Right, so below is a scan from my 1999 GM Service Manual. For the lubrication of the locking/limited slip rear axle it indicates "GL-5 80W-90 lubricant." to be used with no other explanation. This is what I have gone by, for what it is worth. (For the conventional rear axle differential, it calls for "SAE 80-W-90 GL-5", i.e. the same.)

Now, rereading my owners manual, I noticed that for the regular differential, it says to use "SAE 80W-90 Axle Lubricant (GM Part No. 1052271 or equivalent)" but for the limited slip axle it says "SAE 80W-90 Axle Lubricant; use only GM Part No. 1052271. Do not add friction modifier." (emphasis added to the word "only.") Does this mean that this lubricant is necessary for the locking differential, as in it has friction modifiers already in it but is also ok for conventional differentials? Is it necessary for locking differentials for a reason other than because it already has a friction modifier in it? Is this difference in wording important or not? I guess it could be.

Or should I go by the information in the Service Manual? I want to think the later as this is what the mechanics would read but the inconsistencies are now bugging me too.

To further confuse things, here is a link to a 2013 AC-Delco chemicals catalog: http://www.crateenginedepot.com/pdfs...calCatalog.pdf There GM 89021671 (AC-Delco 10-4052) which superseded 1052271 is described as "GL-4 (80W-90)" lubricant not a GL-5 as in the service manual. The entries for the 89021671 are on page iii and 13.

The product description for 89021671/10-4052 says the following; and note the last sentence:

"PRODUCT DESCRIPTION AND FUNCTION: A specially formulated, multi-purpose axle gear lubricant for use with limited slip and conventional type axles. It is specially designed for proper year-round lubrication and can withstand wear. Axle durability. Compatible with limited slip friction modifiers and seals/elastomers"

This makes it sound like a friction modifier could be added but perhaps has not already been added. ARGH!

Also in that catalog are lubricants only for conventional axles. If the only reason to have different lubricants was that one had to have a friction modifier than your contention would make sense. However, I have not found anything in my sources that could confirm that the only reason to have different lubricants is due to the presence of a friction modifier or not. It could be the reason but I can't be sure based on what I have read.

Have you called a GM service department to ask them what lubricant to use?

Now I have become obsessed with this. LOL

 

I believe that part of the issue is a result of confusing an Eaton Gov Loc (Locker) differential with a posi traction type performance rear end for say performance cars. The clutch plates can be different and the later does not lock up like our Blazer rear ends do. In addition I think I read somewhere that GM has used the same RPO code for both (not sure on this one).

"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."

-----------------------------------------------------

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."

George

 

Now i am confused :-)
I have spoken to 3 different suppliers of parts and that includes fluids/oil for the G80 rear locking axle. All of them told me to use SAE 80W-90 GL-5 oil with additive.
The G80 locking rear axle is a Limited Slip axle as well and it says so on page 65 in the 2000 Blazer owners manual (see the pic below)






I was sure to use SAE 80W-90 GL-5 oil and additive on the rear axle on my car but now i am starting to wonder :-) :-)

 

FWIW G80 in blazer is "Eaton Locking Differential". Note text in red below. What I don't understand is why 2000 is earliest year and why Blazer is not listed.

So it seems that adding the friction modifier can actually hurt the operation of these G80 Locking Differential rear ends.

---------------------------
#PIP4054D: Eaton Locking Differential Chatter Shudder Noise On Turns - (Jul 19, 2010)
Subject: Eaton Locking Differential Chatter Shudder Noise on Turns

Models: 2004-2007 Buick Rainier
2000-2011 Cadillac Escalade, ESV, EXT
2002-2011 Chevrolet Avalanche
2004-2011 Chevrolet Colorado
2003-2009 Chevrolet Express
2000-2011 Chevrolet Suburban, Tahoe
2000-2007 Chevrolet Silverado Classic
2007-2011 Chevrolet Silverado
2002-2009 Chevrolet Trailblazer
2004-2011 GMC Canyon
2002-2009 GMC Envoy
2000-2011 GMC Yukon, Yukon Denali, Yukon XL
2000-2007 GMC Sierra Classic
2007-2011 GMC Sierra
2003-2011 GMC Savana

Equipped With a Locking Rear Differential RPO G80

--------------------------------------------------------------------------------
This PI was superseded to update model years. Please discard PIP4054C.
--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Customers may comment on a chatter or shudder from the rear axle on vehicles equipped with an Eaton locking differential. This condition would be noticed in parking lot maneuvers, turning, or during locking differential engagement and may be more noticeable when the differential is hot. Locking differential clutch chatter may be causing this concern.

Notice: This does not apply to vehicles equipped with RPO QS4 (Quadrasteer) which is part of option package NYS. Quadrasteer vehicles use Dana axles and have a different fluid requirement.

Notice: This PI does not apply to vehicles equipped with a RPO G86 limited slip differential.

Recommendation/Instructions:
If differential clutch chatter is encountered in a vehicle equipped with an Eaton locking differential, flush, drain and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on. If the condition returns, replace the rear differential clutch plates and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on. Refer to eSI for clutch plate replacement and set up procedures.

Notice: Eaton locking differentials used in 10.5 rear axles are equipped with steel clutch plates. It is a design characteristic of these steel clutch plates to exhibit more clutch chatter than other models.

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.

Notice: On Quadrasteer equipped vehicles, simply flush the rear axle and refill with the fluid listed in SI document 793720 under the steerable application.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

 

Factory Info:

Also note difference between limited slip and locking. Limited slip used in performance cars (see below). Locking used in trucks/utility vehicles. As I understand it GM designated both as G80 so there are two cases for G80 rears.

 

So to summarize: Blazers have the Eaton Locking Differential, not the limited slip differentials (G86) and therefore we should use rear-differential lubricant that has no friction modifiers in it?

Related to this is why does GM insist on the use of the gear oil 1052271 for the Eaton locking differential but says the equivalent is fine for the standard differential?

 

 

Now I'm just going to give opinion in this thread..... I believe that GM also codes the limited slip as G80 in various vehicles - so G80 does not tell if it is locking or limited slip - only that it has a traction enhanced rear (read this on another forum but have not verified this). Nevertheless, the G80 in Blazers is the Locking Differential (not limited slip) and we should not use any posi additive in it. As far as the 1052271 vs "equivalent" gear oil..... is 1052271 the dino gear oil, and is the "equivalent" synthetic gear oil? Maybe something in synthetic is not good for the locking diff clutches but is fine if there is not clutches in a standard diff. Maybe clutch material changed over the years to tolerate synthetic in newer vehicles? Also would explain why the bulletin I posted didn't cover earlier years.

In any case, IMHO dino gear oil with no posi additive should always be safe in the G80 Locking Differential in a Blazer. It seems that trying to care too much and use synthetic/additives can cause it to not work as designed. Even miss the application of the locking mechanism under power (see the bulletin).

 

So I did a quick look to further educate myself on the different type of limited-slip/locking/non-open differentials used by GM. I found this video where the reference is made to the lockers and spring-loaded Auburn type differentials used in road cars and Blazers.

Fair warning, this guy likes to use some very colorful language but it is all good-natured. I think I helped me start to understand the differences and the confusion about the names.

 

I want full posi ! LOL.