1991 AX15 4x4 swapped with 1998 Cherokee AW4

[Luke.m]

I decided to swap from my internal slave AX15 on my 1991 to an AW4.  I got tired of wheeling the manual in the very steep terrain here in the mountains and just wanted the convivence of an automatic and I was tired of whenever the Master Cylinder went bad it leaked brake fluid on the fuse panel.  I went with the AW4 since it is bolt in, I can keep my transfer case that I had already swapped the shifter out of it for a 97+(which makes the neutral a true neutral, prior to 97 Neutral locked the front and rear drive shafts together while disconnecting from the transmission) and had a new chain in it.  I split a parts 1998 cherokee with a friend who wanted the axles so everything else was mine. After paying him for gas money and his time to go get it, I was into it for $250.  All AW4 transmissions are hydraulic and electronicly controlled for shifting.  The TCU(transmission control unit) is independant from the engine.  The absolute simplest way, but more work in my opinion is to find a donor cherokee that is similar in year(1990 or early for renix or 1991-1995 for OBD1) and swap everythign including the wiring harness.  I chose to chop out the harness I needed from the 1998 and took every possible part that was connected with the automatic.  This included shifters, trans tunnel plates, the 4x4 shifter and trans tunnel brace.  For the harness there will be the connector going to the TCU and 2 connectors going to the transmission.  Get wiring diagrams for the appropriate year comanche as well as your donor vehicle. I took my choppped wiring harness apart and followed wires to determine which wires need 12 volts always hot and 12 volts hot in ignition. A good wiring diagram is pretty easy to read, there should be 1 always hot wire and 2 hot in ignition. Additionally, the TCU requires 2 wires to be spliced into the throttle position sensor and 1 wire spliced with the backup light switch from the manual transmission. The manual transmission has 2 wires for the reverse light switch, one is a 12 volt hot(which I just capped off) and the other is the wire that goes to the reverse lights(this gets spliced with the appropriate wire from the TCU).  The wires from the TCU to the transmission will be with the plugs that I saved from the harness I cut out, its pretty obvious when you are following connectors from the TCU to the transmission before you cut the harness. 

 

There is a pilot bearing that needs removal before the AW4 can be installed and the flexplate that needs to be used will be the one appropriate for the comanche's PCM(renix with renix ect).  Pre 1991 comanches will also need the throttle body and throttle cable bracket from the donor for the kickdown cable, 1991+ will have provisions in place for installation.  The AW4 will install easily, just like any XJ and there are plenty of videos out there showing the flexplate installation and ect, before you try to install, make sure the torque converter is fully seated.  Fully seated it should make you wonder if it is touching somethign on the transmission, if you can kinda sorta get a figure between the torque converter and the transmission then its not seated far enough. The transmission mounts are different between the AW4 and the AX15 but the cross member works  with either.   After splicing in the TCU to the TPS and attaching power, the rest is just plug and play.  The CPS is the same between an AX15 and an Aw4 but I did notice that the pickup area on a flywheel is .5" larger than the pickup on flexplate, this may explain why it seems Auto's have more CPS problems than manuals, at first mine was a crank no start until I took a grinder to my CPS to it would sit closer to the flexplate, then it started but would miss above 2,000 RPM. I ground some more to set the gap at 1/8"(I had cut a hole in my trans tunnel while the transmissionw as out in anticipation of CPS problems).  This corrected my CPS problems.   On test drive, it shifted automatically through all 4 gears very smoothly including downshifts with throttle. Make sure your CPS wiring is secure otherwise your exhaust melt it.   

 

This process can be used to put any AW4 into any 4.0 jeep as long as there is a TPS signal to be used.  If the vehicle it is going into is newer than 1998, there may be a transmission code thrown, but there are writeups for putting Aw4 into TJ's regarding that issue.  

 

The AW4 is 1.5" longer than the AX15.  I managed to reuse my drive shafts for now but I should get htem altered. I have 6-7" of lift and an after market front drive shaft that does work in the front since it was already longer than stock. My rear drive shaft is still slip yoke and is stock length. It is barely short enough to be used, but I am concerned it may ruin the transfer case output seal, but its at least driveable.   If used in a wranger, a slipyoke elliminator will regain the 1.5" in the rear. 

 

I am also adding a rad design rail shifter into my comanche. To wire that in, there is a 6 pole switch that is wired with the 2 wires that go to the solenoid on the center poles. On one end of the switch is the TCU and the other end of the switch is the rail shifter. This lets selection of manual shifting or TCU controlled shifting. There is an additional switch that is wired similarly for the torque converter to select automatic lockup, no lockup or manual lockup.

 

I do not have a NSS at all in this vehicle since it is still a manual PCM with a manual wiring harness.

Credit to Ken Stein for his knowledge on the AW4 transmission.

 

https://www.naxja.org/forum/showthread.php?t=1053970#:~:text=The AW4 transmission was used,converter containing a lockup clutch.

 

 

Additonal credit to Rory @ rad designs for telling me about how he put an AW4 into a 1980 wagoneer.

 

https://www.radesignsproducts.com/

 

[jamespwsullivan]

Great narrative. Some pics might be nice but anyone who has spent a few years wrenching probably should be able to follow this.