Nobody has done an NP236 swap yet, right? Will it fit?

[Herbie]

Hello all. Among my first projects for my new Astro is the 2-speed transfer case swap. I like the idea of keeping an AWD option, so I found a line on an NP236 transfer case. However, from looking at the pictures and comparing to an NP233, it seems like the case itself is a bit bigger in a couple of dimensions.

Can anyone confirm if it should REALLY fit?

I'll attempt to attach a couple of comparison pictures:

NP233:


NP236:


In particular, it looks like the mounting surface for the front driveshaft is a bit further forward. The coupling is obviously different. Some sort of face mount instead of the spline? Also the extra stiffening ribs around the output side might cause interference also.

This stuff is a decent price, but not "cheap", so I don't want to buy it and ship it if there isn't a reasonable chance it will fit. Should I just punt and give up on AWD and just go NP233?

[GnarliSafari]

well, as some of the members have proved, anything will fit it just depends on your fabrication skills, time and patience. if you are looking for a direct bolt on, probably not, but if have the skills it is doable.

[Herbie]

Yes, bolt-in (ish) would be preferred. I'm prepared to notch the cross member, but it would be nice if everything else was bolt together.

Along those lines I'm still a little confused on what the interchange circumstances are where some people can reuse the OE driveshafts and some people have to modify driveshafts...

Another strike against the NP236 (or 4-button 4x4 as the Blazer guys seem to be calling it) is that it seems like there are a lot of issues with the TCCM in that setup. Lots of threads on how to diagnose problems and getting hold of a "4-button TCCM" seems to be a lot harder.

Not looking to re-invent the wheel here, maybe I'll just stick to tried and true.

[lockdoc]

If you are in SoCal and plan to off road only then I would stick to the 232 or 233. If you plan on driving in the snow like I do in the northeast I would really like to see if the 236 would work out. Me and some others have found that 232-233 does not work as well in the snow like the AWD did.

[Herbie]

If you are in SoCal and plan to off road only then I would stick to the 232 or 233. If you plan on driving in the snow like I do in the northeast I would really like to see if the 236 would work out. Me and some others have found that 232-233 does not work as well in the snow like the AWD did.

Yeah, that's why I was looking into the 236. I'm a major AWD booster (long time Subaru owner), and have enjoyed the benefits of AWD in heavy rain and the occasional skiing trip. If possible I'd love to keep the option, but I want to make sure it'll work.

As a side-note to the AWD question, I should point out the following option for a rebuilt/exchange/upgrade from drivetrain.com:
136GM to NP231 upgrade

Clicking that upgrade gives this bit of text: "Replacement Upgrade replace your 136GM full time transfer case with our modified NP231 you will now part time all-wheel-drive with low range, modifications will a different front output shaft , you supply linkage. Your cost on this unit is $905.00 plus $250.00 core deposit plus the freight. "

It seems like you might be able to have a best of both worlds arrangement with part-time AWD and a manually selectable low-range. Its not cheap by itself, but since that's about the same price as a rebuilt transfer case on exchange, it isn't too bad a price if you have a high-miles unit that needs attention. Since my van has only 52k miles and many of the donor units I might pull parts from to swap are 150k+, I might opt for a rebuild anyway, just to be safe, and this saves me the purchase price of the donor TC since I could use my existing unit in exchange.

I've contacted them for clarification to see what exactly the option entails. If it includes a fully locked 4WD mode like AWD,4HI,4Low, then it sounds like a winner for a lot of people. If its just AWD-Hi, AWD-Low, (like the 2-speed Subarus from Australia), then it won't be so hot for offroading unless you just need to slow things down.

This seems great if you live in snow country and don't want to lose your AWD but still want to have a crawler gear. For me here in SoCal, having an AWD option would be nice for the occasional trip to snow country, but I'm hoping I might see a little bit of a mileage boost from having a 2HI mode, so if I had to choose between that or AWD, I'd choose the more conventional 2HI/4HI/4Lo arrangement.

[lockdoc]

What makes the AWD so desirable to me over the 4WD tcase is the viscous coupling in the AWD for the front diff. That slippage or clutching action prevents the jerking you get at the front wheels with the direct connection of the 4WD tcase. Which in turn makes driving in the snow much more pleasurable. I used my AWD tcase in the woods many times before I went 4WD. It worked great but you burn the trans and brakes terribly not having a low range.

[LiftedAWDAstro]

The driveshafts will need to be modified. The Trailblazers use the same front diff so a front shaft will be easy. The rear you will need the correct slip yoke and a conversion u-joint to connect to the stock rear shaft. You may need to shorted/lengthen the rear drive shaft though.

Before you attempt this mod, do the 4" lift so you have the clearance between the tranny crossmember and body. The transfer case should bolt up to the 4L60E with no issues. The wiring will be basically the same as with the NP233 swap. You will need the correct switch, TCCM and wiring. Also get the donor vehicle wiring diagrams.

I agree with Lockdoc. The NP236 swap would be ideal for us in the snowbelt. Some of us have experienced a very darty front end while in 4WD Hi. I have no idea why these vans do it as the S-10's don't.

[gabequest]

Ditto on the "scary" darting with 4WD. My NP231C lets me crawl something fierce, esp with my V8, but I'm definitely disappointed about the scare-factor in snow. It would be awesome for you to figure out this swap and post the "how to". Low range AWD would pull these vans through pretty much anything we need it to, esp with the gov-lock option.

[Herbie]

OK, two small follow ups:

First, on the Drivetrain.com 136GM to NP231 "upgrade": I heard back from them, its basically an exchange program. You send in your 136GM as a core, they return an NP231 with the correct yolkes, etc. for your application. You provide your own shift linkage.
Might be a worthwhile option for anyone who wants a manual shift and would be paying for a rebuild anyway, since this allows you to use your AWD case as the core for basically the same price (and you don't have to find an NP231 to rebuild).

Second: Looks like the sticking point on the NP236 swap is going to be finding a working TCCM. Everyone I've talked to that has the parts always has everything BUT the TCCM. Apparently these are always snapped up right away as they are frequently needed to replace failing modules.

That right there is enough to make me back away slowly for my personal project. I'd love to pioneer this for the benefit of the group, but since I don't absolutely need the AWD function, its not worth it for me to make the project harder, especially by going out of my way to find a part that seems to fail frequently.

So, with that, I think I'm going to bail on the NP236 and just try to find a nice low-miles NP1 S10 with an NP233 I can pillage.

[mdmead]

There *might* be one other option. Early Grand Cherokees... and XJ's I'm sure... offered a full-time (AWD) with the ability to lock with 4-lo and 4-hi. These were non-electronic units, so probably used a viscous clutch. The question is can one adapt it to a 4L60E or find an adaptor to do so. I don't recall the T-case number, but Dean might as I've brought this up before and I recall him offering up some info.

[LiftedAWDAstro]

A NP242 transfer case gives you 2WD, 4WD part time, 4WD full time, Neutral and 4LOW. I imagine Advance Adapters has something that will work. Pricey though.

[MountainManJoe]

What about the NVG 246 ?
It should operate like the Astro AWD but with 2 speeds and it should be stronger than the 136/236.