Chevy & GMC Vans

This information was originally posted by BIGAT on the Astrosafari forum.

This is his documented swap of a NP233C electric shift 2 speed transfer case into his 1991 AWD Astro. This is a pieced together document so bear with me as I try to get all the information.





Transfer Case select switch with auto trans circuits.





Transfer case shift control switch and front axle switch.



Park/Neutral position switch ground input.

Continued...

TCCM power and grounds.



Transfer case module to encoder circuits.

Continued...

Parts needed from donor vehicle.







Now the wiring begins. This is where I will not have a lot of direction to go with. This can and will be updated once we get more info or sombody decides to take on the challenge!

Continued...

This is where BIGAT mounted the switches in his 1991 Astro.



Here are the two transfer cases side by side. The stock BW4472 is on the left and the donor NP233C is on the right.



NP233C on left and BW4472 on right.

Continued...

This post will document the installation of the 4x4 Posi-Lok front axle disconnect cable actuator. This is used in conjunction with the front diff out of the 95-96 S-10 Blazer that originally had a vacuum actuator. This system will allow the user to manually engage the front axle when in 4x4 mode or the front axle can be left unlocked to allow use of low range 2WD.







Location of the manual knob.



Cable attached to the axle disconnect.

Front axle mods continued...

This pic shows the difference between the stock passenger side front diff extension tube and the donor tube with axle disconnect.



These are a direct swap between the 91 Astro and 96 Blazer.



I am not sure why this pic was in the original thread other than to possibly show the diff being rebuilt.



One last thing noted...
"One other mod while front diff is apart. Remove @ .100" material from the spline end of the left side output shaft. There is a problem with the shaft hitting the diff. pin shaft causing a growling noise in 2wd that goes away in 4wd and changes with jounce and rebound of the front suspension while driving. Mostly noticed in '94-02 Blazers." - BIGAT

Wow that is a great set of info and photos!

I have a 2003 Astro AWD stock with the 3.43 axles and no locker.

I have been thinking of getting a 2 speed transfer case mod.

I saw one post saying I could swap out my stock NV136 case for a NP231 or NP241.
what is a good donor vehicle for the NP231 or 241? S10 Blazer?

Does any one have the full info and photos on this sway?

I want the electric dash mounted swithc for 4HI, vs 4 LO.
(ie. I do not want any extra levers on the floor.)

Can I get a AWD and still have a 2 speed transfer case?

I guess that means I have only 4 HI or 4 LO buttons to switch on dash??

I guess I am kinda getting ahead of myself, since I don't even have my 2 inch OV lift kit yet. but I would like the 4 LO range for driving slowly downhill.

I guess I can install aux tranny cooler and just shift to 2nd or 1st on the automatic tranny and select the Tow Haul mode to keep my speed low on steep downhills.

thanks for any ideas

Astrophysics

I guess I missed the repost of this. You rock Dean!

Astrophysics, you can't use a 231 or 241 if you want electric shift. You will need a 233 or 243 as they are the electric shift. Then you can just follow this thread for the install.

Thanks for the info on the use of electric shifter 2 speed T Case, 233 or 243 to swap out my OEM T case in my 2003 AWD Astro. I only have 80,000 or so on the Astro and I will probably wait til I have tranny or T case trouble to do the mod.

***************************

thanks again,

Astrophysics

Hi, Im new to the board but have been lurking for awhile now.
Thanks for the great info in this thread!
I do have a few questions though.

On my 91 AWD I want to do the front axle disconnect and plan to install the PosiLok. Can I use my factory front diff and just add the the front axle tube from an S10 like this:

Would I need more parts besides this tube? OR do I need to swap out my diff for an S10 Diff? And do I need the actual S10 axle? And FWIW, I plan on doing a gearing change.

Second: I am going to install a 231C and use a GMC Suburban floor shifter I have. I am curious about the speedo connection that the TC has. Should I be able to just plug in my connection that is on my Astro now? Here are the specs on the tags of the 2 different TCs I have found for sale.

1)Ident: 15964731
Ident: JZ
Ident: LK
Ident: MR
New Process 231C
Slip-on yoke.

2) Ident: 15675127
Ident: HC
Ident: HT
Ident: JS
New Process 231C
Electronically driven speedo. incorporated with anti-lock brakes.

Im not sure how to really read them, possibly you can help. I know that I am looking for the 231C and should get one that has a 27 rear spline so I can just reinstall my driveshaft without modifications.

Lastly: I am going to go with 31X10.50 tires and an overland lift and want to switch out the gearing in the diffs to 4:11 from what I believe is 3:42 ratio right now. Any thoughts on the 4:11 gears with 31's? All the research I have done say this should be an ideal gear size for power and cruising with the auto OD tranny and 31's

I have and endless amount of other questions about my planned 5" OV lift kit and related items like if its necessary to swap out the older style torsion bars, or opinions on different after market shocks, but will save them up for some reply posts.

THANKS in advance for any input!

Is this the thread for me and my '03 AWD? I need to install a 2spd T case with an electric switch in the next month or so so I can go on this trip with these ole boys.

http://forum.pnwadventures.com/showthre ... 469&page=6

Do I use the same T case and the same recipe? Drive shaft?

If I do this swap on my '02, what do i do with the front and rear drive shaft speed sensors? Do I need to do the 2" body lift kit like the manual transfer case conversion?

Can anyone explain to me how the front differential with the locking mechanism works?

Thanks!
Peppy!

Time to do some reading...Posi-Lok