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In the Beginning

In the summer of 2006 Larry acquired a 1993 Wrangler (there is a description of how we four-linked his YJ in another part of the build ups section of the web site). After the previous modifications the YJ is both a great highway and off-road vehicle. It will take moderate to difficult obstacles with finesse. However, about a year later the manual five speed transmission started acting up with what seemed to be a synchro problem. About 50% of the time it just would not properly shift into first or second gear.

We had been urging Larry, an old die-hard manual transmission man, to put an automatic transmission in the YJ. And it just so happened that when his tranny started acting up we had a 1997 Cherokee AW4 four speed automatic transmission just sitting in the lot. Although Larry is all for manual transmissions, he is also cheap. So when it came to the cost of rebuilding or replacing the manual versus installing a virtually free auto… Well, free won out. We’ll let Larry tell the rest of the story.

Larry's Story

These guys have me all wrong. It’s not that I think that manual transmissions are the only way to go. It’s more that I’m of the opinion that if it ain’t broke, don’t fix it. This jeep had a perfectly functional transmission that allowed me to do anything I felt capable of doing on the trail. That is until recently when the tranny finally gave up the ghost. So, as was mentioned previously, there was this automatic transmission available. The two main advantages of using this transmission were that it was a direct bolt on to my engine and transfer case and, unlike the regular Wrangler automatic transmission, it had overdrive.

It did present one problem, though. The transmission was electronically controlled via a computer and my YJ did not have the capability of controlling it. So I decided to do a little research to find out if this swap was even feasible. I discovered that indeed it was. As it turned out, even though the tranny is computer controlled it does not use the vehicle computer, more properly known as the power control unit (PCU), but is instead controlled by a separate computer called the transmission control unit (TCU). How’s that for an original name?

A little more research on the internet revealed that other people had successfully integrated the Cherokee TCU and transmission into TJ Wranglers. To do this, however, in addition to the transmission I needed a TCU and the appropriate mating connectors for the TCU and transmission. As luck would have it, there was a full Cherokee wiring harness and a TCU lying right beside the transmission. The TJ swap articles also provided wiring information to integrate the TCU and transmission into the Wrangler electrical system. I was good to go, or so I thought.

The transmission, TCU and XJ Wiring Harness

XJ Transmission

 

Here are links to a couple of excellent descriptions of XJ to TJ tranny swaps

For those of you who may be contemplating an AW4 to YJ swap here is a PDF of the interconnection diagram I developed and pin-outs for the appropriate connectors.

On the following pages I describe how we installed the XJ tranny into the YJ.

 

 

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