Mitsubishi Transfer Case to Tera Low231 NP231 ...

Update: March 31, 2008 This weekend I finished fitting the block off plate for the doubler. Not a particularly complicated process but time consuming. The doubler goes to the shop Monday to get the block off plate welded in. I decided to leave the block off plate about 1/32 of an inch taller than the case so they can surface it down flush with the case half. The last thing I want to deal with are leaks after everything is assembled.

The 4340 steel from McMaster-Carr for the transmission to transfer case shaft showed up on Friday and I dropped it off at the machine shop on Saturday. I was impressed with the speedy delivery considering it was shipped ground form Illinois.

I also finished countersinking the three bolt holes in the doubler adapter plate. The support plate shown in the pictures wouldn't clear the bolt heads of the two lower bolts in the adapter plate and the bolt for the shift rod so I picked up a 1/2" and a 1" 90 degree countersink bit and three new hardened bolts from the hardware store. And, NEXT time I'll check the bolts BEFORE I buy them. I didn't think to check whether the adapter plate bolts were metric or not so of course I bought the wrong ones and had to make a second trip. The case bolts for my NP231 are metric.

The machine shop is ready to start on the shaft from the transmission to the doubler. That should be interesting. They're going to use an EDM machine to cut the splines for the end that fits the transmission output shaft. I'll have to get some pictures of the electrode once it's cut. I've never seen an EDM in action in person so this should be educational.:-)

A note for anyone wondering about the transfer case support and sandwiching it in between the doubler and the t-case. I came up with this idea after looking at several ideas tossed around on Pirate 4x4 and a few other forums. I wasn't real tickled with the idea of using the lower bolts of the doubler or t-case to attach a plate to especially since I couldn't find a way to use more than three bolts. That seemed like a lot of stress on the case half. I also couldn't figure out a good way to make the support clock-able. That was the big issue I had with all the other setups I found. If you later found you needed or wanted to re-clock the doubler or t-case you'd have to fab up a new mount. I have long since reached the point where I'm not interested in re-creating the wheel more than once.

So, after a little thought and a call to Duffy at D&D Machine, the maker of the Box4Rocks doubler, I decided to sandwich a plate between the doubler plate and the doubler clocking ring and then weld a foot on the bottom of the plate for a Jeep TJ transmission mount. The plate is cut with the same bolt pattern as the doubler plate so I can actually clock the support independently of the doubler and transfer case. The only drawback to this support design is it introduces another 3/16" between the doubler and transfer case. I wouldn't recommend this if the transfer case has the short input snout but since I'm using the Tera Low231 with the long snout I'll still have more spline contact area than if I were using the short snout transfer case without the plate. As I understand it, it's possible to swap the NP241 parts into the NP231 to get the longer snout or start with an NP231 with the longer snout in the first place. Either way it's not an issue for my setup and I'm not really worried about the loss of contact area given how little power is going to be going into it from the Mitsu 3.0L and the fact that I don't abuse the throttle when 'wheeling.