Rear end fluid

[dcZ71]

I have about a gallon of this in mine, very thick, quiets her down back there. 14 bolt g80 no additive

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[monstar_est87]

Heres my 10 bolt G80, I kno i need 2 clean her...

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Shes leaking a bit but ill take care of that with a new gasket wen i change the rear end fluid...

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[Sparg93]

Monstar - if you use go with RTV, make sure to get Permatex GEAR sealant...their normal "Black" stuff is not designed for synthetic fluid.

 

[monstar_est87]

Go to know... Adding to cart thanks sparg...

 

[Blue95]

I used the black with no issues when I did mine almost 50K ago

 

[KReePiN]

i used the black as well....still no issues either

 

[SAATR]

Ok, here we go. Here's the TSB originally put out on the issue:

Info - Rear Axle Lubricant Compatibility and Usage #99-04-20-001 - (06/18/1999)
Rear Axle Lubricant Compatibility and Usage
1988-99 Chevrolet and GMC C/K, G Van and P1-3 Series Models

1999 Cadillac Escalade

Built after the VIN Breakpoints (C/K) listed below:

This bulletin is being revised to add the 1999 Model Year, VIN Breakpoint information, and additional text. Please discard Corporate Bulletin Number 86-42-04 (Section 4 - Driveline/Axle).

Plant
Make
VIN Breakpoint

Arlington
Chevrolet

(Pickup)
XR703077

Arlington
Chevrolet

(Pickup)
XR703078

Arlington
Chevrolet

(Tahoe-4 Dr)
XR148860

Arlington
Cadillac

(Escalade)
XR409680

Arlington
GMC

(Pickup)
XR703184

Arlington
GMC

(Pickup)
XR703113

Arlington
GMC

(Yukon-4 Dr)
XR516469

Arlington
GMC

(Denali)
XR914788

Flint
Chevrolet

(All)
XF062378

Flint
GMC

(All)
XF062366

Janesville
Chevrolet

(All)
XJ471026

Janesville
GMC

(All)
XJ771410

Silao
Chevrolet

(Tahoe-2 Dr)
XG206200

Silao
Chevrolet

(Tahoe-4 Dr)
XG206323

Silao
GMC

(Yukon-4 Dr)
XG534060


This bulletin is being issued to inform dealers about the compatibility and usage of the new Fuel Efficient SAE 75W-90 Synthetic Axle Lubricant, GM P/N 12378261 (In Canada use P/N 10953455), with current axles, and with the non-synthetic axle lubricant, GM P/N 1052271 (In Canada use P/N 10950849), for the rear axles on the above light-duty trucks.

Testing has shown that the new synthetic lubricant will chemically attack the Room Temperature Vulcanizing (RTV) sealant. Use only the non-synthetic lubricant, P/N 1052271, in axles using RTV sealant (See 9.5 and 10.5 information below).

American Axle and Manufacturing (A.A.M.) has approved the use of the new Fuel Efficient SAE 75W-90 synthetic axle lubricant for rear axles with the following restrictions:

All 8.6 inch axles are compatible as originally built.
9.5 inch axles on vehicles built prior to mid-February 1998 are NOT compatible because RTV sealant is used on the cover pans. On vehicles built after mid-February 1998 and equipped with 9.5 inch rear axles, synthetic lubricant, P/N 12378261, can be used because the RTV was replaced with a gasket. Other mid-February changes to the 9.5 inch rear axles include a new cover pan and cover pan fasteners common to other axles.

Important
The new cover pan is not retrofittable to the housing of 9.5 inch axles on vehicles built prior to mid-February 1998. A new retrofit kit is available that will enable the use of synthetic lubricant for vehicles built after mid-February, 1998.


All 10.5 inch axles prior to March 3, 1999 are compatible if the axle shaft hub seal (RTV) is replaced with P/N 327739 gasket when changing to synthetic lubricant.
As a product improvement, this new lubricant has been released into 1999 current production C/K vehicles built after the above VIN breakpoints (Except HD3500 models which use 75W-140 synthetic lubricant, P/N 12346140).

It is recommended that synthetic lubricant be used when changing rear axle lubricant for the following reasons:

Potential fuel economy
Lower operating temperature under severe usage conditions

Important
You do not need to wash/rinse any non-synthetic lubricant from the axle cavity when changing over to a synthetic lubricant. However, you should remove debris from the magnet and the bottom of the axle cavity whenever the axle fluid is changed.
On light-duty trucks equipped with locking differentials, do NOT use a limited-slip additive.

Parts Information
P/N
Description
Quantity

327739
Gasket, Axle Shaft Seal
1

12378261

(In Canada use P/N 10953455)
Fuel Efficient SAE 75W-90 Synthetic Axle Lubricant
1

1052271

(In Canada use P/N 10950849)
Non-Synthetic Lubricant
1

12471310
Kit, 9.5 Inch Axle Cover Pan
1


Parts are currently available from GMSPO.



GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these 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 your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

Notice the date of June 1999 and the part numbers quoted. This is specifically pertaining to the use of GM RTV and GM 75W90 synthetic gear oil. THIS IS NOT A BLANKET STATEMENT PERTAINING TO ALL SYNTHETIC GEAR OILS AND ALL RTV COMPOUNDS. Gear oil formulation, including base stocks and friction modifiers (if any), vary from manufacturer to manufacturer. So do RTV formulations. The Technical Data Sheet for Permatex Ultra Black makes no mention of being incompatible with ANY lubricating oil, or of any material for that matter save gasoline. It can be found here:

http://www.devcon.com/prodfiles/pdfs/fam_tds_371.pdf

The TDS for the Gear Oil RTV Sealant says the following:

...

The product has been specially formulated to
withstand the harsh gear oil environment found in many
differentials and transfer cases that destroys normal RTV
materials. Normal RTV’s are broken down by friction modifiers
found in many gear oils and causes leaks and seepage.

...

Note that there is NO mention of the base stocks used in said oils, i.e. synthetic vs. non-synthetic. This is most likely because those friction modifiers can be added to ANY oil, synthetic or not. Due to the wide range of oils that can be labeled as synthetics (Group III, IV, or V base stocks) the word "synthetic" really gives little real world information about the chemical formulation of an oil save that at least part of it was synthesized (wholly or as a crude oil derivative).

The Permatex Gear Oil RTV IS the safest bet, no doubt, despite the large amount of anecdotal evidence (my personal experiences included) that say there should be no problems with any oil resistant Permatex sealant. The bottom line is that the best course of action would be to contact the oil's manufacturer about possible reactions between their oils and the sealants you are using, instead of relying on rumors and speculation from the internet. Do your own research and draw your own conclusions! Don't rely on mine or anybody else's!

 

[Sparg93]

Ok, here we go. Here's the TSB originally put out on the issue:

The Permatex Gear Oil RTV IS the safest bet, no doubt, despite the large amount of anecdotal evidence (my personal experiences included) that say there should be no problems with any oil resistant Permatex sealant. The bottom line is that the best course of action would be to contact the oil's manufacturer about possible reactions between their oils and the sealants you are using, instead of relying on rumors and speculation from the internet. Do your own research and draw your own conclusions! Don't rely on mine or anybody else's! [/FONT]

Totally agree with you on both fronts!!

Specific to the manufacturer and their Gear RTV, check out http://www.permatex.com/products/pr...ers/permatex-gear-oil-rtv-gasket-maker-detail Click on the TDS sheet and you will see where I'm coming from.

I've used Permatex Right Stuff for years, but now that they make a RTV more resistant to synthetics, the switch was a no brainer for me.