Jeep Wrangler AX-15 to 700R4 transmission swap
Why would you change from a stick to an automatic? Short Cuts
by: Ron Hollatz - 5/2000

700R4 ready to go into the Money Pit. Photo by author.
Tranny Cooler
Mounting the transmission cooler. Photo by author.
Engine Adapter
Engine to transmission adapter and flexplate. Photo by author.
Transmission and transfer case reinstalled. Photo by author.
Lion's Back
Does the auto work as well as a stick? Photo by Laurie Hollatz

It has to be one of the biggest debates of the Jeeping world, stick or auto? Every time I see the subject come up in one of our forums or mailing lists I know everyone will have an opinion. There are both advantages and disadvantages of each type, but you better be prepared to defend the choice you make. The automatic fans are quick to point out they don't have to worry about stalling the motor or shifting during difficult maneuvers, while the stick camp points out their lower first gears and that they don't have to worry about their transmissions overheating.

My 1994 Wrangler came with the 4.0L motor and AX-15 5-speed manual transmission from the factory. The AX-15 came with a 3.83 first gear, which works well for most off-road adventures, and is considered a medium duty transmission. A few years ago I added an Atlas transfer case from Advance Adapters, a Dana 44 in the rear, and 4.56 gears with lockers in both axles. Most people would have been happy with this, but I recently decided to take my Wrangler to the next level.

Choices, choices, choices

Since I started planning this swap last year, I've been checking out other Jeeps and talking with their drivers about their setups. The most common swap seems to be putting in a heavy duty truck transmission with a really low first gear. The transmissions include the SM420, SM465, and the NV4500. Any of these transmissions would have been a good choice but I wanted something different. A few years back I suffered a major ankle injury which made it uncomfortable to work the clutch during a long day on the trail. I've also been trying to teach my wife to drive my Jeep, but she didn't like using the stick shift. This simplified the decision to put in an automatic transmission.

Now that I knew I wanted to put in an automatic, I had to decide which one. The easy route would have been to choose one of the automatics Jeep has used with their 6 cylinder motors in Wranglers or CJs. The problem was that none of them is a 4-speed or has a low first gear. I considered swapping a Cherokee AW4, but it is computer controlled, which would add to the complexity of the swap. I've noticed a trend towards the General Motors automatic transmissions both on the trail and in the extreme rock crawling events put on by ARCA. One of these automatic transmissions, the TH-700R4, is a 4 speed with a 3.06 first gear. By using this transmission, I would have the overdrive for highway use, a decent first gear, and a future swap to a small block motor would be easier.

There is a lot of information available about the 700R4 since it was used in so many different vehicles. I tried to sift through all of it to find out what would be the best donor vehicle. The 700R4 was introduced in 1982 and was used in both cars and trucks. The early versions had some durability issues, but most of those had been take care of by the 1987 model year. The non-computer controlled 700R4s out of V-8 vehicles up to the end of production in 1993 are the most desirable. The transmission came in both 2-wheel and 4-wheel drive versions. Like most GM transmissions the difference is the added tail shaft housing on the 2-wheel drive version.

A rebuilt 700R4 can run quite a bit of money so my goal was to find a core and have it rebuilt. I was lucky enough to have a friend of a friend who is a transmission tech and was willing to rebuild a transmission for a reasonable price. I was unable to locate a 4-wheel drive core, but a local salvage yard had a 1990 Caprice police cruiser equipped with a V-8 and a 700R4. The cruiser was in rough shape but it drove so there wasn't anything major broken in the transmission. I ordered a B&M 700R4 Super Transkit which included pretty much everything to overhaul the transmission and sent it off to the rebuilder.

There are a lot of different options when it comes to choosing a Torque Converter. When building a performance car many people choose a torque converter with a higher than stock stall speed to improve off the line performance. I wanted to avoid this so I chose a B&M Traveler converter with a slightly higher than stock stall speed. The Traveler can also be used as a lockup converter. I also added a TCI Universal Lockup Wiring Kit to control the torque converter lockup. I'm still experimenting with the lockup to see what is the best setup. One of the disadvantages of a lockup converter is it generates more heat so I added the largest transmission cooler B&M offers.

So how do you fit that thing in there?

Now that I had the transmission, I had to figure out how to get it in the Jeep. I turned to the experts at Advance Adapters who specialize in drive train swaps of all types. Since the 4.0L shares the same block as the 258 used in Jeep CJ's I was able to use their AMC engine to GM transmission adapter and flexplate. The kit also included a new 23 spline output shaft for the 700R4 to match the input on the transfer case. My Atlas transfer case had the NP-231 bolt pattern, so I had to use one of Advance's adapters on the rear of the transmission. If I wasn't suffering from "Incrementalism" I'd be doing this all at once and I would have bought an Atlas with the 700R4 bolt pattern.

When I was planning this swap, a lot of people told me the combination would be too long. Surprisingly, the 700R4 and engine adapter are the same length as a stock AX-15. The transfer case adapter is only 2" thick and the Atlas is 2 1/2" shorter than a stock NP-231 transfer case so my rear driveline is pretty close to the stock length. I am using a C.V. driveline in the rear, so vibration hasn't been an issue yet. I replaced the front driveline with an "Extreme Slip" drive shaft from South Bay Driveline. I also installed a custom skid plate from Advanced Frame Works to protect the transmission and transfer case. The transmission mounting is located 2" back from the original location, and I used one of Advance Adapters cross member supports to make sure everything stayed where it belonged.

For the shifting duties I chose a shifter from Lokar. While they are mostly known for street rod components, their shifters can be modified to work in a Jeep. The shifter mounts to the top of the transmission and is controlled by a linkage instead of a cable. This allows for a smoother shift and also looks really cool. Several lengths are available for a customized fit.

Another necessary modification during this swap was to move the crank position sensor. Jeep mounted this sensor in the bellhousing and gets its signal from the flywheel. Since I would be removing the flywheel the sensor had to be moved to another location. The only option for automatic transmission swaps is a kit from Hesco in Birmingham. AL. Their kit moves the sensor from the bellhousing to the damper on the front of the motor. The kit includes a new damper, sensor, and sensor bracket. This is the same kit which is used for the Mopar fuel injection conversion.

With all this preparation, you'd expect the install to be a piece of cake, but a few challenges came up along the way. Stay tuned next month as I go through the install and how it worked in Moab.

On to the install

Contacts: Related Links:
  • Advance Adapters
    Dept. ORN
    4320 Aerotech Center Way
    Paso Robles, Ca 93446-0247 USA
    Phone 800-775-4407
    Fax 805-238-4201
  • South Bay Driveline
    Dept. ORN
    573 W. Julian St.
    San Jose, Ca 95110 USA
    Phone 408-995-6000
    Fax 408-995-6513
  • B&M Racing
    Dept. ORN
    9142 Independence Avenue
    Chatsworth, CA 91311 USA
    Phone 818-882-6422
    Fax 818-882-6694
  • TCI Automotive
    Dept. ORN
    One TCI Drive
    Ashland, MS 38603 USA
    Phone 662-224-8972
    Fax 662-224-9308
  • Advanced Frame Works
    Dept. ORN
    223 Stratosphere Dr.
    Lewistown, MT 59457 USA
    Phone 406-538-4996
    Fax 406-538-4997
  • Hesco Inc.
    Dept. ORN
    1329 Fourth Avenue South.
    Birmingham,AL, 35233 USA
    Phone 205-251-1472
    Fax 205-251-8358

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