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AW-4 Transmission Swap


So, Bob thought of another method that did work.  I stood at the front of the engine and using my Herculine strength, I turned the pulley on the front of the crank shaft until one of the four mounting holes in the flex plate rolled into position (as you can see in the above photo).  By the way, the above photo was taken at the front of the vehicle, looking towards the rear, along the driver's side of the oil pan.  With the mounting hole now in position, Bob was able to sneak a couple of fingers into the dust shield opening and rotate the torque converter.  It was easy to see the converter's mounting tab line up in the flex plate mounting hole.  When it was lined up, Bob slipped a torque converter mounting bolt through the flex plate and into the mounting tab of the torque converter.  BINGO!  Once the first bolt was in place, it was easy to get the remaining three inserted.

After that, I only had to continue to rotate that crank shaft pulley while Bob put the bolts in place.  How come the little guy always gets the tough jobs? 

When all of the bolts were in place, we made one more go around (that pulley was getting harder to turn) and tightened the bolts to 23 foot pounds.

The tranny was now installed and it was time to slip the transfer case onto the end of the AW-4. 

HOUSTON, WE HAVE  A PROBLEM! 

ScottK made the comment in his write-up, in regards to the NP-231's input shaft length, that a t-case setup with a Tera 4:1 already had the short input shaft and as such, would not have to worry about changing it.  I am here to tell you that is wrong.  While the Tera 4:1 input shaft is in fact 3/8" shorter than a regular t-case being pulled off of an AX-15, it will still bottom out in the AW-4 and NOT allow the tranny and t-case mounting flanges a flush fit.  It is right at 1/4" too long.

I was faced with a couple of possible solutions, although none had been explored, to the best of my knowledge, by someone with a Tera 4:1 t-case under these circumstances.

ScottK solved his "too long input shaft" problem by simply buying a short shaft and installing it in his stock t-case.

Since the input shaft is part of the planetary gear set, and I had a 4:1 planetary gear set, I am not at all certain I could even find someone with a short input shaft.  At the very least, I would have to open up my t-case and see just what I was dealing with in regards to the planetary.  I called Tera a couple of weeks prior to the tranny swap to get their input on what I may or may not experience.  They were kind of "you mean you are going to put a Cherokee tranny in a TJ?" and so no help was obtained.

Bob and I scrounged an old 231 from Troy's discard pile and verified that the input shaft did in fact have to come out of the planetary gear set in order to be worked on.  Since I was under a self imposed time schedule for this swap, I didn't want to spend yet more time playing around with the t-case inner workings and even then, I would have to find a machine shop that could do the work once I had the input gear removed from the case.  I checked with Troy and he was not setup to do lathe work on hardened steel.  (yeah, we checked the junker input shaft and it was hardened)

Troy suggested I take a cut off wheel and slice the end of the shaft off.  Sure, easy to say....but how well would it work when tried?  OK....it was either that or drop a couple of grand on a new Atlas II t-case (Troy even had a short shaft sitting there for it.  That just isn't fair!)

 

I grabbed a ratchet strap from the back of the TJ and strapped the t-case down to a metal work table (kind of reminded me of a metal operating table.....just not as clean). 

A length of masking tape was used to mask a line along the input shaft, 3/8" from the end of the shaft.  (Since the input shaft bottomed out with a 1/4" gap remaining between the tranny and t-case, I decided to add the extra 1/8" just to make sure there was no pressure on the AW-4 seal.)  I used a blue marker to lay a light blue edge on the tape....the idea being that if the blue started to disappear, I was getting off of the designated line.  Finally, I took a paper shop towel, folded it several times, and taped it in place....making a large "dust cover" for the seal that was about an inch away from where I was going to be working.

A cutoff wheel was put on a right angle grinder.  Bob and I donned hearing protection and safety glasses.  Bob did the honors of steadily rotating the output shaft (with the t-case shifted into 2HI) while I ran the cutoff wheel.  If things got screwed up, it was pretty much my fault since turning the shaft wasn't going to make or break this part of the procedure.

 

I ran the cutoff wheel for about 30~45 seconds at a time while Bob rotated the shaft for me.  Steady pressure, cutoff wheel perpendicular to the shaft, don't get it too hot as you don't want to heat stress the shaft material or melt the seal that was less than an inch away....NO PROBLEM!  And if I screwed this up, what was I going to do?  Easiest part of the project thus far!

But in all seriousness, it worked GREAT!  It took us about 20 minutes to cut the shaft.  30~45 seconds of cutting and then a short cool down period (maybe 3 minutes).  The heat was drawn out of the shaft pretty quickly (faster than what I anticipated).  The other end of the input shaft has that BIG gear on it sitting in an ATF bath. 

The final dimension for the t-case input shaft was 13/16", as measured in the above photo.  You can see the piece that was cut off laying on the operating table.  As you can also see in the photo, I put a slight bevel on the edge of the shaft, similar to what was previously there.  The same right angle grinder with a flapper disk in it worked very well for this.  I held the grinder in one position while Bob rotated the shaft.  I wanted the edge dressed off to help avoid nicking the AW-4 seal when the shaft was slipped into the tranny

I cleaned up the shaft, removing the tape, shop towel, and metal filings (not really too many of those as they were flying all over the place in a shower of sparks).  A thin film of grease was applied to the inner and outer surfaces of the shaft.  Time to see the fruits of our labor.

Bob and I walked the t-case over to the tranny and slipped it into position.  It fit like a glove....and a perfectly sized glove at that! 

I think it is safe to say that more time was spent trying to figure out what to do with the input shaft than it did to actually do it.  Thanks to Greg and Troy for suggesting the cutoff wheel idea.  Troy was confident that Bob and I could make it work.  And once we made the first cut, I felt pretty good about it myself. 

The benefits to doing it this way....I didn't have to spend $125 like ScottK.....there was NO delay time waiting for a machine shop to do the work....and if it didn't work, I would have thought of something to blame on Bob!  (sounds like a win-win situation for me) 
 

More AW-4 Tranny Swap

 

 

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