AW4 swap into YJ -
  • 1 Post By bgredjeep
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post #1 of 2 Old 12-11-2017, 10:08 AM Thread Starter
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Location: Savannah
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AW4 swap into YJ

So I currently have a YJ 4.2l with a BA 10/5 manual tranny. I want to swap to a 4 speed OD. I have looked at all of the options and it seems for the money, the AW4 would be my best bet. (I would ultimately want to go with a 700r4 Gm but the conversion is going to cost too much) I have done a bit of research but cannot seem to find solid answers to many of my questions. I am sure they may have been answered on here a million times. Unfortunately the search option on this forum isn't the best. So maybe you guys can help get me pointed in the right direction.

So the first questions I have are about actual fit and connection of the unit. I assume I have the answers correct here but just want to check. If I understand correctly the AW4 should bolt to my engine without an issue, as long as it is an AW4 and not a A340 out of a Toyota. Are all the bell housings the same bolt pattern? Is there a difference in a 4cyl and a 6cyl bolt pattern? Not even sure this unit came in the 4cyl. Then in the back I am certain that my NP231 should bolt up, but I do understand there are 2 possible output shaft spline counts (21 and 23). This all should be pretty simple.

My next concern is the electronics. Now my YJ has a carbureted 4.2l and basically no computer controlling it. I understand that the aw4 is an electronic unit, but can run with a stand alone TCU. Or I have seen some guys basically wire a series of switches to make it shift manually. Does anyone have any experience with this, or maybe point me to some decent websites that might help? I am not sure of the connections to my YJ.

Finally is there a certain year or model unit I should be looking for are they all pretty much the same? I can find any info open if they change through the years they were in service.

Please keep in mind that I have weighed all of my options and I am 99% sure this is the unit I want to swap to. I would not like this thread to turn into the "Well you should just use blank unit instead of the AW4". I am particular about the fact that I want a 4 speed OD, and although I would love to have a GM model because they are bullet proof. I am not looking to pay a ton of money for adapter kits. I have considered the 42rh but ruled it out because the AW4 has a much better reputation for being durable. I understand the AW4 can be prone to overheating issues which is easily solved with a large trans cooler. So unless you have some information that contradicts the above statements, I don't think I will be changing my mind on the AW4.

Thanks in advance for your help.

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post #2 of 2 Old 12-15-2017, 09:32 AM
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1987 YJ Wrangler 
Join Date: May 2005
Location: Augusta, GA
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I can help with this. I swapped from a t18 to an AW4 in my crawler recently.

First, the AW4 will bolt to your 4.2. I installed one from a 96 XJ into my 87 YJ. I used an XJ flex plate, torque converter, and starter. Everything bolted right in. I would recommend a 91+ model trans for the 23 spline output shaft. I'm not sure if your current 231 behind the BA10 is a 21 or 23 spline, but if you are going to the trouble of the swap, I recommend the 23 spline and swap to a 23spline case if needed.

Second, the trans does use a TCU from the factory. This ties into the original engine harness on a Cherokee. There are diagrams out there explaining what you need to wire in the TCU for automatic shifting, but on a carb'd motor, I'm not sure you will be able. I understand it uses a speed sensor, CPS, and TPS, none of which you will have on a carb'd engine. I do have a Howell EFI on mine, but I didn't attempt to make my AW4 shift automatically.

If you aren't concerned about manually switching the gears on the AW4, check out They offer several options for shifting an AW4. They have controllers available for as low as $110 to control the shifting solenoids for manual selection of 1-4. The cheaper options are used in conjunction with the factory XJ shifter (for P-R-N-D selection). You put the shifter in Drive, then use the secondary control lever to switch your gears 1-4. For my Jeep, I went with the Winters shifter they offer with the control switches integrated so I don't have to mess with multiple shifters. It was a bit more expensive, but much easier to mount, and a cleaner install than if I used their baja controller. I literally connected 2 wires to trans for the solenoids, and a power wire to the shifter. No other wiring was required.

With just a standard XJ shifter, I believe the manual valve in the trans will allow you to hit 1st, 3rd, and 4th gear with no electonics, but I wouldn't recommend driving that way.

Here's a thread with some general AW4 info. There are also a few threads in the YJ section about members who have done, or are doing a similar swap.
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