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Unread 01-13-2014, 09:24 AM   #1
StanF
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1995 YJ Wrangler 
 
Join Date: Feb 2013
Location: Austin, Texas
Posts: 865
Help with Tunnel Mod for larger Transfer Case

Background
I've got a larger TJ Rubicon 4:1 transfer case that I'm going to stick into my YJ very soon - like next weekend. It will require tunnel mods, which I've never done before. I'm looking for some help!

My old AX5/NP231 is out of the Jeep. And I'm sticking in an AX15/Rubicon case using an Advanced Adapters Kit and an AX5 bell housing.

Rubicon NV241OR Transfer Case:


I currently have a full flat tummy tuck, and would like to keep my skid plate as high as possible. Existing with NP231:


I'm pretty certain that I won't be able to keep my skid plate flat with the frame rails with the Rubicon Tcase, but I also don't want to go back to a 3" drop. Existing with NP231:


Problem
The front input of the Rubicon Tcase is about 1.5" taller than the NP231:


I am willing to cut the tub to get clearance, but that area of the tub is not easy to modify. There's a crossmember running right in that area that supports the tub/tunnel/front seat bolts.

Here's a shot with that crossmember sketched in:


And you can see it here (this is just a picture I found on the web):


I'm willing Cutting the tub for more clearance, but removing the middle section of that crossmember around the tunnel seems like a bad idea.

I'd like to keep the tunnel as "stock" as possible. I want to keep the fab to a minimum, while doing it right and strong.

Ideas
Option 1, which I don't particular like, is just to do a bump out behind the shifter.


Option 2 - just reshape the tunnel over the shifter area, so it blends easier. I think this will look the best, but would require a little more work/tub cutting. I've got it drawn out of scale - I'll need to be 1" to 1.5" over the existing tunnel.


I'd cut it something like this, and also reuse the existing shifter cover plate.:




Plan
1) The old transmission/Tcase are out, so the next step is to install the AX15 and Rubicon Case and see where to cut and how much.

2) I need to remove the seats and console.

3) I'll try to cutoff the existing tunnel in one piece, raise it as necessary, and fill in the sides and back with overlapping new steel that should be about 1" to 1.5" tall.

4) I'll make a cardboard template and fill in the front of the tunnel via Option 2.

5) Crossmember - most of it will remain in place since I am just raising the existing tunnel. I'll make cardboard templates and form/weld/fab some brackets to connect the cut crossmember on both the passenger and driver's side. This should keep it almost as strong as stock.

Feedback
If you can tell what I'm proposing, how does this sound? I've never modded a tunnel before, so any feedback would be much appreciated!

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Unread 01-29-2014, 01:17 PM   #2
babytank31
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1978 CJ5 
 
Join Date: Nov 2008
Location: nc
Posts: 149
Would a body lift help? I am not a big fan of body lifts but I would go that route before reconstructing a tunnel, just my two cents.
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Unread 01-29-2014, 02:23 PM   #3
StanF
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1995 YJ Wrangler 
 
Join Date: Feb 2013
Location: Austin, Texas
Posts: 865
Quote:
Originally Posted by babytank31 View Post
Would a body lift help? I am not a big fan of body lifts but I would go that route before reconstructing a tunnel, just my two cents.
Good comment - yes, I already have a 1" body lift.

I was able to get completely flat with the Rubicon Tcase. I ended up cutting some of the under-tub support structure, and also a fairly large chunk from underneath the driver's seat. Here's a picture after adding some sheetmetal pieces to fill in the hole. I will also need to modify the driver's seat frame.

As a side note for anyone who might stumble on this thread, I didn't clock the Rubicon Tcase at all. It seems to be clocked down less than the stock NP231, so using it stock worked fine.
img_3535-small-.jpg

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