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Discussion Starter · #1 ·
Is there a difference between the allison behind an 01 seirra 2500hd with an 8.1 vs a 02 sierra 2500hd with the duramax. (long story short im trying to find a core and i may have found one.)
 

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i thought the tranny behind the 8.1 was a 4l80
 

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I would think maybe the TC but beyond that I would think they are the same. Inersted to know.
 

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I would think it'd be at most the converter and TCM programming to work with the 8.1 powerband. Other than that I dont know what they would change or why.
 

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On the 3/4 ton suburbans and avalanches they used a trans other than the Allison. The 2500HD+ pickups had the allison. Family used to have one, could really hear the trans over the engine at low speeds.
 

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Discussion Starter · #8 ·
cool. im just after the case and such to rebuild so i should be in good shape then? theres not a different spline shaft or front pump or anything internal in the valve body to acomidate the different power band??
 

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I have a 8.1 and a Duramax and the transmission does feel different but that could be more due to the engine than the trans. If you have a decent dealer close to you you could have the parts guy run part numbers and do a comparison.
 

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I have a 8.1 and a Duramax and the transmission does feel different but that could be more due to the engine than the trans. If you have a decent dealer close to you you could have the parts guy run part numbers and do a comparison.
Why would you do that when they are the same?
 

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Just a suggestion in case the tc or any thing else is different. If they are identical then great. Half into a project and realize there are settle differences really sucks.
 

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Just a suggestion in case the tc or any thing else is different. If they are identical then great. Half into a project and realize there are settle differences really sucks.
The converter is different and the TCM strategy is different. The Allison is the same. If you don't believe this than go see your GM parts man.
 

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No reason to doubt it. Thanks for the good info. Can the tcm from a 8.1 be used for a duramax and just get reprogrammed? Just trying to learn more info on these trucks thanks again
 

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No reason to doubt it. Thanks for the good info. Can the tcm from a 8.1 be used for a duramax and just get reprogrammed? Just trying to learn more info on these trucks thanks again
yes, the TCM's are the same. It just has a different operating system/calibration loaded into it.

You can reflash an 8.1 TCM with a duramax calibration and it will work fine.
 

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Ok i'm looking at a 03 allison off of a 8.1. Everyone is always talking about reflashing the tcm but why cant i just take the trans put it in and hook to my old dmax ecm. Is there anything other than sensors and actuators in the trans? and are they any different than the ones in a dmax?
 

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Ok i'm looking at a 03 allison off of a 8.1. Everyone is always talking about reflashing the tcm but why cant i just take the trans put it in and hook to my old dmax ecm. Is there anything other than sensors and actuators in the trans? and are they any different than the ones in a dmax?
What year is your Dmax?
 

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This is why I love this site. Other people thinking up ideas and others chiming in with information. :thumbsup

So I could find a wrecked 8.1 2500, steal the trans, rebuild it, and use it if I got everything calibrated?
 

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Depends on the year. Think the earlier trans had a different bell housing & cooler line connections
 

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i thought the tranny behind the 8.1 was a 4l80
I have a 2002 2500HD with the 8.1L Gas and the 5-speed Allison.
I don't know if the Allison was a mandatory option though.
 
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