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

[Herbie]

Manual shift TC makes more sense if you don't have the clutch controlled AWD as an option, but if the NP236 swap had been this well documented when I'd been doing my conversion so many years ago, I'd probably have taken that route.

I would also consider electronic 3 button swap... Encoder motors are easy to replace and cheaper than the linkage kit in either case if it does fail.

Nearly every 4wd vehicle made in the 21st century uses encoder motors. But hey if you want a lever more power to ya. If I had a linkage set up already I would just keep on using it.

I should have been clearer - a manual shifter for the TC makes sense only in the cases when you don't have AWD on the table. If you currently own an NP233, you have a choice to make. I went manual-shift because LiftedAWDAstro had already done the conversion work when I bought his TC, but he also supplied all the electronics stuff, so I might have opted for the 3-button solution if I'd been so inclined. If he or someone else had been selling a complete NP231 "kit" at the time I was buying, I'd have considered that too, because the NP236 swap wasn't a "solved problem" yet.

If you have access to an NP236 and the skills to deal with the electrical installation, then a manual shifter makes zero sense. If I were starting from scratch on a van today, that'd definitely be my choice - it's really the best of all worlds.

[racrx7]

Been a minute or two since I last visited this thread, but glad to see there’s still interest in the conversion. Congrats to anyone that has been successful with the conversion. Mine has been trouble free since the conversion and have since installed an S10 front axle with axle disconnect. I use a manual cable to engage the front axle vs the original S10 vacuum actuator.
Cheers!

[tanvanmanwithaplan]

My service awd light comes on if I use the AWD and sometimes in 4hi after wheeling for a while in rough terrain. At that point it is stuck in whatever mode the xfer case is in. Anyone else seen this? The 4wd is definitely working.

[Astrophysics]

Hi,

I have np231 c with manual cable shift.

Did you try going a few feet in reverse to unload the axles and t case after agressive wheeling?

AP

[Snowgeek]

Been a minute or two since I last visited this thread, but glad to see there’s still interest in the conversion. Congrats to anyone that has been successful with the conversion. Mine has been trouble free since the conversion and have since installed an S10 front axle with axle disconnect. I use a manual cable to engage the front axle vs the original S10 vacuum actuator.
Cheers!

racrx7: I am in the same boat. No hiccups what so ever. I too installed the S10 axle and cable actuated disconnect. Where did you locate your cable? I will be honest that I still have mine posi-lok tucked in the engine bay because I can't find a spot that i like it. I have quite liked having the option of 2wd low in a host of towing situations.

Snowgeek

[Snowgeek]

My service awd light comes on if I use the AWD and sometimes in 4hi after wheeling for a while in rough terrain. At that point it is stuck in whatever mode the xfer case is in. Anyone else seen this? The 4wd is definitely working.

Ok little more information might be helpful. It seems that when you say "stuck in whatever mode" that it has happened multiple times in multiple settings? What is the time between when it happens (light goes on and seems stuck) and when the light goes out and you are able to switch modes?

Astrophysics, has a point on the "move the van back a forth a bit" but if the case was under tension the shift typically just stalls out and goes back to the setting it was in and then you try again..... it shouldn't flash a warning light at you.

If I were to guess (not sure it's educated..... but it might me a place to start) I am thinking you have a problem with the encoder motor or you have a short or loose wire in your installed wiring harness. Warning: as far as I know pulling out the encoder motor and operating it to check for function will blow up the device..... not sure of best ways to test this. I have a spare of every part I installed because the are cheap to have around for testing issues such as this. As far as wiring I would be checking all the connections first before diving into checking each wire for connectivity..... this could be goose chase.

There are many here that know much more than I do and hopefully someone will chime in with more information and experience.

Ryan

[tanvanmanwithaplan]

I think theres a speed sensor or wire wire or something that isn't acting right for some reason. It does it after you wheel for a while and then is fine again once you restart.

So--My random guess is the TCCM is not getting what it expects in some scenario and then erroring out. I think I would need to plug it into a better computer during when its having the issue to get to the bottom of it. but it's not enough of an issue for me to care to, tbh.

[tanvanmanwithaplan]

Update: I never swapped in the s10 axle tube w disconnect. After about 3 years the transfer case is binding in turns in 2hi. Never did get the AWD to work reliably. Maybe I did something wrong or got bad junkyard parts. I also didn’t really use the 4wd terribly often so I’d say most of the wear that lead to failure was in 2hi. Definitely happened many miles after I had some multiple flat situations and drove a long ways with mismatched tires.

After this experience I believe the axle disconnect is a necessary feature if you want to do the 236.

Does anyone know if the 236 tccm and button and wiring will work on a 233 if I just don’t push the awd button ever?

[tanvanmanwithaplan]

I finally got around to pulling the codes out of the TCCM. Using an obdlink LX and torque pro in raw terminal mode

>19 d2 ff 00.
6CF11A594300114B C0300 "Rear Prop Shaft Circuit Malfunction"
6CF11A594374114D C0374 heat or general fault
6CF11A59A72511C9 B2725 switch fault
6CF11A59000093BB - end of faults

The switch fault was from driving around with the switch unplugged.

I ordered a new rear prop shaft sensor and will report back once I have that fixed. The transfer case also started binding on turns in 2wd just like the 136 used to if you ended up running mismatched tire sizes (long story but I double flatted in Montana. I have the front driveshaft out and just flushed the fluid. I am going to put new tires on it, put the driveshaft back in, and then flush the fluid and hope the binding goes away. I really wish I had done the axle disconnect but it’s such a pita to pull the cv axles… I also need an oil pan gasket and this is all starting to feel like it’s more work than it’s worth lol

[WoodButcher]

After the fluid flush there is something about doing figure 8's in a parking lot, I don't remember what or why as I have not needed this yet but you will want to look into it.

[tanvanmanwithaplan]

Not that anyone asked, but I put a new speed sensor into the rear propshaft and it's still giving me grief. Also tried swapping the front out in case it was just a speed mismatch issue. No dice

Going to get the meter out and check the wiring as well as make sure I pinned everything correctly back in '21 after I am done with my ECU pwered eFan conversion.

I also am going to try to use my new Tech2Win interface to update the firmware on the TCCM. I belive there is a TSB on updating the TCCM resolving a C0374 and it's worth a try

[tanvanmanwithaplan]

Update: I got a VXDiag VCX Nano to use with PCMHammer to flash my 0411 PCM for eFan mod and decided to try out the Tech2 function...

tccm.png (51.84 KiB) Viewed 273 times

Replacing the sensor didn't work. Just verified I am not getting rear propshaft speed at the TCCM so time to ohm out the wire. This is actually great because it gives me something specific to look for. Excited to have AWD again.

Side note: This Tech2 thing is amazing. Definitely worth $100 if you're going to be working on any GM vehicle. It's way better than the OBDLink and Torque Pro to be able to talk to all the modules, etc.

[MountainManJoe]

The tech2 is very capable hardware. Well worth the money. Unfortunately the interface is really primitive. The graphs are almost unusable. the Chinese knock-offs tend to be pretty flakey too.

Don't forget in Tech2Win, go to the Windows menu > Tech2Win Data Display. It lets you view a lot more data at once in a nicer more modern format.

[tanvanmanwithaplan]

Update I found my issue. It was not wiring or a bad sensor, I believe it is faulty junkyard TCCM. The TCCM can not read speed from rear prop shaft sensor pins even when I swapped the working front speed shaft pins over. I am going to try the updated 12577412 TCCM which apparently has software and hardware updates vs this one.

Here's what all I had to do for diagnostics. I am going to be honest if I didn't go to engineering school and have experience with controls and wiring this would have been (more) of a nightmare or impossible. https://www.astrosafari.com/threads/rea ... cs.152527/

Kind of relieved it wasn't something I did wrong installing (other than not know I should get a later model TCCM) but also frustrating to do all this work over multiple years

[tanvanmanwithaplan]

I got a junkyard TCCM today and put it in and tech2 showed rear prop shaft rpms right away and I drove all the way home with AWD enabled (no drive shaft in right now) w no svc awd light, so good to go I think

I wired in the 03-06 Tahoe switch (the one with the long connectors, not the blue) last night and it works, you can see the wiring guide I made for it on the topic np136 to np236, this site sucks and you can’t upload photos.

Still have some taping/wire management and buttoning to do and putting the tccm back into its coffin , then install the driveshaft and hit some figure 8s and change the fluid.

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…. Also I was thinking about it and for the 136 vans if you have mismatched tires as long as you put the larger ones on the front it shouldn’t cause any binding bc the clutches attach when you have a front lower than rear situation… I don’t think I’ve every read that take before, wish I had known that 10 years ago