How to wire up a NP 236 in place of a 136.

[MountainManJoe]

this site sucks

I try my best to make it not suck, so if you have any suggestions I'm all ears.

and you can’t upload photos.

You can . No idea what's stopping you.

[MountainManJoe]

I DID notice the front prop shaft sensor shows about 100rpm higher than rear with the front axle disconnected and I think that is weird

under what conditions? I think the 236 senses an RPM difference between front and rear axles (same as the 136, difference must be greater than some threshold because front versus rear prop shaft speeds are different during an ordinary turn maneuvre). I'm sure it's explained in the service manual "description of operation". If the front axle is disconnected then speed difference will rise unchecked. (possibly even burning out the shift motor). Probably should connect the axle.

[tanvanmanwithaplan]

I figured out the image thing I am just dumb. Phpbb is just old school lol I am used to the new fangled bulletin board image upload dialog

Here’s the wiring diagram for the Tahoe switch

The front prop spins freely at the same speed roughly as rear in 2wd mode with no driveshaft I am guessing due to friction from clutch preload. I don’t see it being much different than having a blazer differential with the axle disconnect on. And I don’t see how it could spin faster than the transmission that is driving it so my wild guess is it is a calibration thing they did in the tccm or maybe on the reluctor wheel itself so the front is always a little faster so the clutches don’t engage too soon. Just a guess.


It’s a few rpm maybe 10 or so at low speeds once you get going 20 or more I see about 100rpm higher across the board. I guess I’ll see if it’s still showing higher once the driveshaft is back in.

[Roadstar01]

Great information cuz I'm actually using that as part of my build today or for the next couple weeks I hope to be done with my upgrade from 136 to a np246 transfer case so I'm hoping that what you are talking of the 236 wiring will be the same for the 246 transfer case as well? I did pull all of the trans wiring harness from the donor 2001 GMC Sierra 1500. So I'm hoping that's the case that the wiring will be the same solution.
can you tell me if I can follow your instructions for my build as well on the 246? Thanks Much!

[MountainManJoe]

As far as I know, the 246 is just a heavier built 236. Wiring should be the same.

[Roadstar01]

Thanks
I am just in the beginning of peeling open this onion LOL. But if the wire harness is the same will be a lot of help following the information I'm finding on what wires I will need from the donor transmission wire harness for the 246.

[tanvanmanwithaplan]

The VSS and rear prop shaft sensors are reversed from 236 to 246.

You also can’t bolt the 246 on the Astro van is what I’ve heard but I never actually tried it.

There’s really no reason to use the entire 246 wiring harness, you just need to add wires for the encoder motor and switch. You can chop pieces of the 246 harness for that though if they fit!

[MountainManJoe]

There you go. We are blessed here to have members with hands on experience with this stuff.
It makes sense because Blazers and Jimmys had the 4.3 whereas 'Burbs and Hoe's have 5.3's and 6.0's . Heavier built like I said, which likely means different bolt pattern.
Anyway you can get electrical schematics for all that kind of stuff on the website charm.li
Fantastic resource that is.

[Roadstar01]

I'm actually in the middle of searching for transmission and transfer case wiring schematics for a 2001 Chevy Sierra 4x4 of course and the same wiring harness schematics for my 2001 GMC Safari AWD.

[tanvanmanwithaplan]

The wiring might work the same but the vss and rear prop shaft sensor positions are reversed between the 4.3 and v8 application auto track 2.

136/236 layout:

246 layout:

IMG_2931.gif (53.49 KiB) Viewed 1254 times

Just use the Astro wiring harness w the 236, follow the PDF earlier in this thread, and if you’re using the Tahoe switch follow my switch pinout.

The 246 tccm MIGHT work but why even mess with it when the blazer one is known to work and are super plentiful and $30 at pick n pull. Buddy’s u pull in Springfield mo had 8 cars I found with that transfer case.


You CAN put some of the heavier duty inter als fro
The 246 into the 236.

[Roadstar01]

I chose to go with a 246 because the Safari as we know only had a 136 all-wheel drive so I'm hoping following your instructions and pinout lessons learned will apply to the 246 as well. And then I can also with a 246 use the optimum power from the LS 5.3 I have in the Safari now

[tanvanmanwithaplan]

Do you have the transmission that came with the 5.3 in the van or the one from the 4.3? The output tail bolt pattern is different.

[Roadstar01]

I am waiting for the transmission to be built with heavy duty billet components etc. I did receive the tail shaft housing from the donor when I pulled the 246tc. It is about a half inch longer so I am hoping there's enough play in the slip yoke of the rear drive shaft to slide in enough with space allowing the rear differential to travel up and down.
As for the front I have to use the front drive shaft from the donor since it is a female line output on the 246. My Hope is I will just have it cut to length As for the four bolt flat flange I will separate it at the u-joint and install it onto the drive shaft from the donor vehicle. But yes I told them the transmission is for a 2001 GMC Sierra 1500 4x4.
Am I missing any thing or miscalculating anything for the solution?