np136 vs np236

[photo_van]

You will probably find that different length adapters correspond to different length input gears, at least that's what I found to be the case when I did the 242.



I wouldn't count on the clocking being correct either, as we have seen them vary in GM applications. So you may need one of these.



As for low range sync, check out this around middle of page two viewtopic.php?f=58&t=7844&start=15

[racrx7]

But we knew that, right? Apparently they used this in “light duty” applications, the 231c I have is of the same pattern. No big problem, because we know that GM also makes a 6 bolt patterned trans/TC adapter because they are for sale ($50) on ebay. I think this is used in the ‘99 and up Astro with the NV136? It looks like this

I believe the TC adapter on the '99 and up NV136 is still the 5 bolt on the TC side. Unless I missed one hiding while counting. I'll double check. (I've been trying to get rid of the last remnants of contaminated Dexcool for the last two days. I think its all out now, thanks Oxcalic acid ). The 6 bolt adapters I've seen at my local PNP are for the NV246 that are behind the 1500 series Tahoes/Suburbans.

[photo_van]

But we knew that, right? Apparently they used this in “light duty” applications, the 231c I have is of the same pattern. No big problem, because we know that GM also makes a 6 bolt patterned trans/TC adapter because they are for sale ($50) on ebay. I think this is used in the ‘99 and up Astro with the NV136? It looks like this

I believe the TC adapter on the '99 and up NV136 is still the 5 bolt on the TC side. Unless I missed one hiding while counting. I'll double check. (I've been trying to get rid of the last remnants of contaminated Dexcool for the last two days. I think its all out now, thanks Oxcalic acid ). The 6 bolt adapters I've seen at my local PNP are for the NV246 that are behind the 1500 series Tahoes/Suburbans.

I do believe you are correct. I was guessing at that back then hoping someone with a newer van might chime in! It may be that all the small GM TC's (231, 136) were 5 bolt and the NV24x GM were 6 bolt (just to make things confusing): Jeep and Dodge use the 6 bolt (different pattern than GM!) for all their NV TCs, or at least the ones I've had my hands on. I was recently scavenging from a 241c; it was 6. Good luck with your quest!

[racrx7]

For anyone still following this and still interested, here is some info I gathered researching an NP246 swap into an AWD Astro van. I will also be doing a complete build of a hybrid 236/246 TC with photos and notes to post later on a build thread. Work Schedule permitting of course.

So, I have 2 TC's open and in parts. A 236 and a 246. Function and components of the two are very similar with a few acception's. The 236 uses a 3 pinion planetary reduction while the 246 uses a heavier duty 6 pinion. They are interchangeable between the two models. The 236 uses 8 frictions and 7 steel plates in its clutch pack and has a shallower drum than the 246. The 246 uses 10 frictions and 9 steels in its clutch pack build up, and has a deeper drum to hold them in. The frictions and steels of the two T/C's are the same physical size and construction. The main shafts of the two are the same and interchangeable. The input shafts are the same 27 spline inputs and are interchangeable. They also use the same input bearing and seal. The front differential output shafts however are NOT the same nor interchangeable. The 136/236 uses a male splined version with a smaller bearing and seal while the 246 uses a female spline version with a larger bearing and special 2 piece seal. The 246 front diff output shaft also uses a larger cage bearing at the rear. That being said, while a 246 rear case half will physically mate up to the 236 front half, it cant be used because of the larger rear cage bearing. The 236 uses a 1.00 inch chain while the 246 uses a thicker 1.250 chain. The 246 chain AND sprockets will fit the 236 shafts perfectly with no case clearance issues. I mocked up my 236 case with all the usable 246 internals and they all fit perfect without any clearance issues. The cases of the two are different and not interchangeable. The 236 uses a 5 bolt pattern to the trans adapter while the 246 uses a 6 bolt. As Captain Crunch has already proven, the 236 TC will bolt right up to our existing transmission adapter and uses all the same drive shafts. The 236 case even has the mount pad on the front case half to accept the brace that is used on the factory 136 TC. So why all this when a 236 should work just fine behind our applications? Because I wanted to see if a really heavy duty TC could be assembled using parts available. Why not just fit a 246 behind the trans? That requires a different trans adapter, cross member modification, and drive shaft modifications.
The heart of these two "Autotrac" cases is the clutch pack assembly and how it is set up. "99 to around 2003 use what is called a preloaded clutch pack set up. Somewhere after "03, they went to a NON preloaded clutch pack assembly. Why did they make the change? MY understanding is that in colder climates, the front differential lube tended to be super thick and viscous in very cold temps and even when the front axle was in disconnect mode, it caused resistance and slipping of the clutch pack, possibly shortening their life. One recommendation was to replace the front diff lube with synthetic. So sometime after "03 came along the NON preload clutch pack setup. It requires several different internal components to make it all work. Not a cheap conversion, but doable. The clutch pack hub, pressure plate and return spring are totally different, but can be used in the existing clutch drum. The shift lever is different and has a totally different cam profile and doesn't use the detent spring. It also requires a different clutch apply lever in conjunction with the different cam profile. The new style shift lever is also of a splined shaft that fits into a splined encoder motor. So the old style encoder motor with the two flats for shaft engagement cant be used. If a post "03 TC ever shows up at my local PNP yard, I'll pick it up and dissect that one too. For now, I'll use what I have. I also have all the wiring, plugs, switches, TCCM's blah blah blah to hook all this mess up. Should be interesting.

As I mentioned before, I'll do a full write up build with pics soon. I have all the new bearings, clutches, seals chain and the special clutch pack set up tool for the build. Stay tuned

[photo_van]

sounds like a fun project. It's a great thing about NV/NP transfer cases, many parts are interchangeable throughout similar series. The 6 pinion planetary is a good way to go; I pulled one out of a 241.

[racrx7]

The 6 pinion planetary is a good way to go; I pulled one out of a 241.

Yes sir, Drops right in

[Captn. Crunch]

Nice work with the parts swapping. I'm for sure interested in the six vs. three planetaries and wider chain. A word of caution here from someone who learned the hard way. The preload is a funny thing. I just threw the parts in and buttoned it up because they fit. Now I'm dealing with low speed binding in my front end. If the preload is somehow adjustable, we need to find specs on what is the factory setting and try to duplicate it. I didn't know and am suffering the consequences. I am looking for a non fudged with 236 to swap out my frankencase with and then take my time rebuilding, paying attention to the preload.
A special clutch pack tool was mentioned. What is that and what does it do? Obviously I didn't use one so maybe that's the issue?
I will also take this opportunity to apologize to all for not having progressed on the wiring side of the 136-236 swap. Life has a way of getting in the way.

[racrx7]

The special tool is made by Kent Moore, J-44295. They can be had from eBay for a fraction of the cost of new. I'll post a pic of it set up for checking the preload in a day or two. It's an easy setup and check.

[photo_van]

one thing to watch when changing out inputs and planetary is the change in tooth cuts starting in '95. May not apply to the above TCs as I'm not sure when those came into production.

[Captn. Crunch]

What started out as a crazy thought in my head two or three years ago has come to see the light of day it appears. For those of you who have put up with my ramblings all this time I thank you. What looked like a long shot is turning out to be anything but. Congratulations to racrx7. You showed up with a van, a willingness to sift though all of the posts here and ask all the right questions. You did what I've been shooting for for awhile now and good job. Not gonna lie, I wish I had gotten mine to work first but hell we all get to benefit from racrx7's hard work and the addition of the np246 parts is just over the top stuff. A shout out to meggabuddys over on the zr2 site. He is hip deep in modding these clutched transfer cases and is doing four wheel smokeshows in his 600hp turbo'd zr2 blazer.
Hurry up with the wiring tutorial will ya. If I can't be first, seconds the next best thing! Once again good job =D>

[racrx7]

Thanks for the kind words CC And thanks for answering all my questions and sharing what you already had. You inspired me to take this all the way. Mega buddy also had good info and knowledge of the 236/246's inner workings. I just took all this and my years of experience as a mechanic and just put it all together. I'm also a bit of an electronics geek and that really helped to wire it all up as a functioning unit. I have been called meticulous and a perfectionist and tend to over do things at times, but the end results are usually something I'm not embarrassed to share. The good news is the wiring is not too terribly complicated and we can incorporate what we already have installed and wired up. We just add the missing circuits and of course, the required switch, and TCCM. GM has made it somewhat easier as we can use parts and electronics from both the Suburban and Blazer platforms to make the switch. For anyone considering this swap, I would suggest getting all the wiring harness with connectors from the donor vehicle. It will made the swap a lot easier and cleaner.

And CC, if there is anything I can do to assist you,( like set your clutch pack clearance), do not hesitate to give me a shout.

[Snowgeek]

Thank you all for your hard work on this. I am a decent mechanic but i will never be a front runner on this stuff. Awd is of huge importance to me so this swap gets me very excited

Considering I have a 2004 van, what vehicles (models and years) are considered the perfect donner for this swap to the np236? (I would wait on the 246 upgrades till down the road).

Thanks!!

Ryan

[racrx7]

The NP236 can be found in the 4x4 Chevy Balzers and S10's. The easiest way to tell if the donor vehicle has the 236 is to look at the selector switches on the dash. The 236 will have a 4 button switch, not the 3 button switch used on the 231 which do NOT have auto AWD capabilities. The years to look for are around 1997-2003. The later year the better. Get everything you can from the donor vehicle, wiring harnesses and TCCM. You'll be ahead of the game. As for the switch, I prefer the one that came in the 98-00 Suburbans. It just has easier mounting options over the S10-Blazer switches.
A new switch is available from Amazon, made by Dorman, for a reasonable price. The biggest part of this project is the wiring. Fortunately, GM makes it easier by letting us use some of the existing wiring and harness already in place in the van.

If you have any more questions, feel free to ask.
Good luck

Sent from Xfinity Connect Mobile App

[Snowgeek]

Great, Racrx7 my search has started!

Now another question.... Both you and c.c have modified the transfer case that you are currently running, but I gather that the np236 if pulled straight out of the blazer will fit and work in place of the np136 once all the wiring has been tackled. In other words the input/output splines are the same, bolt pattern and clocking are the same, and the stock astro drivelines are compatible.... Is that all correct?

I have recently read about 30 forums on 4 differant transfer cases and wanting to make sure I have my facts straight before spending hours in the mud at my local junk yard.

Do you have a build thread running yet?

Snowgeek

[racrx7]

Snowgeek,
If the 236 case comes from the vehicles I mentioned, (with 4.3L engine), it should be correct to go in your van. The cases of the 136 and 236 are identical. It's a direct swap including the brace that bolts to the left side. Shafts, speed sensors, case vent are a direct bolt up. No modifications required. As I mentioned, the wiring is the bulk of this swap. I haven't done a write up yet as work at the holidays have kept me busy. I'll also need to scan schematics and write notes as to what wires go where.

On a side note, I really like that camper roof on your van and want to do that to mine.