Differential

[Jasonsupafly]

2001 Z71 5.3... I'm wanting to take the cover off of the rear differential to clean and do a fluid change. The code in my box is GT4. It's the 3.73 gears. How would I know if I need to add the additive or not ? Im planning to run the Mobil1 synthetic fluid. Is thi s okay ? Also are the replacement gaskets at any of the autopart stores worth anything or should I go to the dealer ? Any help on this topic is greatly appreciated. Thanks in advance..

[dlstewart01]

GM did not put a limited slip in any trucks with the exception of the quadrasteer which could be optioned with a G86 limited slip. The G80 is a locking diff and no additive is needed. heres what GM says...

 

***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***

 

The G80 and the open diff take the same gear oil...75W90 GL5 rated synthetic.

[nickvrebel]

this is only a concern on truck equipped with code G80 - which is either present or absent irregardless of the code for gear ratio.

 

last I heard any diff fluid that met the spec of "GL5" would require no additive. All mobile 1 synthetic fluids meet that spec (again, I haven't messed with this in a couple years).

 

I have "read on the internet" that no additive was needed for the truck's locking differential period - I have experienced otherwise, when using a cheap fluid I had severe chatter from a G80 equipped 2000 model truck.

 

my last truck, the 2003 was a whole different scenario with the aftermarket Eaton LSD, which required it.

 

 

as for the gasket - no need to buy one. instead get some engine gasket maker (I like the black "hi temp" version) in a tube and make it yourself, just clean the old gasket off and draw around the edge and bolt back together.

[dlstewart01]

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.

[bronyaur]

The Mobile 1 with no additive will be fine in the GT4. I never use gaskets, just RTV sealant.

[tanked_darren]

Don't buy a gasket use silicone.

[dlstewart01]

I have always used a gasket. 52 years with no leaks can't be wrong.

[tanked_darren]

I have always used a gasket. 52 years with no leaks can't be wrong.

 

I haven't been alive 52 years, but I'm sure silicone has a similiar track record, plus its cheaper if your not using re-usable ones.

[Jasonsupafly]

So the GT4 is just a code for the gear size ? And I don't have the G80 ? Just trying to make sure I read this right.

[nickvrebel]

So the GT4 is just a code for the gear size ? And I don't have the G80 ? Just trying to make sure I read this right.

If code G80 does not appear in your RPO code list then it is not equipped. If the code is there then you have it.

 

GT4 is only the designator for your gear size and does not specify the presence or lack there of for the G80.

[ken1mod]

Silicone or gasket? Both work and are used in oem,

 

Ken

[Stex]

All I can find for mobil 1 is the LS...it has friction modifers for limited slip:

 

http://www.mobiloil.com/USA-English/MotorO...e_75W-90LS.aspx

 

Do they make a non-LS or will this work with the G80? Guess I can just by the Gm but at a price..

[Black02Silverado]

All I can find for mobil 1 is the LS...it has friction modifers for limited slip:

 

http://www.mobiloil.com/USA-English/MotorO...e_75W-90LS.aspx

 

Do they make a non-LS or will this work with the G80? Guess I can just by the Gm but at a price..

 

 

You can use the Mobil 1 with no problems. No sense in buying the expensive GM Grape Juice.

[Stex]

Nick, I guess you are running the Ams s-gear. Any pro&* cons on M 1, Ams gear and Gm...I think Texaco is the Gm Syn....

[Black02Silverado]

Nick, I guess you are running the Ams s-gear. Any pro&* cons on M 1, Ams gear and Gm...I think Texaco is the Gm Syn....

 

 

AMSOIL is reformulating their Severe Gear oil and making improvements to it. I think it is supposed to be available the first of the year.

 

I feel the Severe gear is a better product.

 

Mobil 1 is good and would serve you well.

 

The GM gear oil is good as well but I can't see paying that price when you can get better protection from Mobil 1 and AMSOIL.

 

If you are interested in a quote on the cost of the Severe Gear PM me your address.