G80 Locker Codes

[01BlackZ71]

Is G80 the same designation for a rear locker on a 1997 2-door Tahoe?  My 2001 Z71 has the G80 code, and (go figure) it has the locker.  My friend wants to know if his 97 Tahoe has a locker.  It doesn't have the G80 code, or the Z71 code for that matter.  He just bought it, and will be mad if it doesn't have the locker.  But, we thought that maybe since his Tahoe is an older generation that the code on it might be different.  Anybody know?

[TxDoc]

Just some info on when the G80 came out and when you should service it and how:

 

 

 

 

Here is some info Eaton sent me in the past:

 

"GM introduced the new body style in 1998. At the same time they upgraded

the differential and changed to a synthetic lube. The G80 is specifically

designed to give ultimate performance with this lube, and the lube contains

special additives that help reduce slip stick that occurs between the

clutches. the GM synthetic lube typically runs about 100+ degrees cooler

than mineral base lube, which is better if you do allot of towing or heavy

hauling. I would recommend that you stay with the GM synthetic, not Mobil 1.

If you don't tow or haul you could use the pre 1998 mineral lube without

degrading performance of the differential. this would be a cheaper option

but require more lube changes. "

"Axle tolerances of the 1/2 ton trucks are very tight. The recommended

procedure was to change lube after 500 miles of heavy towing, which would is

considered a break in period. This breaking period generates high heat

conditions in the axle which was found to degrade the synthetic beyond the

point of mineral lube. After the 500 mile lube change, the axle is broke

in and does not generate the high heat. If you use GM synthetic after the

break-in period, it can be considered "lube for life", although some say to

change it at 40,000 - 50,000 mile intervals."

 

"If you don't tow, don't worry about the oil change as it a waste of money."

 

 

"If your truck is pre 1998 or the old style, it comes with mineral lube. IN

that case you need to stay with mineral because the seals are designed to

work with it. If you changed from mineral to synthetic you'll cause your

seals to swell and eventually leak. It's ok to go from synthetic to

mineral because you won't cause swelling. many of your stop leak

chemicals effect seals in this manner, resulting in a short term fix but a

long term problem."

 

Back in November, I received the following:

"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.

¨ Note: the recommended lube for HD trailer towing is a 75W-140 Synthetic Gear lube, part number 12346140.

III. Inspection/Change Frequency

¨ The 1500 and 2500 GM Trucks recommend rear axle fluid level checks every 7500 miles. Fluid should be added as needed.

¨ Under heavy duty trailer towing conditions the lube should be changed after the first 500 miles of towing. This is due to the extreme heat generated on break-in of the hypoid gear set."

 

 

 

 And, thanks to Turbo Al for this info:

 

Written by "Shawn Spickler" of Off-Road.com

 

The greatest damage to a new gear set results when it has been run for ten minutes or more during the first 500 miles and the oil is very hot. Any heavy use or overloading while the oil is extremely hot will cause it to break down and allow irreversible damage to the ring & pinion. In order to make them run cooler and quieter, new gears are lapped at the factory. However, they are not lapped under the same pressures that driving creates. These loads generated while driving, force any microscopic high spots on the gear teeth back into the surface of the metal. This is called "work hardening". Work hardening is similar to forging in the way that it compresses the metal molecules into a very compact and hard formation. This can only be accomplished if the metal surfaces are lubricated and the gear temperature stays cool enough that the molecular structure does not change. If the temperature of the metal gets hot enough to change the molecular structure, it will soften the surface instead of hardening it. This may seem like a balancing act but it all happens easily & passively as long as the oil keeps the gear cool while it is breaking in. Some of the synthetic oils on the market today can help a gear set live longer. Theses oils will continue to lubricate at temperatures where many crude oils break down. Even with synthetic oils, you should still follow the procedure for

BREAKING IN A NEW GEAR SET:

After driving the first 15 to 20 miles it is best to stop and let the differential cool before proceeding. Keep the vehicle at speeds below 60 mph for the first 100 miles. You should put at least 500 miles on the new gear set before heavy use or towing. During the first 45 miles of towing it helps to go about 15 miles at a time before stopping to let the differential cool for 15 minutes before continuing. This is necessary because not all of the gear tooth is making contact until it is heavily loaded. When towing, the teeth flex to contact completely, and cause the previously unloaded portion of the teeth to touch and work harden. All of this may seem like paranoia, but it is very easy to damage the ring & pinion by overloading before the teeth are broken in. It is a good idea to change the gear oil after the first 500 miles in order to remove any metal particles or phosphorus coating that has come from the new gear set. This is cheap insurance and a good time to discover any problems before they grow to disastrous proportions.

Again thankyou Shawn Spickler

[Z71IN']

The 1997 Z71 I'm buying has the G80 code in the glove box... so it sounds like he doesn't have it.

[ClipperSkipper]

The 1997 Z71 I'm buying has the G80 code in the glove box... so it sounds like he doesn't have it.

True it should be on the build sheet.

 

Have a great one!

[Dihappy]

Thats some GREAT information.

 

For those of you (like me) that have an Auburn Diff, heres some info:

 

The Auburn Gear limited-slip differential design has been extensively tested with high quality non-synthetic 80W90 hypoid oils treated with GM or Ford friction additives.

(3 oz. of additive will treat 1 quart of oil).

 

To avoid differential clutch chatter (noise) and for optimum

performance, use the oil and additive described above.

 

Use of other additive and oil types may

cause differential clutch chatter.

 

Ford Part Number: C8A219B546A

GM Part Number: 1052358

[GnatGoSplat]

How many of GM part # 12378261 should I buy if I'm going to change my rear axle lube?

[Z71IN']

If you check your owner's manual it will tell you the capacities,or your dealer should be able to tell you.