Because of my frustration and distrust with the NP233 transfer case and it's fellow electronic components that have reached the end of their life, I have decided to swap to the NP231 transfer case found in manually-shifted S trucks and a few other makes and models. I also plan on setting up some type of posi-lock cable, but that won't come 'til later.

I'm going to be keeping track of my build as I go. I plan on using a stock shifter from a blazer since there are a few in the junkyard, and I already have my t-case. It came with my Jimmy when I bought it. I suppose the previous owner had the same thing in mind.

So far I've just got the case out of the truck, and I put them side by side to compare. As far as case removal, it's pretty straight forward. Only thing that really held me up was the constant dripping of ATF (needing to tend to it) and the fuel line clamp at the very top of the T-case.



OK, so besides the obvious length difference in the tailshaft, there are actually quite a few differences. This is not a direct bolt in swap. The 231 I have is for a gear driven speedometer cable, while the 233 from my '94 uses a Vehicle Speed Sensor. Also, it can't be seen in the picture, but my current driveshaft will not work with the output shaft of the 231 the way it sits. The output shaft is too small on the 231. So, at the very least I'll have to swap the output shaft with the housing and the vehicle speed sensor stuff. I'll take pictures as I go.

The empty spot where my transfer case used to be

 

So I got things switched around and I've ended up with two frankencases. The one i'm using is on the right, all sealed up and ready to go, and shifts nicely. The 231 seems like it was rebuilt before I took it apart. It had a 'parts washer' smell on the inside and there was no ATF to be found. The NP233 is just sort of pieced together so I know where all the parts are just in case. Now I need to figure out how i'm shifting this thing. I'm gonna take a trip to the junkyard in the next few days and pull a shifter and stuff.




Both shafts together trying to show off the diameter difference although you can't really see it right here. There is a significant difference in the length as well, and it doesn't look like a mechanical speedo shaft could be adapted for a vehicle speed sensor. There is an extra snap ring groove required.


NP231 after putting in the donor tailshaft

 

it's lookin' good so far.

i'm with ya on wanting a manually shifted t-case, works much quicker, and you never need to worry about that damn TCCM, which i just had to replace in my '98-yay wreckers!

i was thinking about doing the same thing as you are, when i get around to swapping in my 5 spd, so i'll be following along with your build quite closely.

 

Hey, I'm on board too. Better you than me for the test case though. So what did you do about the VSS? Just use the tailshaft from the 233? That's what it looks like. I guess all the parts will fit OK since you seem to have a working (can we call it a 232 LOL) t-case.

 

shouldn't we add "BF" to the begining of that model #, making it a "BF232" t-case?

 

Maybe I'll make up a special tag for the back of the case lol


I basically swapped over the whole rear half of the 233. Once I had the shaft swapped it's pretty straight forward. The ring for the sensor looks like a gear that is held on with an extra snap ring. Then add the correct housing with the sensor and its good to go. I didn't even have to pull the sensor from the housing in the process.

 

Yeah. The rear half of the t-case is pretty easy. All of the hard stuff is up front. I had my rear case apart to reseal everything. So the mainshaft diameters are the same? Looks like it with the chain fitting as well as it does. Which chain did you use? I don't think you're going to have to worry about a rear driveshaft length problem. Looks like you can just use your original. Cool. Have you anticipated any computer problems since I don't think any of the older stuff was controlled by a computer. You know, fault codes, etc. I guess the only thing now to tie into an ECM is the VSS.

 

The mainshaft diameters are the same on the whole shaft except for where the slip yoke will go...the tailshaft part. The manual case had a smaller end to accept a smaller slip yoke. Also, the slip yoke wouldn't even fit into the manual case's tailshaft housing since it was too big. I measured the shaft where it would sit in the shift collar and in the planetary gearset with a digital caliper and everything is the same. No weird end play when its all together or anything like that. I imagine they built the 231 in 1994 to accept a VSS since I think a '94 wouldnt have a speedo cable regardless of manual/automatic shifting. Bet it looked just like this. I probably just got unlucky and ended up with an older version so I had to swap things over.

The length of the 231 should be unchanged from that of the 233 now that I have all the new stuff, so I'm certain the driveshafts will work as they did. I don't forsee any computer problems since the VSS should work just like it did as well. Only thing is the computer will never recognize when the truck is in 4x4. I'll probably pull the fuse for the TCCM just so it doesn't turn on and flip out when it realizes there is nothing plugged into the transfer case harness.

I used the chain from the 231, but I don't think it would matter anyway. Just happened to be the one I picked up. They both looked pretty good. I'll probably keep the 233 around just in case I break something in mine. Most of the parts would swap over

 

that's odd.

when i found this.......





on my youngst brother's '94 Jimmy last year, i just took the drive shaft from a '98 i had stripped, and she went in, no problem.

maybe you're right, someone could've swapped the t-case before (for whatever reason).

thanks for the insight, another good thing to watch out for when i get around to mine. kinda wishing i didn't scrap all of those manual t-cases i had.

 

Picked up my stuff to shift the thing. I still need one more bracket that bolts to the transmission to hold the shifter, but I think i'm going to try to make that bracket. It was just impossible to remove that bracket without dropping the trans of the donor vehicle. Looks like everything will fit fine, I just need to make that one bracket or find one, and cut the hole in the floor for the shifter, then screw down the shift boot with the self tapping screws. Also where my two bolts need to go my transmission does not have threaded holes. Guess i'll have to make the threads or come up with something totally outside the box for this one.




Those 2 bolt holes that line up vertically is where I need to put the bracket, and then figure out where the through-bolt for the shifter should be at so everything lines up ok.



My console dyed black using interior dye. If you haven't guessed already the truck is black on black so this will look pretty good once its all together I think.