NP246/266 custom build

[chrisuns]

I figured I share a little project I've been working on for about a month or so. It is a 05 np246 I bought on craigslist cheap $200.00. Something I've always wanted was an AWD duramax, so I figured I'd build this up to handle the power that my truck pushes out - rougly 950 Ft Lbs.

I started out with updating the clutches to Raybestos GPZ's, then I milled down the apply plate to accept a few more clutches - if my math is correct I should have roughly 1500-1700 FT Lbs of clutch holding power, while this sounds like a lot, recall the allison has a 3.01 first gear+ torque converter multiplication. However, it's very unlikely the front will ever require that amount of power in my application (My truck hooks very well for the most part, it's the rain and under 50F I have trouble).

Then I addressed the bearings with new Koyo's and upgraded the apply bearing to a higher capacity unit; it also uses the 1" double row input bearing from a 263xhd - requires machining the front case. The output bearing is ironically stronger in the 246 than the 263XHD - the 246 deals with axial loads from the clutches applying though.

From there, I went to the 263XHD chain and sprocket set. These are 1.5" roller pin vs. the np246 1.25" rocker joint. They make a 1.5" rocker joint chain; but, R.J.'s are weaker than R.P.'s, the exchange is R.J.'s are more efficient and create less heat.

Some misc where a 360 degree output bearing split ring retainer(you can see in one of the photos); aluminum rear case half, the associated wiring; switch, and controller - Likely a few things I've forgotten

Anyways, any questions feel free to ask!

 

[chrisuns]

Also, I did loose a bit of strength in terms of the output shaft, as that's where the NP263XHD is 1.5" vs the NP246 1.25. Not too concerned for my application, as I have ran the numbers and have a great cushion before that fails. I wouldn't recommend it for 750+hp duramax's though :happy2:

I also added the 6 pinion planet too - knew I forgot something! Probably forgot more, all in all it should be a stout unit - especially with the cooling and filtering system I'm making for it.

 

[c20elephant]

Wish I had the time and wherewithal to turn my 2x4 truck into an all wheel drive truck, what year trucks do the transfer cases come out of.?

Let's see..

Transfer case.

Output shaft on the transmission.?

New yoke for rear driveshaft.

Cut down existing drive shaft or buy a new one.

CV axles.

Front differential assembly.

Front drive shaft.

New front cross member.

Is here a mount and hole to be drilled in the frame for the IFS.?

Might have to buy new hubs as I don't believe mine are machined for the CV sahfts like my 2007 2x4 2500HD NBS gasser was.

No 4x4 wiring to mess with.

Sounds like a fun truck to drive with all wheel drive......:thumb:

 

[Chevy1925]

OP, what are you going to do for cooling or will you be doing anything for cooling? always been curious of the temp these t-cases reach, throw in a heavier truck and more power, i dont know if that fluid will like you long lol

 

[slipclutchms]

Awesome. Love reading about stuff outside the box.

 

[Harbin_22]

Funny this came up, Me and JoshH were just talking about this the other day. Curious to see how this works out

 

[Ridin'GMC]

Interesting subject. Definitely interested in this for a street truck project. Hope it all works out well for ya.

 

[IOWA LLY]

Very cool project! Curious how it will work once done.

Sent from my SM-N920V using Tapatalk

 

[chrisuns]

Wish I had the time and wherewithal to turn my 2x4 truck into an all wheel drive truck, what year trucks do the transfer cases come out of.?

2005-07 246 is what you're after for something like this; preferably post-06 as the clutch assembly is press on the shaft to reduce noise and chatter, prior models (03-05) use a software calibration where the clutch is partially applied it 2wd to get rid of the noise.

Frame wise, I couldn't say; I've never been under a 2wd to tell what parts are different.

Tomorrow I will upload a few more photos, I didn't think anyone was really interested in this so I didn't go into too much depth, haha!

 

[chrisuns]

OP, what are you going to do for cooling or will you be doing anything for cooling? always been curious of the temp these t-cases reach, throw in a heavier truck and more power, i dont know if that fluid will like you long lol

For now, I'm going to run it straight without a cooler and monitor temps via the drain plug. I'm buying an arduino and going to program it to run my fuel pump via throttle % and the transfer case pump via temp and vehicle speed(so I don't run the pump at 100% risking running the cases pump dry) and timer (for filtering if the temp requirements aren't met).

The filter head is just a 1-14 hydraulic filter and a napa filter head. Cooler will be a derale fan unit.

I'm still making the cooling circuit. I'm not too concerned for now as I'm not going to abuse it... yet. Also, I'm using synthetic dex3 (mobile 1), the later models don't really require as much friction modifiers as the pre-loaded clutch units (02 and prior) and if I find the clutches chattering excessively, I have a synthetic friction modifier I can add.

 

[chrisuns]

Very cool project! Curious how it will work once done.

Sent from my SM-N920V using Tapatalk

I should find out today or tomorrow, just waiting on the UPS man to bring me my new centerlink

I didn't want to go fuel throttle and break traction and have this thing engage the clutches and kill my steering lol. So I got a cognito system - similar to dmax stores and rare part pitman arm.

The other time has just been spent remaking harnesses and adding intellibeam and automatic windshield wipers from an STS.

 

[JoshH]

Funny this came up, Me and JoshH were just talking about this the other day. Curious to see how this works out

This is just a little different than what you and I were talking about. He's using an AutoTrac transfer case that has a clutch inside that engages the front driveshaft when it senses slippage. I'm not really sure how they work since I've never messed with them, but that's the way I understand it. It is a cool project though.

 

[chrisuns]

Got everything going, I like it; it does appear it needs a slight bit of friction modifier, as it's a bit grabby during low torque traction loss (gravel).

Now, launching it from 2-2.3k rpm, it took of like a gtr, lol! Ass end slides out ever so slightly and then just rips! I does NEED a cooler using it like that though - I haven't hooked up the gauge, yet. However, it was much hotter than a 263 would ever get by touch alone.

It'll be interesting to see how those GPZ handle it? I plan a tear-down in 2k miles.

 

[02CCSB]

Not sure I see the point of this swap. Once the clutch is fully applied, it would act the same as a 263 in 4HI. With the clutch partially applied with 950ft lbs it would likely slip the clutches and cook them. This seems like a lot of work for no real world gain. Would probably have been easier to use an NP149 with a viscous coupler from a Siverado SS but that has no low range and would probably cook the coupler in short order. Basically, I'm having a hard time understanding the up side of this swap?

 

[TheBac]

Chris, thats a pretty damn cool idea. So under stock conditions, you think this will hold up just fine? Did you have to make changes to the electronics to make this work? And what about the switch in the dash - did you have to change it to the Blazer-style AutoTrac one?

This kind of thinking was the bedrock this forum was originally started on and thrived on. Nice to see someone still thinking instead of simply parroting something they heard.

 

[Awenta]

What senses the slippage in these units and controls clutch apply? I wonder if you could make a module to manually control apply pressure? I haven't messed with one ever so this might be completely impossible.

Sent from my SM-N910V using Tapatalk

 

[02CCSB]

The transfer case control module compares rear output and front output speeds and applies the clutches accordingly via the encoder motor. My question is, if GM didn't think this would work and last in a stock application, hence it never coming on anything heavier than a 6.0 1500HD, what's the point in making it work behind a 1000ft lbs diesel? Like, ok, different idea, innovation blah blah blah, but to me, this makes about as much sense as putting a 4L60E in it...

 

[chrisuns]

Chris, thats a pretty damn cool idea. So under stock conditions, you think this will hold up just fine? Did you have to make changes to the electronics to make this work? And what about the switch in the dash - did you have to change it to the Blazer-style AutoTrac one?

This kind of thinking was the bedrock this forum was originally started on and thrived on. Nice to see someone still thinking instead of simply parroting something they heard.

Yup, all new wiring harnesses that I made from parts I purchased off mouser. Then the TCCM programming and the switch from a silverado/tahoe.

Hard to say in real world, for now. I have pages of papers where I did numbers on various parts and gave them gracious stress factors - In time we'll see what it can handle. The cases for the most part are pretty stout units that are plagued by the electronics and things like case wear, rear snap ring groove from the clutches applying, chain issues and poor maintenance - things which I've addressed (minus the electronics; I mean I've updated the wiring to higher gauge and solder+crimps; but the encoder sensor is a high failure item).

This is untested and I wouldn't go recommending it yet. I know this will be a high maintenance modification and require watching it, but that's half the fun for me - I enjoy tinkering

Not sure I see the point of this swap. Once the clutch is fully applied, it would act the same as a 263 in 4HI. With the clutch partially applied with 950ft lbs it would likely slip the clutches and cook them. This seems like a lot of work for no real world gain. Would probably have been easier to use an NP149 with a viscous coupler from a Siverado SS but that has no low range and would probably cook the coupler in short order. Basically, I'm having a hard time understanding the up side of this swap?

Just something fun to do. The 149, 4484 and MP2225 where options I looked at too, and may try when I'm bored with this. However, they require having a custom input shaft made or custom output made of the allison or custom speed sensor setup (mp2225: Plus, this case runs about 2 grand from the cheapest source I could find).

The transfer case control module compares rear output and front output speeds and applies the clutches accordingly via the encoder motor. My question is, if GM didn't think this would work and last in a stock application, hence it never coming on anything heavier than a 6.0 1500HD, what's the point in making it work behind a 1000ft lbs diesel? Like, ok, different idea, innovation blah blah blah, but to me, this makes about as much sense as putting a 4L60E in it...

I like it, drives like an awd vehicle in DD, then when I apply heavy throttle it just takes off without fuss and ramps down the clutch rate and I can turn without hopping etc.. No different than adding 100-200% HP to a duramax - GM didn't intend for that to be possible either.

 

[chrisuns]

I tried to upload more photos, but it is saying I'm missing a security token??

So far everything is working flawlessly, minus one issue! I ended up frying an encoder motor; however, I have my suspicions it was bad from the get go - it acted as if it was always slow to bias torque to the front, which felt cool(similar to a gtr); but indicated clutch slip (heat).

Story: It rained here a few days ago and I went on a winding road and frankly, I drove it in an abusive manner; suddenly, the 4x4 indicator lights went blank, followed by service 4x4 - the TREC (4X4 control) fuse popped.
I replaced it, but nothing. I took the encoder apart and it smelt like burnt copper (motor was fried).
The TCCM should have shut down the encoder motor prior to this happening, which gives me reason to suspect the coils where bad from the get go, that and the general slow reaction to adjust to slip.

So I replaced the motor with a new one and waaay different driving experience. The system acts as if it will anticipate slip vs reacting when you floor it. Prior, you would launch it then the rear would slip and the front would kick in.
Now, you when launch it and it's as if you're in 4-high and then it disengages when you let out of the throttle. It is also smoother, similar to the feel of the newer magna 3023/3024 active cases that comes with the newer 2007+ trucks/suvs

I've put it through some abusive tests since the new motor as well - Including launching from 3k rpm and blowing all 4 tires off (well 3 tires technically) and it didn't miss a beat. Time will tell if this has been detrimental to the clutches. I've approached 500 miles on the case and will disassemble at 2k.

I also intend of buying a "china" Tech II to see what % the encoder is traveling to correct for slip. The clutches feel awesome, at first they where grabby, so I corrected this by adding a 1/2 dosage ( 1 once) of friction modifier (Lubegard 61910) to the mobile 1 synthetic ATF - this corrected any clutch chatter during engagement.

The sum thus far is: My FAVORITE mod to my truck outside of EFI Live!!! :happy2:

 

[JoshH]

I guess I need to do a little more research into how this transfer case actually works. It sounds like it uses the encoder motor to apply the clutch to engage the front axle based on slippage, and the application is variable in the amount of pressure it applies. That is a little surprising to me. I would have thought it would either fully engage or fully disengage to prevent damaging the clutch. I notice you aren't using the AutoTrac fluid. Is the synthetic ATF supposed to be better?