Well this whole crazy thing started when I started researching the similarities between the Jeep AW4 and the Mitsubishi V4AW3 transmissions. I kept my eyes open and found an NP231 from a 2001 Wrangler with a Slip Yoke Eliminator (SYE) already installed. I also found an AW4 tailhousing from an unknown year Cherokee.


My first steps were back in December when I tried mounting the AW4 tailhousing and np231 to the V4AW3. The tailhousing bolted up just fine and the splines ended up being the same size and count. This initial "test fit" did let me know that if I wanted this to work I would need a "short" input shaft for the NP231. Over the years NP231's have come with different input shafts varying in spline count and lenth. There are three lengths and two spline counts: 21 and 23 splines. The V4AW3 is a 23 spline tailshaft. I also used this opportunity to check the clearances with the floor, exhaust, crossmembers, and t-bars. I felt confident that the NP231 was a good fit and at the most would need minor clocking. After this wrenching session, I reinstalled the Active-trac t-case so I could continue driving the truck while I shopped around for more parts. I would recommend messing with the Active-trac t-case as little as possible! It is a heavy beast <img src="/forums/images/graemlins/oink.gif" alt="" /> to bench press into place <img src="/forums/images/graemlins/shiner.gif" alt="" />.

Since I first started dreaming of this mod, I knew that I wanted to make a dual transfer case setup. I felt that the dual case provided the following benefits:
1)Allowed for selectable ranges, ie:1:1, 2.72:1, & 7.4:1. With these options, even the middle speed is lower than the stock 1.90:1!
2)It was something I could piece together as time and money permitted.

I had three options to choose from in trying to create a dual NP231:
1)Build the components myself. I didn't like this option simply because I knew it meant welding a mid-shaft together. I wasn't crazy out a welded shaft being in the heart of my drivetrain. <img src="/forums/images/graemlins/shiner.gif" alt="" />
2)A Mad Rooster Offroad crawlerbox
3)Or a D.D.Machine "Box4rocks"
I decided on the D.D.Machine kit. I chose this kit because the guy that makes them seemed to really stand behind his product and know what he was doing. Also this kit had provisions for oil filling and draining. I was also less than thrilled with how the Mad Rooster guy handled himself when answering an email of mine. <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

I was lucky enough to find a Box4rocks 23 spline kit second-hand that had not yet been installed and came with all the parts that would be needed from a donor NP231 to make the doubler. I got even luckier when I found out that this doubler donor was a 23 spline short input shaft!
Here are some pics of the Box4rocks and doubler parts:
The doubler cut, welded, and guts assembled (you can see the midshaft poking out in the middle):

The plate that seals the rear of the doubler:

The clocking ring:


More to come... <img src="/forums/images/graemlins/kewl.gif" alt="" />