Gear Ratio

TJV20018.1 · December 28, 2004

I just purchased a 2001 GMC 2500HD with the 8.1/Allison. I was wondering if there was a way to determine the gear ratio by the VIN number. My RPM's are right at 2000 @ 70 mph.

Thanks

496 CUBIC INCHES · December 28, 2004

No, the VIN doesn't contain the gear ratio. If you're running 2000RPMs at 70 you have the 3.73s. My truck with the 4.10s runs 2000RPMs at 60mph.

On edit,

The option codes are on a sticker in your glove box.

GT4 is the 3.73s

GT5 or GT8 are the 4.10s

Bart2500HD · December 28, 2004

You can call your local dealer and give them your VIN and they can look it up for you. Before I bought my HD, I had a buddy at my Chevy dealer print me out a list of all the options on my truck. It comes in handy sometimes.

GM-Tech · December 28, 2004

I just purchased a 2001 GMC 2500HD with the 8.1/Allison. I was wondering if there was a way to determine the gear ratio by the VIN number. My RPM's are right at 2000 @ 70 mph.

YOU can't tell by the VIN, but I can. If you give me your VIN, I can run it through GMVIS and get all your option codes... which you could also get off your option label in the glove box. Axle RPO codes typically start with the letter "G".

If you want to PM me your VIN, I can tell you what you want to know. Alternately, get all the option codes that start with "G" and I can tell you from that.

TJV20018.1 · December 28, 2004

Thanks, I will get the codes.

dewfpo · December 28, 2004

You've got 3.73's based on 2k rpm at 70 mph.

DEWFPO

MS3DALE · December 29, 2004

Yes,I believe 3.73 was the only gear ratio available with the 8.1/Allison in '01.

But like GM-Tech said the VIN will tell us because we can run it on GM-DealerWorld. Any "nice" dealer will do this for you,I do it all the time.

As he also said you can get your "G" codes out of the glovebox and one of us will let you know or you can go to the RPO code link on the homepage here.

BBSilverado · December 29, 2004

yep you have 3.73's that is all that was offered with the allison

My 8.1/Allison is 2000rpm at 70

and my company truck is about 2000 at 62 (6.0L w 4L80-E)

BBSilverado · December 29, 2004

GT4 = 3.73

GT5 = 4.10

G80 = locking differential

Bgdsub72 · December 29, 2004

GT4 = 3.73
GT5 = 4.10

G80 = locking differential

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these codes can be found on your SPID label (service parts Identified) which is located in you glove box.

496 CUBIC INCHES · December 29, 2004

Yes,I believe 3.73 was the only gear ratio available with the 8.1/Allison in '01.

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Nope,my truck is an 01 and has the Allison and 4.10s.

MS3DALE · December 29, 2004

You know maybe I was thinking of the Duramax/Allison combo only being available with 3.73's. I'll have to check my order guides from '01-'02.

Does anyone have a Duramax/Allison with 4.10's?

1BADHD · December 29, 2004

You know maybe I was thinking of the Duramax/Allison combo only being available with 3.73's. I'll have to check my order guides from '01-'02.
Does anyone have a Duramax/Allison with 4.10's?

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Dmax only came with 3.73's. Not matter what tranny you opted for.

8.1's can have 4.10's. But they are pretty rare to find.