Adapting the

Jeep 4.0L I6 Engine

to the

Chevrolet & GM Hydramatic Transmissions

Widely considered to be the best automatic transmissions in the world, General Motors HydraMatics make for outstanding upgrades into Jeep powertrains. This adapter assembly brings the Jeep / Mopar 4.0L engines together with Chevrolet style automatic transmissions, including the TH350, TH400, TH700R4, 4L60, and Early 4L60-E* transmissions.

Note that this kit is currently under redevelopment and not available for purchase at this time. 

Product & Features


The Adapter

This plate style adapter is precision laser cut and machined. Precision CMM mapped and machined, offset dowel locators and fastening points assure total concentricity for long transmission life. The adapter is plated in black zinc for corrosion resistance and appearance.


Kit contains zinc plated adapter, flexplate, flexplate reinforcement ring, flexplate spacers, dowel locators, crank spacer, crank position sensor, CPS mounting bracket, a shield plate with a convenient access port for your torque converter bolts, hardware, and instructions.

Applications & Compatibility


The Chevrolet style HydraMatic transmissions, including the:

  • TH350
  • TH400
  • TH700R4
  • 4L60
  • Early one piece case 4L60-E*
  • 4L80E*

*The electronically controlled early 4L60E and the 4L80E will require a transmission control unit, which - while effective - are somewhat expensive. The installer could consider the conventionally controlled 700R4. In the case of the 4L80E in a Jeep seeing truly hard service, it may be well worth the extra expense.

The later style 4L60-E (removable bellhousing, hex rear bolt pattern) are not candidates for this conversion.

The TH350 is the only candidate for 1972-1983 CJ5 Jeeps due to their length, and these Jeeps must not have excessive lifts.

Torque Converter 

The majority of these transmissions torque converters have the standard size three-bolt pattern that is 10.7" in diameter. Some factory or aftermarket heavy-duty TH400 and 4L80E torque converters, often seen in RV and heavier truck applications, may use a larger bolt pattern diameter or 6 bolts which is not compatible with the flexplate included with this kit. You may exchange this converter towards one with the standard diameter bolt pattern. The transmission portion of the TH350 and TH400 are identical and interchangeable. 4L80E converters are available in the smaller pattern as well. The converter can be rated at any duty or stall you wish. 


All Mopar style 4.0L engines from 1991-2004 are compatible with this conversion. For AMC 258, 304, 360 & 401 adaptations, see this page.

Renix era 4.0L engines (1987-1990) and SFI 4.0L engines (2005-2006) are not compatible with the Crankshaft Position Sensor (CPS) included in this kit. You may choose our standard 258 / 4.0L adapter kit and use a separate, harmonic balancer style Crankshaft Position Sensor relocation kit.

Related Products

Crank Position Sensor

The included Crank Position Sensor is an industrial grade unit built for great longevity. But, instead of mounting this CPS obscured inside the transmission bellhousing, it installs externally, making it field-replaceable. Extra sensors are inexpensive and compact enough to carry in any toolbox.


Transmission Cooling

Transmission Cooling is critical to the life of all automatic transmissions. Conventional in the radiator tank coolers are simply not adequate for long life on a Jeep’s transmission. Here are the products we recommend for best performance and ease of installation.



Additional related products for these applications will vary greatly based on the engine selected. We have engine mounts, cooling products, transfer case adapters -- the full gamut of products you would need for your conversion. The links below and navigation to the left will guide you to the correct pieces.

Transmission Controller 4L80E



Transmission Shifters for the TH350

Your TH350 will require a shifter assembly to work properly. If equipped with an automatic shifter on the column and you would like to keep that method of shifting, we recommend this kit:


We also offer two cable shifter kits that work well. This will be best determined by your personal preference depending on the Jeep it is going in, certain shifters work better. We have special brackets for the TJ to accept a special shifter version in the console. Other quality shifters made for the TH350 will also work well. We have found that the cable versions are usually easier to install and position correctly.


Installation Requirements

The adapter is easily and quickly installed onto both engine and transmission. The installer will need to pay attention to the flexplate-to-torque converter spacing and shim as appropriate (shims included).

Installation of the included CPS assembly will require that a 1/2" hole be drilled into the bellhousing of your HydraMatic transmission. This is a simple and rapid process and will not affect the integrity of the transmission case. A drill jig and instructions are included.

This conversion also requires the use of a 1980’s era, CJ 258 I6 starter in lieu of the 4.0L starter. You can exchange your starter towards a new or remanufactured CJ starter at your local parts house.

Transmission Location & Transmission Mounting 

When replacing the AX15 transmission with the TH350, driveshaft lengths can remain the same. The TH400 and 700R4 / Early 4L60E conversions are longer and will require length modifications to your driveshafts. Crossmember mounting for these transmissions is generally simple, and discussed in greater detail for these transmissions in our Transmission to Transfer Case Adapters section.

Engines & Engine Mounting

mmtj-g3If converting to a V8 in conjunction with this upgrade, aftermarket engine mounts are available to ease its installation. Because of the broad spectrum of engines and vehicle combinations used with this adapter, it would be difficult to list them all here. Whatever your application, Novak likely has the perfect solution. From a 225 Buick V6 in a CJ2A to an LS3 in your JK, we’ve got you covered. 

Novak's engine mounts, featuring excellent vibration dampening, superior strength, and impressive adjustability - adjustable even after the engine is installed. The design, strength, and affordability of our mounts are second to none.

Engine Placement Drivers Drop

Engine placement in these applications is an effort in compromise to find the best position overall as a package. Generally the engine will be about 1” or even more towards the right, (passengers’s side in the USA) away from the front differential in a Wrangler or similar application. This gives the best balance of weight (and more importantly clearance) for the driveshaft going to the front axle. Clearance is usually quite good in these applications; both the steering and front driveshaft push things towards the right. Fore and aft position will vary with the Jeep model and engine. Have a CJ5 and Gen I with a rear distributor? You’ll be better off a little forward for more rear driveshaft length and clearance for that HEI. If you are in a longer Jeep and using an LS engine with no distributor, you’ll have more fan clearance and better balance if you hold it to the rear. Usually for ground clearance tuck things up nicely for height to avoid damage to oil pans and other life giving parts in the Jeep. Common sense and taking a step back to look at things overall goes a long way.


Driveshaft length changes are often required. Most conversions to these transmissions will require that the rear driveshaft be modified to be shorter and front driveshaft longer.

Some installers, concerned about the expense of new or modified driveshafts, attempt to let the existing driveshafts dictate engine, transmission and transfer case location, often to the detriment of the project. Our recommendation is to prioritize the correct position of drivetrain components over saving a few dollars which is usually regretted in the long run with compromised positioning.

Driveshaft modifications and rebalancing can be affordable when performed by driveline, RV or tractor implement specialists. New driveshafts are an option, but not necessarily a requirement in regards to the actual successful conversion if your existing driveshafts are in good condition.

Jeeps that require extensive travel or specialty-built driveshafts have this option available through several fabricators across the nation. These are normally specified after placement of the new transmission and measured at vehicle ride height. As the rear driveline gets shorter, it is often advantageous to us a Double Cardan or “CV style” rear shaft with the correct geometry at the axle to minimize vibrations and possible binding. 


Use of factory axles is completely acceptable with this conversion. Axle upgrades are not necessary, but they may be chosen for reasons external to this transmission upgrade.

Also See