Figured I’d make a thread on this and document it as I go. I’ll probably add pictures and a more organized write up at the end as I’m currently in the middle of it.

If you need to replace your transfer case. This may be worth a read. You may be able to save a lot of money and improve the driving characteristics of your h2. In my opinion, GM’s biggest mistake with the h2 is using the Borg-Warner 44-84 transfer case.

1st issue is that these cases were only used in the h2, making them quite hard to come by and pretty expensive. Then, when GM moved from the 4l65 transmission to the 6l80 in 2008, they had to change the input splines on the transfer case to match the 32 spline output on the new transmission. That means that if you’re looking for a transfer case for an 08-09, you will be paying almost 4 thousand dollars… that is if you can find one.

2nd issue is that this is a full-time 4wd transfer case. This setup is extremely clunky during downshifts and when slowing down and getting back on the gas especially when paired with the already clunky 6l80. This is because of the extra gearset in the transfer case and the loose tolerances in the front differential; all this slack adds up, and you feel it as a nasty clunk when driving and can be very annoying and hard on other driveline components. I would be willing to bet that the reason H2s eat transmissions isn’t because of the weight but rather the hell the driveline goes through being full time 4wd.

So what’s the solution then? A part time 4wd swap! And believe it or not. This is fairly simple.

First thing you’ll need is a part time transfer case. The one we’ll need is of the NP263 variety. It is the 3rd strongest transfer case used by gm and should be virtually indestructible in this application. Now you have to be careful on which NP263 t-case you buy. There are 3 variations, the np263(27 spline input), np263hd(32 spline), and the np263xhd(29 spline input). For 2003-2007 H2s with a 4l65, you want the 27 spline input np263. For 2008-2009 with the 6l80, you want the 32 spline np263HD.

The best part is that these transfer cases bolt right up to the original adapter on the back of the transmission. And as far as the 08-09 model years go, the rear driveshaft fits perfect too. The slipyoke sticks out a bit further but there is still more than enough engagement. In fact my driveshaft guy wouldn’t sell me a driveshaft because it would be pointless. As for the front shaft. I don’t know yet, but I think it will work.

As far as 03-07 years, your mileage may vary as far as driveshafts go. I think the np263 might be slightly shorter than the HD variant. But measuring and getting a driveshaft length changed is a pretty easy process. There are plenty of driveshaft shops around and YouTube videos on the subject.

One thing to note is most rebuilders recommend using 5w30 motor oil in these t-cases instead of transmission fluid. It’s slightly thicker and won’t evaporate under high temps… so use that.



So this is the point where I’m at right now. And the truck drives amazing. It’s so buttery smooth to drive. It makes me wonder what GM was thinking when they put the full time case in these trucks. It literally drives like a brand new 2025 truck off the lot now. Traction control still works as expected, there are no codes, and even the speedometer is correct.

Ok now this is where things are gonna get complicated and what I’m working on right now. How do we get the 4wd selector switch and encoder/motor to work? Because right now the truck is 2wd only. I thought about trying to wire up an np263 encoder to the truck, but the encoders work on entirely different principles, so this is impossible. Now, you 03-07 people may be able to pull the tccm, switch, and harness from an 03 Silverado and program it to work, but the redesigned can bus in the 08-09 throws this idea out the window for the newer trucks, but I think I have two ideas that could work.

Idea 1: make a cam that attaches to the oem encoder/motor that pulls on a shifter cable that actuates the case.

Idea 2: take the tccm and encoder from an 03 Silverado and figure out how to make it work standalone from the can bus. First issue is that I think it needs a can signal to verify that the transmission is in neutral before shifting into 4lo. Second issue is the selector switch on 08-09 is rotary based on the headlight switch design. And not momentary buttons like on the older trucks. So I’d need to adapt that too.

If all else fails, I’ll put a shifter on the floor.

Eventually I’ll figure out how to swap in or Frankenstein a 2500 front diff in with the axle disconnect for better fuel economy. I bet it will gain 2mpg from just that. But one thing at a time and it drives great as is.

anyways, that’s where I’m at right now. If anyone has any suggestions or corrections please let me know.

 

I'd go with locking hubs up front to totally disengage the front differential. As for the dilemma with shifting the transfer case, with all the electronics and programming involved, I would go with strictly a manual shift. More reliable anyway. The only dilemma at that point is where to put the shifter. I believe there's room underneath if you put a shifter, lower profile than the transmission shifter, on the left side of that transmission tunnel, going into the side of it. Should be easy enough to fabricate something to hold a bearing on the side of the transmission tunnel, for the shifter to rotate in.
Come to think of it, don't some of the early Ford f-series pickups have the shifter on the left side of the transmission tunnel? Might be able to use some of that hardware.

 

Or you could have just done the 2WD Tcase mod (Transfercases Unlimited) on the BW4494 with a new chain (probably stretched it IS a wear item) and all of your slop would be gone. The electronics will not be an issue and the cost of all the mods you have done negated.

2wd mode with an IFS front differential will not gain you much of anything (MPG or power). You are still pushing the front drivetrain rotating assembly of the differential/CVs with the front tires. Good luck with finding locking front hubs for an H2 IFS that have any strength to them.


https://transfercase.com/
call George 631-226-1448

 

I tore mine apart and the chain wasn't stretched at all. The np transfer case is a much stronger case and with the offroading i do that's a big deal to me.

I figured out I should be easily able to control the np encoder motor with an arduino. It can read the potentiometer input, and the commanded state of the t-case(by reading the led signal on the switch) then turn the motor the correct amount. Will update when im further along.

 

Quick update. Went by Driveshaft Services in Marietta GA(They are awesome I use them all the time). The rear driveshaft is perfect. There is a little more stick out at the slip yoke than factory, but they said that's about where they'd put it if they remade it. As for the front driveshaft, it actually had to be lengthened by about 1.5 inches. Cost me $145.

Still working on getting the case controlled by the dash switches. My pack of N channel mosfets for the arduino came in, and I picked up an encoder motor for a 2004 silverado 2500hd rpo:NP1 and stuck it on there. I had to notch the transmission crossmember quite a bit to get it in, but there's still plenty of meat on it. It was pretty overbuilt and a weird design if you ask me. So far, zero issues.

 

You might try reaching out to Duraburb or Predator Inc. They both do Duramax conversions, and as part of that switch over to the 4wd transfer cases, but retain factory functionality. They may be willing to share some of their secret info with you.

 

Can we nominate this to be “sticky”?

 

Do you have any updates. I did a 4l80 swap. i have a np261 manual and tryed taking the 32 spline input shaft to put in my bw4484 and it didnt fit. i cant find any input shafts from the later model 2008, 2009, hummer tcase

 

I have heard of this being done but ends up being a lot of work. 08-09 t case parts don’t really exist anymore, but if you find an input shaft it should swap over.

You really only have 3 options

1. Swap your 261 in and cut a hole in the floor to mount a lever.

2. swap for an np263hd and buy the standalone wiring harness for it.

3. Get a 27 spline output shaft for the 4l80. These are available online or you can send yours off to a machine shop to be turned. Biggest issue here is it requires tearing down the transmission.