Adapting the

New Process & Dana 300 Flanged Transmissions

to the

Jeep & IH Models 18 & 20 Transfer Cases

Adapter kit for 4L80E to Jeep transfer cases

Kit 152, adapting New Process & Dana 300 flanged transmissions to the Dana 18 & 20 transfer cases

Adaptation of newer Jeep four- and five-speed transmissions into earlier Jeeps is now feasible. This kit is only intended for Jeeps that have the length necessary to accommodate these longer transmissions.

The adapter is machined from 6061 aluminum. The included adapter shaft is available as a 23 spline input and 6 or 10 spline output. The adapter is 2" long. While this is very compact for a twin-bearing adapter, the mating transmissions may prove long for some early Jeeps.

Kit Contents

  • Adapter housing
  • Adapter shaft, 6 or 10 spline
  • Bearings
  • Bearing adapter, 3-5/32" or 4"
  • Seals
  • Fasteners
  • Gasket
  • Seal ring

These parts will come assembled to the extent possible.

Applications & Compatibility

Compatible Transmissions

While it is mechanically possible to run the overdriven transmissions against a Dana 18 that features a Warn style overdrive, consider that you would have an overall overdrive ratio of .525 (.70 in the transmission and .75 at the transfer case overdrive). Transfer case output speed would be nearly double that of the engine speed. While this is a fascinating thing and excellent for mileage if the engine can sustain the low RPM cruise, the velocities that it could turn within your Dana 18 may be overwhelming. Keep in mind that the D18 and its overdrive were not designed for that type of RPM use. you would likely run into oiling and sheer strength issues at those sustained speeds.

The following transmissions are possibilities for such a conversion, and their combined lenghts:

  • AX15, 16-1/2" (+ 7-1/2" bellhousing*)
  • NV3550, 16-1/2" (+ 7-1/2" bellhousing*)
  • NSG370, 24" (integrated bellhousing*)
  • T176, 16-1/2" (+6-3/4" bellhousing*)
  • T5, 17-1/2" (+6-3/4" bellhousing*)
  • TF999, 24-3/4"
  • AW4, 27-3/8"

Most of these lengths will not be appropriate for early CJs (pre-1972) with short wheelbases, unless the engine is a V6 and has been installed in as far forward a manner as possible.

*AMC / Jeep bellhousings. May vary slightly when adapted to GM or other bellhousings.

Compatible Transfer Cases

All Jeep models of the Dana Spicer 18 and Dana Spicer 20 transfer cases are compatible with this adapter assembly. IH versions of these transfer cases are also compatible. The correct input bore and spline count must be observed. This adapter is not suitable for the Ford Bronco transfer case as it is of an entirely different design in attachment and drop.

Transfer Case Input Gear

dana_18_20_input_gearOur adapter shaft is splined for six spline input gears.

  • Six-spline gears (shown, right) are most common and usually found behind Jeep T84, T90, T86, T89, T98, T18, T15 & T150.
  • The ten-spline version was only available on the 1966 - 1974 transfer cases against the Jeep T14 transmission and must be replaced with a 6 compatible spline version.
  • Factory Jeep TH400 to Dana 20 combinations had a fifteen-spline input gear, which must be replaced by a compatible six spline version.
  • International Harvester Dana 20's that had the TF-727 automatic had a 23-spline input gear, which must be replaced by a compatible six spline version.

Consult our informative Dana gears interchange chart if necessary.

All Warn and Saturn type overdrives are compatible with this conversion as long as the spline count is correct. We do not have replacement gears for the overdrive version.


Transfer Case Bore Size

The diameter of the transfer case center input locating bore will be either 3-5/32" or 4".

  • Most Dana 18's have a 3-5/32" bore, including those found against the T84, T90, T89 or T98.
  • Some Dana 18's have a 4" bore, including those found against the T86 & T14 transmissions (Buick V6 engines), 1966-1971.
  • All Dana 20's have a 4" bore, regardless of the transmission they were joined to.

Transfer Case Clocking & Rotation Options

Our adapter is drilled for multiple clocking locations from near-factory (20 degrees down) to near-flat (3 degrees down). However, pan clearances and front axle width may inhibit the flatter options.

Compatible Jeeps

Again, most of these lengths will not be appropriate for an early CJ (pre-1972) with short wheelbases, unless the engine is a V6 and has been installed as far forward as possible.

However, CJ8 Scrambler Jeeps, other longer Jeeps (especially the full sized trucks and Wagoneers) are ideal candidates if punishing transmission duty is a prime consideration.

Compatible Engines

Any engine that can be made to work with the transmissions listed above will work with this adapter, whether they be natively compatible engines, or adapted to the transmission.

Related Products

AX15 & NV3550 Rear Mount
Dana 18 Billet PTO Cover
Dana 20 billet rear bearing cap
Dana 18 & 20 Rebuild Kit
1976-1986 Jeep floor tunnel cover
Billet aluminum Dana transfer case pan
Dana 18 & 20 Input Gears

Installation Requirements


The adapter requires typical mechanic's hand tools. Detailed instructions are included for installation of the adapter to transfer case.


Transmission placement is largely determined by factory engine location. It is not necessary in typical conversions to change the engine position unless an engine is being swapped in at the same time, as will often be the case with these kits. Setting the powertrain to the proper factory or conversion pitch angle - usually tilted down ~5 (3-7 acceptable) degrees - is recommended. Consult our engine conversion guides for more specific recommendations on placement if the engine is being replaced.

Clocking Information & Driveshaft / Yoke to Pan Clearance

Our adapter is drilled for multiple clocking locations check clearance carefully as you complete the installation.

Engines & Engine Mounting

GM Engine Mounts for JeepsNovak engine mounts are available to ease the installation of your GM V6 or V8 engine. Novak has engines mounts for most Chevy, Buick and GM Gen III+ V8's.

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

Engine placement in these Jeeps should consider the following points:

  • Left-right offset location is similar to factory at ~1-1/4" to the driver's side
  • Avoid installing the engine too low (axle clearance and other issues)
  • Avoid installing the engine too high (transmission tunnel interference, etc.)
  • Set your engine to 4-7 degrees of tilt rearwards, like the factory engine & powertrain
  • It is usually best that Chevy and Gen III+ V8 engines install approximately 3" further forward, using the back of the engine block face as the datum
  • When mocking up your engine installation location, pay special attention to radiator and fan clearance.
  • Firewall modifications are not expected.

Since Jeeps featuring the T18 transmission are "high-hood", clearance for classic Small Block and high Vortec (truck style) intakes and accessories is not a problem.

Novak Gen III+ engine mounts for 1976-1986 Jeep CJ models will remove any guesswork from the engine installation location as they are predetermined for the best location and engine clearance margins.


Driveshaft length changes may be required. Chevy engines (with their rear distributors) can install around 3" further forward than AMC engines. It is also recommended that LS family engines be installed 3" further forward than the factory block (using the back face of the block as the datum point) for exhaust clearance, firewall access, etc.

Because of the engine placement and transfer case SYE kits are frequently installed with many of these conversions, you may end up with a longer rear driveshaft (very desirable for lifted Jeeps) and a shorter front driveshaft.

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.

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