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AW-4 Transmission Swap


The above photo shows what can sometimes be the toughest parts to find for your project.  These were cut from a totaled '98 XJ that still had its vehicle wiring harness intact.  From personal experience, it is apparent that most salvage/junk yards will not cut connectors out of a harness unless the harness was physically damaged in the wreck.  A complete vehicle harness commands a good price on the used market.  A harness with missing tranny connectors doesn't.  As you can see, I was able to get the matching halves of both the gray and black plugs (as previously mentioned) as well as the 26 pin plug that is needed for the TCU (upper right corner of the photo).  The salvage yard owner was a pretty nice guy and reluctantly sold me the gray, black, and TCU plugs for $20.  He had one of this yard rats cut the connectors from the harness (I got to supervise!).  Since the young kid had quite a time getting the TCU connector out of the vehicle (the driver's side door was smashed in from the accident and so getting under the driver's side dash was a major pain), I gave the kid a tip and tossed the owner an extra $10.  At that point in time, I was on the start of my second day walking the junk yards looking for a '98-'01 donor XJ....and so when I finally found one that had the plugs still in it, I was pretty happy.  The owner, the yard rat, and myself parted company all better off than when we first met.  FYI, I had already checked at the Jeep dealership's parts counter and those plugs are NOT available without buying the entire harness (you can imagine what that might cost).

In all honesty, one could implement a work around for the gray and black plugs if they were not available.  It would cost you $10 to purchase a pair of 9 pin molex connectors like those shown in the photo.  You would then cut the black and gray plugs from the transmission's wiring harness and attach the new 9 pin connectors.  The matching halves of these two connectors would then be spliced into your TJ's wiring harness in the exact same manner that the gray and black plugs in the above photo will be attached to my TJ.  The only drawback to this is that IF you ever swapped in another AW-4 to replace the one you have, you would have to spend 30 minutes to convert its gray and black plugs over to the 9 pin connectors that you were using.  By the way, those 9 pin connectors can be had from your local Radio Shack store.  (I'll explain their intended use later in the project.)

It is mandatory that you obtain the 26 pin TCU connector.  Doing a work around for that is next to impossible.  There is nothing at the local Radio Shack that could be substituted for the real thing (unlike the gray and black plugs).  I would not even consider soldering the individual harness wires to the TCU's connector pins.  No way!  You need the tranny computer connector, period, end of discussion. 

While there will be more about the TCU's wiring harness later in the project, I'll provide a little bit of info here so you can get an idea of what is involved.  If you have acquired the AW-4 as I did, with its black and gray plugs intact, and you have the matching halves of those two plugs along with the TCU connector, what you will be doing is making a wiring harness that attaches those plugs together (and to your TJ).  To do this, one first needs a spool of 18 gauge stranded copper wire.   Skip the trip to Radio Shack for the wire as they usually sell it in 25' rolls and the pricing is too high for the amount you will need.  Try a good automotive parts store or a well stocked electrical supply store.  I recently came across a company called Del City and they have a great selection of automotive related electrical components and their prices are competitive. 

You will also need a good soldering iron or gun, rosin core solder (do NOT use acid core solder!), and several feet of heat shrink tubing.  The simple description of the task is that you will solder pre-cut lengths of wire onto the pigtails of the connectors.  Each soldered connection is then covered with a piece of heat shrink tubing.  The other end of the wire is connected to one of the other plugs.  When you are done, you'll have a harness with a 26 pin TCU plug on one end with a gray and black plug on the other end.  There will also be a handful of wires that will be connected to your TJ's harness (more on that later).  It is not technically difficult since the wiring diagrams are provided for you in this write-up.  If you can not solder neatly, solicit the help from a friend that does neat work.  It doesn't have to be NASA space shuttle quality, but it does have to be done correctly so that you won't have electrical problems on the trail.



OK, back to the transmission.  Here is a photo of the passenger side where the two cooling lines connect to the tranny.  The XJ had aluminum hard line cooling lines that were routed up to the radiator.  I've decided not to use the TJ's radiator for tranny cooling for a couple of reasons.  First, I do not wish to run my tranny fluid through a 210F radiator in hopes of keeping it cool.  In my opinion, that is warmer than the fluid needs to be.  I hope to keep it in the 150F~190F range most of the time.  Secondly, with the winch parked up front, the TJ has a fairly maxed out cooling system when cruising down the freeway in mid-August in central Arizona.  Adding tranny heat to the existing cooling load will simply add to a potential problem.

Update:  OK...so it has been a few years since I've installed the AW4 in my TJ.  Based on the info/experience I had at the time, I opted to not use the TJ's radiator to cool the tranny fluid.  Knowing what I know now and the experience I've had with my AW-4 swap, I would route the tranny fluid through the vehicle's radiator and then to the same 12V aux cooler that I currently use.  I omit the use of the stacked plate cooler in front of the radiator that is shown in this write-up.  The reasons for this....the ATF doesn't warm up well in the winter months (and our winters here in Phoenix would be MUCH warmer than most any other place in the country).  I would also I'll get better fluid coolring for highway and city traffic in the summer.  It is not an issue on the trails, but more so as one drives around time.  I believe the 4 LO on the trail makes the torque converter's job fairly easy.

Since I am not using the tranny's hard cooling line, the quick disconnect fittings in the above photo need to be replaced with something that will meet my needs.


I cut the aluminum line with a tubing cutter and took the fitting with me for a quick trip to the local speed/performance shop.  Note that this place is NOT a 4x4 store....it is stacked with gear heads that do car things, not Jeep things.  But they have a big wall full of hose ends and adapters....and that is what I needed for this part of the project.  The o-ring was seated at the end of the threads against the body of the fitting.  (hold on to it, you may need it)


A pair of Russell adapters were purchased at the local performance shop.  The Russell adapter part # is 648070.  It is a -6 to 14mm x 1.5 fitting and was just under $11 each.   These thread directly into the AW-4 fluid ports where the quick disconnect fittings were removed.  The counter guy at the speed shop tossed in the tan -6 o-rings (not included with the new fitting) since I spent $200 in the store before I walked out.  He mentioned that these adapters are commonly used for power steering boxes.  With these adapters installed, I have a -6 AN connection that allows me to connect the -6 (3/8") fluid cooling hose to the transmission.  If the o-rings on the factory quick disconnect fittings appear to be in good shape, they can be used on the AN adapter.


More AW-4 Tranny Swap



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