NP236/246 hybrid build

[racrx7]

So this is a NP236/246 4X4 transfer case build for my 03 AWD Astro. While I could have went with a 231 or 233, I liked the idea of retaining AWD while having 2HI, 4HI and 4Lo. It's all about choices. Several large GM products use the NP246 electronic controled TC that is called "select trac". So that's where my doner 246 came from, a 2000 Suburban, along with the TCCM, switch and all the related wiring that ties it all together. BUT, the 246 TC is not a direct bolt up to our vans transfer case adapter. It uses a 6 bolt mount while the 136 and 236 use a 5 bolt mounting pattern. BUT, the NP 236 case is a direct bolt up to the the TC adapter. In essence, you can just use the 236 unit as is and just wire in the electrics for it to operate. So why didn't I just go that route? Because the 246 internals are heavier duty than the 236 and 95% of those internals fit in the 236 case. (They should also fit in the original 136 case as the cases look identical). The 246 uses a 6 pinion planetary gear vs the 236 3 pinion. The 246 uses an 1 1/4" wide chain vs the 236's 1 inch chain. The 246 uses 10 clutch frictions to the 236's 8. Does the van need all that? Probably not, but it's nice to know it should hold up to anything it will go through. Plus, what fun is stock lol. Word of caution when building any clutch driven transfer cases. Do NOT use automatic transmission clutches in place of the ones designed specifically for transfer case use. They are spongy and have too much grip to slip when needed thus causing front axle binding. Ask me how I know lol. Pay the extra coin and get the GM frictions!! So enough talk, take a look at the pics of what I did. 236 and 246's tore apart.
thicker 246 chain vs 236/136 chain
6 pinion planetary vs 3 pinion. The front output shaft shown above the planetary on the right is from the 246 and will NOT fit in the 236/136 case. It uses different sized bearings not compatible with the 236/136 cases. That being said, the 246 rear case half cannot be used in conjunction with the 236/136 front case half.

[racrx7]

6 pinion planetary installed in the 236 case.

hi/lo range gear and fork installed.

clutch apply fork installed. Note the cam follower roller sitting on top of the cam. The cam is what's attached to the encoder motor mounted outside the case.

the parts on the right are the original clutch hub and clutch apply plate from the 246. These parts have been superseded with the parts on the left and offer improved strength and oil flow properties to the clutch pack. The new hub AND plate MUST be used in conjunction with each other and have specific part numbers for corresponding 236/136 and 246



The original ring on the left is from the 246 and the one on the right from a 236/136. Notice the shoulder on the one on the right? That takes up the space left by the fewer frictions and steels used on the 236/136.


The friction at the top is the oem while the bottom is an aftermarket that was sold as a transfer case friction. They are inferior to the oem and do not work well in our application! Notice the groves in the oem friction? This aids in oil flow across them and helps cool them.

[racrx7]

the oil passages in the main shaft may be partially obstructed due to machining processes. Looks like the splines were broached after the oil passages were drilled.





All oil passages were opened up with a small dremel bit and thoroughly flushed and blown out with compressed air.

[racrx7]

You can follow this link to read about the proper procedure for setting up the clutch pack clearance. This is paramount for proper operation, too tight causes binding and burned up clutches, too loose and not enough pressure applied to the clutches. In the case of the 236/246, the cam follower roller could fall off the end of the cam and prevent the clutches from releasing.

http://astrosafarivans.org/bb2/viewtopi ... 58&t=10162

[racrx7]

Can you tell which is which? The one on the right is the original NP 136, the one on the left is the built up 236/246 hybrid.



Hybrid 236/246 installed with actuator motor from 136 to test in AWD use. First test failed due to inferior clutches. Removed it, replaced clutches with OEM clutches, reset the clearances, reinstalled the TC and works perfect. No binding or "crow hopping" the encoder motor actuator for the 246 is now in place and is awaiting completion of all the wiring to be completed. I will do a write up upon completion and testing. But here's a couple teaser pics.
Cheers

[photo_van]

[mdmead]

Wow, nice!

[Stroverlander]

Excellent, looking forward to reading more!

[Astrophysics]

Fantastic!

[racrx7]

File comment: Or surface mount switch by slope plastic panel by drver right knee.

Yep, it's an option. Still haven't settled on anything definitive yet. Even thought of an overhead console mount if I can find a nice overhead console of some sort. Big sale at the local junk yard this weekend. Going shopping

[racrx7]

For anyone following this, I got my hybrid Select Trac wired up today and all ranges and modes work as intended by GM. As it's still up on the stands, I haven't road tested it yet, but I don't think the trans is shifting in 4Lo. But I also do not have circuit 1694 (4Lo signal), yet connected to the PCM. I'll try to post a short video of the ranges working when I get some daylight. I'll just need to find a permanent mount for the switch gear and tidy it all up. The bottom line is the 236 2speed transfer case will work in the Astro van and still maintain AWD. You'll also have 2 wheel high along with the other 4X4 ranges!
Cheers

[Captn. Crunch]

This might be of interest. And congratulations on your success!

When the truck is in 4lo, use the transfer case shifter switch to ground pin 16 (grey/black) on the main computer. Tells the computer it's in 4lo. This makes your transmission know, that your engine rpms should be 2.72 times higher than your driveshaft speed. Also makes the EPC solenoid produce higher pressure. Without this, you can burn up your clutches if you offroad often or hard. Read this thread. Miles from this site did this mod too.

http://www.txzr2.com...?showtopic=1993

[Astrophysics]

This is a wonderful product that could help all Astro Safai AWD enthusiasts.
Hopefully, you can prepare complete kit like instructions. Perhaps the Das Mule Expedition Outfitters in Washington state can pick up and run with your product to help commercialize it.
Or even Advance Adapters in Paso Robles, CA.
Keep up the good work.
Or even the T case rebuilder places may add this hybrid to their product offerings.
AP

[Astrophysics]

Or even Overland Vans could get involved to market the kit.

[racrx7]

This might be of interest. And congratulations on your success!

Thanks CC! I give thanks to you for the inspiration to see this thru. The link you posted didn't open for me, hmmm. The gry/blk wire from the TCCM, F7, is the 4wd Lo signal that goes to pin 16 on the PCM. I just haven't hooked it up yet. Hopefully that will let the transmission shift in 4lo.