Adapting the

Dana Spicer Models 18 & 20 Transfer Cases


Divorced Mounting

Our divorced mount Dana 18 & Dana 20 conversion permits the use of a variety of different transmission applications and vehicle platforms.

Product & Features


The Adapter 

The Novak divorced mount adapter is 5.75" long, as measured from the transfer case face to the center of the universal joint. The adapter itself is cast and machined high-grade aluminum alloy, featuring thick flanges and a heavy cross-section. The adapter shaft is machined from triple-alloy gear steel mounted in twin bearings to sustain moment loading from the forces of the transfer case helical, involute input gear. 


Kit includes adapter housing, shaft, bearings, gaskets, seal, 1310 input yoke, hardware, and instructions. The kit will come pre-assembled and ready to install to your transfer case.

Applications & Compatibility

divorced_dana_18_20_side_viewTransmission Versions 

Any transmission you deem appropriate for your project is compatible. We provide a 1310 input yoke to which you will connect a jackshaft from your transmission output. 


Transfer Case Versions

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
  • 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.

Related Products

Transmission Rear Mount

This transfer case adapter's design is based on Novak's Universal Series adapters that feature a modular mounting and support system. Included with the adapter kit is a steel base that is a highly configurable mounting foot, and is ready to accept our industry standard urethane isolator mount, available for purchase. This is our preferred rear mount unit. Our kits are designed for it, and its usage is essential to protect powertrain components from the flex and movement typical of any automobile, but especially Jeeps.

Whether you are assembling onto a stock crossmember/skidplate or if you are setting up a high-clearance skid plate, you will find it to be a clean and simple process.


Dana 18 & 20 6 Spline Input Gears


D20 Transfer Case Shifters

The stock transfer case shifter may be used, possibly requiring minor modifications. On the Dana 20 it is often advantageous to use a new twin stick style shifter, especially if you are able to remove the interlock pins during the transfer case rebuild process. Multiple models are available depending on your original transmission mated to the D20. It is also possible to retrofit a longer length shifter by using our replacement tubing and TX20-COM4 sold below. You will likely need to re-bend the shifter levers for correct positioning but this gives a sound starting point. Going this route allows the shifter to be positioned further forward in relation to the transfer case which allows a location closer to stock as the transfer case moves back with the longer length TH350.


This is the tubing necessary to fabricate a custom length shifter, sold by the inch.

All would require the


D18 & D20 Rebuild and Gasket Options


Gasket and seals kit


Dana 20 Billet Pan and PTO Cover

These rigid and precisely machined billet bottom pans are the answer to a few Dana transfer case dilemmas. The thick, smooth-finished flange replaces the thin, warped factory pans and they virtually assure a drip-free seal. The PTO cover does the same for the back, plus they add a little “bling” to your case.


Dana 18 & 20 3.15:1 Upgrade Gearset


Installation Requirements

Assembly of this kit is very straightforward. However, overall fabrication, mounting and layout considerations may make a divorced mount conversion a more advanced project.

divorced_dana_18_20_top_viewClocking Information & Driveshaft Clearance 

The Novak adapter maintains factory clocking of your transfer case.

Transfer Case Shifter 

This transmission conversion will allow for the retention of the factory Dana 18 twin-stick shifters, Dana 18 single-stick shifter, and many of the Dana 20 shifters. This aspect will depend largely on your installation.

Yoke & Driveshaft Clearance

Use of the factory size driveshaft and yoke is recommended, but there is room for larger units if desired. Our adapter design has maximized clearance between the transmission and yoke. No transmission modifications are required for clearance on this wise.


Driveshaft length changes will be required, as this geartrain combination is longer than most factory Jeep combinations. However, since the transfer case can be divorced mounted, the driveshaft angle can be shared and mitigated between the jackshaft and the rear driveshaft.


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 of our customers, fearful at the perceived expense of new or modified driveshafts, attempt to let the existing driveshafts dictate engine, transmission and transfer case location, usually to the detriment of the project. Our recommendation is to always value the correct position of drivetrain components over saving a few dollars which is usually regretted in the long run with compromised positioning. Sometimes the application allows use of the existing shafts without modification. While that is perfectly acceptable, it should not be the first priority. 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. Novak can also accommodate your needs on this if provided with dimensions for the shafts at a reasonable rate.


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.

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