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What kind of diff do I have?

differentials

Re: What kind of diff do I have?

Postby WingNut [OP] » Mar 01 2011, 4:32am

jreagan wrote:I'm almost certain that the G80 is indeed an Eaton locker. I had the rear diff fluid changed and there was no friction modifier added. I've always assumed that GM's RPO description was just off. There are real limited slips diffs in GM passenger cars, etc. (ie, clutch plates, etc.) but I've always believed the G80 is an Eaton locker (and seems to be just that on my Silverado).

I've looked at the Eaton site and vendors who sell Eaton diffs. Nowhere does Eaton or the vendors call the Eaton mechanical locker a G80. I think the Eaton mechanical locker has picked up the G80 badge because og the GM RPO assignment. I don't know if the Eaton mech lockers were offered in 2004. So G80 in that year may heve meant the lim/slip diff.
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Re: What kind of diff do I have?

Postby 2003Z71 » Mar 01 2011, 4:57am

I've done a little research and found this on Eatons site "The Eaton mechanical locking differentials were the first to be offered as an option to pickup drivers and today it is known around the world simply by the GM option code G80. This automatic unit, available as standard and optional equipment for rear drive and 4-wheel drive vehicles, makes traction problems a thing of the past."
That said, I guess you can call the G80 a "modified" locker as a true locking diff will have bad street manners and hop, pop and bang around corners. That's why drag racers like them, they lock both axles solid with NO slip. From the GM 2003 Service Manual,The G80 locking differential uses multi-disc clutch packs and a speed sensitive engagement mechanism that will lock both wheels together if 1 wheel spins excessively during SLOW vehicle operation. At vehcile speed above 20 MPH the latching bracket overcomes a spring preload and swings away from the flyweights. At this speed the diff is designed not to lock since added traction is generally not needed.
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Re: What kind of diff do I have?

Postby Z15 » Mar 01 2011, 4:57am

Once and for all, G80 in a truck is a mechanical locking differential made by Eaton and exclusive to GM trucks. Limited slip differentials are normally installed in rear wheel drive cars like the Cadillac CTS-V, Camaro and Corvette.

Btw - Both carry the G80 option code.

The Eaton locker in the trucks goes back to at least 1988 as I have a service bulletin that mentions it and it have quoted it below.

From a Cadillac Service Bulletin
Models: 2003-2010 Cadillac CTS, Sport Wagon (Including V-Series and Export)
2004-2009 Cadillac SRX (Including Export)
2005-2010 Cadillac STS (Including V-Series and Export)
Equipped with Limited Slip Differential (RPO G80)


From a truck service bulletin
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.




Btw - I have both G80's, in the 2010 GMC and in the 2009 CTS4 wish it was a V
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Re: What kind of diff do I have?

Postby WingNut [OP] » Mar 01 2011, 7:08am

Z15 wrote:Once and for all, G80 in a truck is a mechanical locking differential made by Eaton and exclusive to GM trucks. Limited slip differentials are normally installed in rear wheel drive cars like the Cadillac CTS-V, Camaro and Corvette.

Got it Mike,

Earlier poster said my VIN was decoded as a G80 (lim slip). I'm going to get a second opinion on my VIN. If a dealer says my VIN has the G80, then I'll consider the issue settled.
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Re: What kind of diff do I have?

Postby Z15 » Mar 01 2011, 12:36pm

I was not jumping on you but trying to correct misinformation. There are often arguments over this in forums where some insist its a limited slip. I have even encountered some GM techs that do not know there is a difference, especially if they are not skilled in differentials. Believe me, I had to stop them when installing AMSOIL in my 2004 GMC because they were going to install an additive. I observed the install tech at the parts counter getting a bottle of additive and I stopped him and that po'd him off. That's the GM dealer and a tech with nearly 20 yrs of experience who was giving me the hard time.

The axle is not coded in the VIN BUT a GM can run a "build out" of any vehicle using the VIN. Ask them for a paper copy of that, don't take their word.

Just fyi - These new trucks I had were always ordered with the G80 locker
1987 Silverado regcab (my last 4x2)
1989 Silverado regcab
1992 Silverado Z71 Ecab
1996 Silverado Z71 ecab
1999 GMC Sierra Z71 ecab
2001 GMC Sierra Z71 ecab <---waited months to get this truck due to G80 on constraint
2004 GMC Sierra Z71 ecab
2008 GMC Sierra Z71 ecab
2010 GMC Sierra Z71 ecab

These cars had the G80 limited slip
2002 Trans Am WS6 LS1
2005 Cadillac CTS
2009 Cadillac CTS4

This pic below is from a 2003 GMC brochure. I had a 2003 GMC Sierra SLT Ext Cab Z71.
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Re: What kind of diff do I have?

Postby Z15 » Mar 01 2011, 1:10pm

More info on the G80 straight from the GM Order/Reference Guide proving there are two different G80 options. Many look up the option codes and assume they mean the same across every model but not always the case.

I get a lot of requests for gear lube info (not just here) and this often comes up with truck owners. Some get misinformed and insist on installing limited slip differential additive in a locking differential. So please excuse me if I get a little abrasive on the subject.

for 2010 GM trucks list of options
G80 Differential, heavy-duty automatic locking rear
GAT All-Terrain Package
GT4 Rear axle, 3.73 ratio
GU4 Rear axle, 3.08 ratio
GU5 Rear axle, 3.23 ratio
GU6 Rear axle, 3.42 ratio

for 2010 Camaro
G80 Differential, limited slip
GM3 Axle, 3.45 ratio
GW6 Axle, 3.27 ratio
JL9 Brakes, 4-wheel antilock, 4-wheel disc

for 2010 Cadillac CTS sedan, sport wagon, CTV-V
G80 Differential, limited slip
J55 Brakes, performance 4-wheel antilock, 4-wheel disc
J56 Brakes, Brembo
J77 Brake, electronic parking
JF5 Pedals, metal
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Re: What kind of diff do I have?

Postby WingNut [OP] » Mar 01 2011, 1:43pm

So back to the earlier post by 99ChevyZ71:
GU6 AXLE,3.42 RATIO
G80 AXLE,REAR,POSITRACTION,LIMITED SLIP POSITRACTION L/SLIP R/AXL(G80)
This is what he posted after I requested the RPOs off my VIN.

So my truck is a 2004 Sierra 1500 2x4 with the Z85 tow package. Assuming 99Chevy's post to be accurate, that locking G80s in 2004 were not standard on my truck, and that in your last post the G80 RPO offers several types of diffs; I do in fact have the limited slip.

You see, what I've been trying to get my arms around (and what seems to confuse many) is the fact that the term "G80" is just an RPO code. Many (myself included) assign the term G80 as a type of Eaton model for locking differentials. Does this make sense?
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Re: What kind of diff do I have?

Postby Z15 » Mar 01 2011, 2:05pm

The G80 does not automatically mean its a Eaton. GM has used Eaton differentials since the 1960's. For instance the differential in my 2002 Trans Am was a G80 but it was made by Torsen. Somewhere I still have the brochure and will look to see if its says G80 and Torsen. I know its says Thorsen in the brochure and I had the factory build sheet that shows G80.

The G80 in my Cadillac is made by Getrag, so no not all G80 are Eaton. In trucks generally speaking yes but who knows what GM might install tomorrow.

I agree, G80 was not standard.

Here is built sheet for the Trans AM, note G80 listed as option, Brochure lists Thorsen as the manf. Also note, car was built on 9-11-2001!
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Re: What kind of diff do I have?

Postby jreagan » Mar 01 2011, 9:23pm

here's a great video of how the G80 locker works
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Re: What kind of diff do I have?

Postby jreagan » Mar 01 2011, 9:28pm

WingNut wrote:So back to the earlier post by 99ChevyZ71:
GU6 AXLE,3.42 RATIO
G80 AXLE,REAR,POSITRACTION,LIMITED SLIP POSITRACTION L/SLIP R/AXL(G80)
This is what he posted after I requested the RPOs off my VIN.

So my truck is a 2004 Sierra 1500 2x4 with the Z85 tow package. Assuming 99Chevy's post to be accurate, that locking G80s in 2004 were not standard on my truck, and that in your last post the G80 RPO offers several types of diffs; I do in fact have the limited slip.


No, for the Sierra, the G80 means the Eaton locker. No friction additive needed.

Folks who get RPO printouts from http://www.compnine.com get the "limited slip" text and think they don't have a locker.

As Z15 clearly showed, for trucks, G80 means locker. For cars, G80 is a 'traditional' limited slip.

I have one in my 04 Silverado (along with the Z85 tow package).

Part of the confusion is that the Eaton G80 locker also has clutch plates inside but used for a totally different reason to lock the axle. [See the video I posted.]
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