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Ryno

2500HD 8.1 Transfer case/transmission??

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What trans do the 8.1's with the manual transfer case have? I've found about 5 of them I'm considering to buy. Can't put my faith in a button while dealing with snow. What rear diff gear am I looking at as well?

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The manual shift transfer case you are referring to is the New Venture 261 Super Heavy Duty (NV261SHD). The pushbutton case is the NV263SHD. These are the only 2 cases offered behind the 8.1 (and Duramax). That being said you can have either case with the Allison 5 speed automatic (although most dealers ordered them with the pushbutton 263 case). If you want the ZF S650 6 speed manual transmission (which is what I have) the only case that comes behind it is the manual shift 261 -- although the 6 speed is even more rare than the Allison/261 combo! I had to go to Nebraska to buy mine!

 

I'm with you on the manuallly shifted transfer case, I could probably live with an automatic transmission as long as it had the manual case behind it, but besides the (slightly) less reliable nature of the push button case, I feel it takes something away from the 4wd experience :nono:

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On the rear (and front for that matter) axle gearing:

 

*You have a choice of 3.73 or 4.10 with the 8.1/Allison

*4.10 only with 8.1/ZF 6 speed

 

 

I'd look for 4.10, especially if you plan to add larger tires. I doubt you'd see 1 mpg more with the 3.73

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What trans do the 8.1's with the manual transfer case have?  I've found about 5 of them I'm considering to buy.  Can't put my faith in a button while dealing with snow.  What rear diff gear am I looking at as well?

 

 

 

 

I will apologize for the long post beforehand. You can tell I am a strong-headed drive train guy…plus, it may be an entertaining read…..

 

You are a smart man Ryno!

 

I too, went the extra mile to avoid the GM/JD Power philosophy that everybody needs the cream of the crap trucks in terms of options such as the push button unreliable transfercases. When do you really need 4x4? When you really need it right! And that is exactly when the transfer case control module decides to send a blinking message to you instead of shifting the tcase into the “get me out of here gear”. Suks when you are in a life or death area like the freezing cold area of the UP of Michigan, Minnesota or high country of Colorado, Alaska, etc right in the middle of winter when this happens. The bad thing is GM makes you take it based upon seating and audio configurations courtesy of lazy engineering and JD Power influence. Those stooped non-automotive marketing guys are ruining our trucks!

 

This even comes from a GM field rep. I previously spent time on GM tech assist at corp. office helping dealers with diagnostics on drivetrain issues, and Silverado Brand Team before moving on to the field and will tell you this system is worth passing on.

 

When I bought my 01’ HD, GM had a JD Power constraint (dealer ordering lingo) on all manual transfercases due to “customer satisfaction” product requests according to JR Power and Associates…so manuals t-cases were taboo and hard to come by. Even still today.

 

So the only way to get a non-push button t-case at that time was to buy a manual transmission, which requires the GOOD NV261 manual tcase. I was OK with a manual tranny but I really wanted an Allison auto. I am still not fond of ZF’s answer to manual trannies but that is a different story. I would have preferred the NV5600 6-speed as originally intended for the GMT880 series trucks before the NV5600 turned out to be too heavy and took away from the GVWR thus resulting in ZF getting the supplier contract.

 

In the end I think I bought a really rare rig… a 1SB package, K25753 with an 8.1, 6 speed, 4:10’s and manual t-case. Pictures are in my signature.

 

The JD Power/GM relationship is another long story not worth telling here. But….if JD Power disappeared tomorrow, the car guys could live a better life and GM could save a bunch of “shut up and go away” money.

 

Long story short…don’t settle for a dealer stock unit (pattern order) unless they actually have a truck guys truck.

 

No wander Ford and Dodge have ran away with the Heavy light duty truck market.

 

 

On Nov 2, Vote Larry for Silverado/Sierra Brand Team Manager!

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Ok, so what is the answer to the question? Would the tranny code be in the vin, or on the build RPO sticker? I'd like to know, since it will make a difference what truck I buy.

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So along the same line, does the 6.0 offer two transfer cases? I have an 04HD reg/cab auto WT. Vinyl floor mats, 4WD shifter on the floor etc. Extreme winter weather also. Earlier I called the dealer regarding a supposed lag in activating the 4WD on GM vehicles. Said that was fixed now and it only takes about a couple of seconds for the solenoid? to pull it in. But he didn't ask how I put it in 4x4. Did he assume a push button? Is the floor shifter a different transfer case? I guess I could call the dealer but you guys are more interesting. Except let's not talk about dmax vs. 8.1 haha.

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Ryno,

 

Guess you were not very clear on the question. You never asked for RPO codes only which tcase does it have.

 

There will not be a transmission RPO code that will dictate the transfercase. You can look for RPO NP2 Manual Transfercase. Because the manual shift transfercase is actually standard (yes, standard on Silverado’s) the RPO code may not appear anywhere except the Service Parts Identification Label in the glove box. For that matter, look in the window and see if you see a stick on the floor.

 

NP2 Manual shift for HD and LD

NP1 is electric shift for HD trucks

NP8 is electric shift (autocrap) for non-HD trucks

 

Major,

 

Yes, the HD’s have two different transfercases. The manual NP261 and electric NP263

 

You dealer probably did assume buttons because shifting delays have been an issue for them but the delay could also be related to the front axle disconnect which is the same for manual or electric transfecases. Have not really heard of a delay with the front axle disconnect since the old thermal actuation disconnects were canned in the mid-90’s.

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Thanks Larry. Look's like the manual TC still has something else involved to actually ensure you're in 4wd aside from me pullin er in. I had a NP 205 on a suburban. You pulled that in and that was it. Things change. Heck, I remember back when I worked at a Chevy dealer in '72, the "NEW" '73 style trucks were coming out. They were selling CST Blazers at whatever cost because they were the "'OLD" style. I think the new thing was a NP 208. Fulltime or something. You can tell I didn't stay in the automotive field. Oil embargo of '73 '74 kept me at $1.65 an hr. :cheers: Moved on.

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Major,

 

You’re right on the old 205’s. Pull the lever and your in. Manual transfercases of today work the same way. The big difference between the new and old (205, 203, 208, etc) manual transfercases is actually how the front axle is engaged. The old ones used manual locking hubs while the new ones use an axle disconnect. Some years the disconnect was vacuum operated, other years they were thermal electric and now they are fully electric. None of them are all that reliable compared to the old manual locking hubs. But of course, none of today’s truck owners would stand for getting out in the cold or mud to turn the dials…heaven forbid....except for me.

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Ryno,

 

I think what your asking is what "transmission" does it have .

 

These guys sometimes try to "overexplain" them selfs lol :cheers:

 

If it's an 8.1 and it's an Automatic, it's an Allison regardless of the transfer case.

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Steve-

 

THANKS!! I was hoping that would be the answer. Would hate to have a 4l80e behind a big block. You just made my weekend!

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Ryno,

 

I think what your asking is what "transmission" does it have .

 

These guys sometimes try to "overexplain" them selfs  lol  :(

 

If it's an 8.1 and it's an Automatic, it's an Allison regardless of the transfer case.

 

 

 

You are probably right. But I thought they used to mate the 8.1 with a slightly beefed up 4L80E aka 4L85E as the default, while offering the Allison as an upgrade at one point. Maybe not

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Ryno,

 

I think what your asking is what "transmission" does it have .

 

These guys sometimes try to "overexplain" them selfs  lol  :(

 

If it's an 8.1 and it's an Automatic, it's an Allison regardless of the transfer case.

 

 

 

 

As much as I love my Allison, there is no engine in the GM arsenal that a 4L80E (or Turbo 400) couldn't handle. I've positively abused a slightly modified Turbo 400 behind a Ram Jet 502 and it didn't even blink. All this in a 7200lb 1990 GMC 4x4 1 ton dually. I sitll have the motor, wish I still had that T400.

 

Still, I absolutely adore my Allison. But don't think the 4L80E is weak..it ain't!

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What trans do the 8.1's with the manual transfer case have? I've found about 5 of them I'm considering to buy. Can't put my faith in a button while dealing with snow. What rear diff gear am I looking at as well?

 

I noticed that you have an '02. Here is something to think about...

 

I do not know if the issue of the year is true for the non-electric/manual transfer cases.

 

I have been researching this topic recently and have found that if it is behind a Allison, and it is a first or second year (01,02), you can not interchange the NP263 and the NP263XHD. Obviously, I have the electrical 4x4 switch.

 

Can somebody shed some truth to this statement?

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No matter what....................The front wheels are still

engaged by a ELECTRIC signal no matter if you have a

lever on the floor or a button on the dash..............

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