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Drivetrain - 2001 - 2010 Discuss front and rear axle, transfer case, brakes, etc. Transmission questions belong in the appropriate transmission forum below. First through fourth generation...

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Old 07-22-2019, 01:06 PM   #1 (permalink)
Ermanno
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What Differential Do I Have

2002 2500HD
Is there somewhere on truck or vin# that tells you which diff is in your truck.

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Last edited by OkDually; 07-22-2019 at 01:09 PM. Reason: prefix
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Old 07-22-2019, 02:17 PM   #2 (permalink)
davester
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in your glove box, there should be a sticker with a whole bunch of 3 letter/digit codes, known as RPO codes. They list the options/features in your truck.


It'll have GT4 or GT5 (most likely GT4) indicating you have a 3.73 ratio.


If you want to know info about the rear axle itself (like if it's a 10.5" or 11" or whatever), the RPO codes don't have that level of detail, someone else should be able to tell you what it most likely is, or you can look at the bolt pattern of the diff cover and measure it to figure out what size it is.

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Old 07-22-2019, 02:32 PM   #3 (permalink)
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...or maybe G80 for the "gov-lock" differential. Put that in the search and you can read arguments about this one for days!!
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Old 07-23-2019, 10:16 AM   #4 (permalink)
Rvn4me
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11.5" 3.73:1 American Axle
RPO in glove box for type of differential should be G80
You have an Allison automatic or ZF6 Manual?
https://www.dieselplace.com/forum/76...-have-g80.html

Last edited by Rvn4me; 07-23-2019 at 10:26 AM.
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Old 07-23-2019, 11:23 AM   #5 (permalink)
Ermanno
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Quote:
Originally Posted by Rvn4me View Post
11.5" 3.73:1 American Axle
RPO in glove box for type of differential should be G80
You have an Allison automatic or ZF6 Manual?
https://www.dieselplace.com/forum/76...-have-g80.html
http://www.youtube.com/watch?v=ftyJvIO0DZ8
Ok I had a look in the glove box, there’s a GT4 and G80.
So is the 3:73 better for pulling heavy loads or a highway gear.
I have an Allison Automatic
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Old 07-23-2019, 12:00 PM   #6 (permalink)
jake111
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The Duramax should have enough power with that rear end to pull your load up a telephone pole (if you could get traction, but might only be a small exaggeration )

[added on edit] And that's already a tall gear for highway use, unless you want to go really fast all the time. Unless there's something wrong with the diff, it's best to leave it as it is.
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Last edited by jake111; 07-23-2019 at 12:03 PM.
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