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AW-4 Transmission Swap

T-Day (tranny install day) was sitting at T minus 6 and counting.  I had made a checklist of things I needed to do before I put the TJ on the hoist for the actual swap.  One by one, I was getting them checked off.  I found myself with a bit of spare time so I decided it was time to clock the transfer case.  I had helped ScottK re-clock his and wanted to get it out of the way before the swap was underway.  The details are a little foggy from doing Scott's, but I remember that we measured a LOT before drilling the holes.  I think we made a paper template and then transferred the hole locations onto the AW4 mounting surface using a center punch.  We had to use a round file on a couple of the holes to get all six bolts to properly fit, but it worked out just fine.

Update 01/22/2013: I found out today while talking with a friend that Iron Rock Offroad now sells a drilling jig for $45 that will allow you to drill your holes properly the first time.  You can find it here

I lucked out when it came time to drill the holes in my AW4.  I had told Troy about having to re-clock the t-case when we were first telling him about the tranny swap.  He got a big smile on his face and went over to one of the storage racks in the shop.


When he returned, he was holding an Advance Adapters spacer, part # 51-0404, made for a 4L60/Dana 300 combination.  (The 4L60 is essentially a 700R-4 auto tranny.)   Don't even ask me why the hole pattern in the spacer actually fits that of my NP-231 transfer case, nor can I answer the question as to the spacer exactly fitting the recessed area of the AW-4.  But suffice it to say that I was very glad to see that it did.  I had at my disposal a "template" that was about 1" thick and was a perfect match for the hole pattern I needed to transfer to the AW-4.  It just don't get any easier than this! 


If you are going to do it, you might as well do it right the first time around.  I grabbed a set of transfer bunches from the tool locker and found one that just slipped through the spacer's hole.  Transfer punches perform the same function as a regular center punch except that the body diameter of the punch is constant from one end to the other.  There is a little tit on the bottom that actually does the marking/punching. 


I made a pair of alignment marks on the AW-4 so I could determine proper placement once the spacer was put into place.  The mark on the left indicates the centerline of where I want the new hole to appear.  I only had to mark one hole since the spacer plate would located the remaining five holes correctly.  You can see the mark on the edge of the spacer (top of photo) indicating the centerline of the hole.


With the mark on the spacer aligned with the new hole mark on the AW-4, it was very easy to gently tap the transfer punch to mark the exact center for the 6 new holes.  I used a small C-clamp to keep the spacer from moving as I was marking the holes (sorry, forgot to take a picture of it clamped in place).

With six nice newly marked holes properly located on the AW-4, I was down to the final step....drilling the holes.

At this point, I had two options available.  I could unbolt the adapter housing from the back of the the AW-4 (which was what the 6 holes were just marked on).  ScottK did this (you can see it here) and it worked just fine.  Doing it in this manner should pretty much guarantee you that your holes are perpendicular and go straight through since you can put the adapter housing on the drill press table.  When you are done drilling the holes in the adapter housing, you will need to reseal it when you bolt it back up to the transmission housing. 

I opted for the second option, which was to drill it free hand (no help from a drill press).  If you suck at this, you probably want to remove the adapter housing and use the drill press. 


Prior to drilling, I took several heavy paper shop towels and packed them around the output shaft.  Since the adapter housing was not being removed, I knew there would be metal filings all over the place before I was done.  I did NOT want them down in the seal area.


The small hole in the above photo is the pilot hole I made first.  I didn't want to attempt the full size hole from scratch.  I find it easier to control the smaller drill bit and then step up the hole size to the final dimension.  In fact, I used three drill sizes when making these holes.  The final drill size was 13/32", just 1/32" larger than the 3/8" studs on the transfer case.  That didn't leave me much room for error (or clearance) but I figured I could bump the hole size to 7/16" on any hole that didn't line up correctly.  No reason to remove more metal than is necessary.  The original holes in the AW-4 (that were used in the XJ setup) were actually a fair bit larger than what I ended up making....maybe 1/16" or there about.


They say that the proof is in the pudding....but in this case, it will have to be the studs on the t-case fitting cleanly through the newly drilled holes in the AW-4.  OH YEAH!  Gotta love the way they line up.  I should have bought a lottery ticket that day....I was on a role! 

More AW-4 Tranny Swap



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