ordeal.

I added a Mag-Hytec diff cover (holds more oil, has magnetic dipstick, and a drain hole) and strongly recommend them to others. Since going to AMSOIL, I check the color and levels quarterly. To date (well over a year), the AMSOIL gear oil is still golden colored and is working like a charm.

To be honest, since that pumpkin nightmare and my AMSOIL trial(s), I have switched both vehicles over completely to AMSOIL. I guess I would be considered an AMSOIL Kool-Aid drinker, but I've tried several products and am sold completely.

Some testing of gear oils :

Hope that helps !!

I run Amsoil in both diffs and the transfer case on our 2008 2500 Ram Megacab so far so good. Also ran it in our 04 quadcab 4x4 that had 180,000 on it when we traded it in and the guy that bought it said he had never driven a new truck that felt any tighter. Mind you we are blessed with -30 to -40's in the winter here.

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Old 04-15-2010, 07:09 PM   #18
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GM trucks have had synthetic gear oil from the factory sinse 1998. All GM trucks with the G80 RPO code have a locking diff. No truck from GM is equiped with a limited slip diff with the exception of the Quadrasteer, which had a G86 limited slip.

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 75W-90 GL5 (P/N 12378261). 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.
Part Number Description ----------- ------------------ 12678261 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
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.
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Old 04-16-2010, 08:59 AM   #19
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g80 locker

That was great! Thanks for that. The youtube video I mean.

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