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6 speed Allison mated to a lb7

6K views 6 replies 3 participants last post by  BoiseRob 
#1 ·
A 2004 lb7 GMC 2500 crew cab short box has just come into my possession, before I got it the front differential didn't disengage and blew the u-joint in between the front driveshaft and the t-case. That sent the driveshaft flying around and it smashed the trans at 120 kph breaking the shift linkage off and putting a hole in the transmission case behind where the shift linkage is. I want to know if it is possible to put a 6 speed Allison from a newer Duramax and what any problems I would have because I've been searching for a while and haven't found anything on putting a 6 speed into an lb7 truck or any other truck that had a 5 speed for that matter. anything would be helpful, thanks
 
#2 ·
From what I have read, your 2004 Alison is already a 6 speed. you just have to buy the conversion valve body along with getting the Transmission control module remapped. i'd say it's a 2500 to 3000 upgrade but the trans itself already has the gears!
 
#4 ·
From what i have read, they are the same transmission. However, you would most certainly have to get the TCM reflashed. Just search 5 to 6 speed conversion and you'll find all the info you need. it will be my next upgrade after i sort out the fuel in my oil!
 
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