I have an 199 Blazer ZR2 and i need to replace the oil on the rear G80 locking axle, Limited Slip.<br />In the owners Manual it says the following:<br />Axle lubricant, use only GM part number 1052271. Do not add friction modifier.<br />This is a Limited Slip diff and i have always used GL-4 oil usually and additive on my 1964 Corvette Sport Coupe.<br /><br />Some say that i should use synthetic 80W-90 oil and no additive. Or is the best to use mineral based GL-5 and additive?<br />I read that somechange on the rear diff came in 1998 on GM cars<br /><br />I did a search for 1999 S10 with G80 locking diff on Summits homepage and came up with SAE 80W-90 gear lube and rear axle friction modifier.<br /><br />But as i said it says NOT TO USE ANY FRICTION MODIFIER in the Owners Manual<br /><br />Any here that knows what kind of oil to use on the G80 locking diff on my 1999 Blazer ZR2?<br /><br />I have almost double posted this question on the forum here now so sorry for that but i have reserved a car lift to change the rear diff cover and oil tomorrow

 

For my 1999 LT with the G80 rear diff I've used regular Valvoline 80W-90 (pn VV832) with no extra additives.

My owners manual says to use "SAE 80W-90 Axle Lubricant; use only GM Part No. 1052271. Do not add friction modifier."

 

I just did a search and found this site where it says soemthing about the recomended GM 1052271 fluid:
https://www.autozone.com/repairguide...00c152800a7b83

 

Here is a clue from the link above:

Locking Axle
Always use GM Rear Axle Fluid No. 1052271 or equivalent SAE 80W-90 GL5 lubricant. Check with your owners manual or parts supplier, on a few earlier models covered by this guide it may be necessary to add 4 ounces of GM Fluid No. 1052358 (limit-slip additive) before refilling. BUT GM SPECIFICALLY WARNS AGAINST using limited slip additive on 1996 locking differentials and does not mention its use for many of the late-model vehicles covered by this guide.

It would look like the recommendations changed in about 96

 

 

The Saint: if you REALLY want to be worry free about whether to use an additive or not, you could trade me the open diff from my '02 for your 'ole G80.
Then you could just use standard lube and never have to worry about it.
Sound like a plan???..............LOL.......

I doubt I ever find a G80.....

 

I have searched the forum about using additive or not. Please read the link below because it says that the GM part number of differential oil have already additive in the bottle and that you need to add friction modifier if you buy oil without additive

Read the link below and specially the part about: Lubricant requirements …
https://www.dieselplace.com/forum/76...conumdrum.html

 

This is from page 7-48 of my 1999 Blazer Owners Manual (with some extra notes I added for the transfer case fluid for the 4-button transfer case)

Note that for the standard and G80 differential, it calls for the same gear oil; i.e. regular gear oil for both front and back, with or without the G80 option.

 

christine_208. I totally agree what it says in the owners manual about the G80 locking diff. It says on the G80 locking diff to use GM 1052271 fluid. From what i have understood the GM 1052271 fluid comes with friction modifier.
You just dont have to add the extra little bottle.

I am not sure about this since so many says not to use and many says to use friction modifier/additive

From what i understand the GM 1052271 fluid for the G80 locking diff have been replaced by GM 89021671 fluid
From what i understand after doing some search is that the GM part number for the rear axle fluids already contains/have the friction modifier/additive added .
So if you add more friction modifier to the original GM fluid that already have modifier in it there will be to much friction modifier in the oil and this is bad for your rear axle/car and that is why GM have written "Do not add friction modifier" in the owners manual.

Can it be that the rear axle oil you use already contains the modifier?

So if you buy axel fluid that does not have any friction modifier/additive at all you will have to add it yourself

I cant say this for sure if this is correct

In the link from the 2001-2010 Chevy and GMC Truck Forums in my previous post under "Lubricant requirements " they say the following:
"They are motivated to sell you their GM branded products, but that is not what is necessary. What is needed is a GL-5 lube with some friction modifier, and nothing more"

Below is the link to the 2001-2010 Chevy and GMC Truck Forum where they talk about this
https://www.dieselplace.com/forum/76...conumdrum.html

 

Now you got me really curious.

I looked at earlier year owners manuals and they say the same thing as mine does, 1993 and 1995. Hmmm. When I get home I'll have to check the GM service manual that I have.