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GM NV263/261 vs. NP205

Nick 6.5

Nick 6.5

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Location
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so im torn on what to do. Im getting ready to do a duramax swap in my 1996 2500HD detroit 6.5. i love the allison but am weary of the chain driven slip yoke 261 and 263 t-cases. i would love to marry the np205 to the duramax allison combo and i know people have done it but what about the torque? i know the np205 is rated to 1500ft/lbs. im not going to keep the duramax stock and frankly dont know how much power i will end up producing in the future. obviously things will break with large amounts of power. i know the 261 and 263 can handle the power easily to 1500ft/lbs but i really dont like the idea of slip yokes cuz i will be using it for off roading as well as towing and have bad experiences with slip yokes. i guess this post is more or less to get the standpoint of you guys and to help me decide what to do while everything is out before installation. Thanks in advance for any replies!
 
Do the pump rub fix to the NV and you should be good. For reference I am at 230k+ and have never had the rub through. ...yet.

Sent from my SCH-I535
 
my donor truck has 214k i was told. i havnt recived the truck yet its on the transporter so idk yet exactly what case it is. what t case does your truck have do u kno?
 
btfarm said:
Do the pump rub fix to the NV and you should be good. For reference I am at 230k+ and have never had the rub through. ...yet.

Sent from my SCH-I535
Click to expand...

Mike you might consider a fix before you get a leak, the Tcase half is over $300..

Pump rub fix:
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10001.jpg
 
I'm at 220k hard towing miles and no pump rub. My gpas 07 classic w/ 6.0 did it at 170k and our 01 8.1l dually has it at 280k.

I think there is a slip yoke eliminator from 4x4 shops for lifted off road style trucks.

Source Unknown
 
The NV261/263XHD is quite a bit STRONGER than a 205. To many people get hung up thinking the NP208's massive weight equals strength, but in reality it does not. Also don't forget that if you go to a NP205 you will need a billet extension housing for the ALLISON, and either have to have one of the super rare late model 205's with an output speed sensor in it or make your own tone wheel and install a speed sensor in the extension housing.
 
ive had alot of np205 tcases and never had a major problem with them. they are strong there is no doubt about that at all. and yes i know about the spacer that will be needed as well as the spline swap for the allison 205 marriage. the speed sensor can be bought new from a store and modified to work on the 205 with the gear. i know the 261/263 are strong i just dont like the slip yokes. and the slip yoke eliminators are expensive for these t cases. for the price of elimintaing the slip yoke i can buy a used 205 and rebuild it and install it for cheaper than the slip yokes. ive seen just the rear slip yoke eliminator go for 600$ in addition id need the front as well. thats just my idea and trying to see other peoples ideas or thoughts.
 
Nick 6.5 said:
ive had alot of np205 tcases and never had a major problem with them. they are strong there is no doubt about that at all. and yes i know about the spacer that will be needed as well as the spline swap for the allison 205 marriage. the speed sensor can be bought new from a store and modified to work on the 205 with the gear. i know the 261/263 are strong i just dont like the slip yokes. and the slip yoke eliminators are expensive for these t cases. for the price of elimintaing the slip yoke i can buy a used 205 and rebuild it and install it for cheaper than the slip yokes. ive seen just the rear slip yoke eliminator go for 600$ in addition id need the front as well. thats just my idea and trying to see other peoples ideas or thoughts.
Click to expand...
To RELIABLY run a NP205 behind an ALLISON in a high HP lifted application you will need a lot more than just a spacer and an adapter for the splines. The ALLISON's extension housing is KNOWN for cracking when a driveshaft gets out of balance or a bad u-joint. This I with a magnesium cased transfer case that weighs roughly 75 pounds installed full of fluid. Now in steps the NP205 coming in at roughly double the weight and you have a recipe for disaster. And if you install the spacer to run the adapter for the splines you will put even more leverage on the already over stressed extension housing. just my opinion, but I think you would be setting your self up for trouble unless you bought a SUNCOAST billet extension housing for the ALLISON. Then you have the different transfer case ratio which the TCM may or not like(you can change the ratio in the TCM with EFILIVE, but many have reported that this doesn't actually fix the issue and the TCM gets pissed off in reverse in 4 low and goes to limp mode and leaves you with neutral ONLY). So now your back to having to install the speed sensor between the trans and transfer case to make it shift in 4 low reliably.
 
ok i didnt know about the weak extension housing the second housing speed sensor i did tho. have u had any problems with the slip yoke application?? my goal isnt for a rock crwaler dont get me wrong. i just hate when the yoke slips out of the tcase while off roading it makes it a pain in the ass cause usually u have to try to get to level ground to reinstall.. again not a rock crawler just a trail rig that can get to my modded 79 scottsdale when i break it on the trail... seems like it may be more trouble than it may be worth...
 
I haven't had any trouble, and a lot of guys run one piece driveshafts without issue. The stock yoke is pretty long as it is intended to have a lot of contact area.
 
Thanks for the info guys! i finally get my donor truck today so ill be able to see what tcase i have. hey ferm would it be ok if i messaged u about problems i may run into with wiring and such?
 
Do u by anychance know the difference between the nv261 and 271? i know they come in dodge and ford and have higher ft/lb rating but is that all? they look the same physically and even look like they will bolt up to the allison and also have no slip yokes. i got my donor truck and turns out i have the push button 263. im only asking on here cause i cant find anywhere that will tell me specifics
:mad2:
 
The 271 is a beast of a transfer case. It was offered in FORD and DODGE applications only that I know of. The problem with that is the clocking is 90 degrees off from GM's clocking, so you would need a clocking ring to make it work. A think a few sled pullers have tried to convert to them, but most just get a slip yoke eliminator for the front shaft and call it a day.
 
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