Adapting the Turbo Hydramatic 350 Transmission

to the

Jeep & IH Dana Models 18 & 20 Transfer Cases

Jeep Adapter kit to GM Bellhousings

Kit 103, adapting TH350 transmissions (4wd version) to Jeep & IH Dana Spicer Model 18 & 20 transfer cases

Our TH350 to Dana Models 18 & 20 conversion helps makes for a strong and capable powertrain, both on-road and off-road. It is one of the most persistently popular transmission conversions into Jeeps, providing a compact geartrain, compatibility with excellent engines, and ease of installation.

The Novak TH350 to Jeep Dana 18 & 20 transfer case adapter is compact at 2.9" long, for a combined transmission and adapter length of 24.6". This short length allows fitting in even short wheelbase Jeeps. The adapter itself is cast and machined of a high-grade aluminum alloy, featuring thick flanges, a heavy cross-section, and strength-adding gussets. The adapter shaft is machined from triple-alloy gear steel and provides superior strength as it is carried by two bearings unlike the other single bearing versions on the market. The Dana 18/20 input gear is rigidly supported by this configuration to handle gear side loads.

Kit Contents

The 103 Kit includes adapter housing, adapter shaft, bearings, seals, correct locator for your transfer case model bore, steel mount foot, hardware, and instructions. These parts will come assembled to the extent possible.

Our #103 adapter comes with a configurable mount foot. Attach a urethane rear mount like our #RMU, (see Related Products,below) for your crossmember. Do not hard mount this nor any powertrain component.

Applications & Compatibility

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.

Dana 18 & 20 Input Gasket

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.

TH350 Versions

TH350 Transmission Output Shaft Protrusion

The 4wd version of the TH350 will have a ~3/4" output shaft stickout length.

All versions and years of the TH350 can be adapted to the Dana 20. Chevrolet, Buick / Oldsmobile / Pontiac and Unicase versions all work equally well.

  • 4wd versions of the Turbo 350 are ready to bolt up to our adapter kit and transmission disassembly is unnecessary as the required style of OEM output shaft is installed. This 4wd style output shaft protrudes 3/4" from the rear face of the transmission main case as seen in the illustration.
  • 2wd versions work equally well, but you will need to add our U44678C 4wd style output shaft available, below. The basic installation is a 1.5-2 hour bench job and will include at least simple gasket and seal replacements. This is a good time for a more thorough master rebuild and update of the Hydra-Matic. Many consider one of our complete Novak remanufactured and upgraded transmission packages. The advantage of a professionally built transmission, tested, delivered and ready to bolt in is worth consideration.

your Front Output Yoke

With this Novak adapter, you will keep your existing 1310 front output yoke on your Dana transfer case. Because of the adapter design, a special downsized front yoke is not required.

Compatible Jeeps

This conversion is compatible with all Jeeps, though short wheelbase Jeeps shouldn't have extreme lifts. The TH350 is the only real automatic option practical for CJ5 and other short wheelbase Jeeps. These are strong transmissions, and Full Size Jeeps such as Wagoneers, J-Trucks, etc. are conversion candidates for them. There are numerous upgrades available for the TH350 should stock strength come into question.

Compatible Engines

Any engine that can be made to work with the TH350 will work with this adapter. All of the above mentioned native engines along with others that can be adapted via a front adapter such as our 437 series kits open up numerous possibilities. Note: AMC engines sit back about 3" more than GM swapped counterparts. As such, this may limit the amount of lift avaialble in a short wheelbase Jeep.

Related Products


Urethane Rear Mount for Crossmember
TH350 Transmission 4wd Output Shaft
Auto transmission cooler
1976-1986 Jeep floor tunnel cover
Dana 18 & 20 Input Gears
Billet aluminum Dana transfer case pan
Dana 18 & 20 Rebuild Kit
Dana 18 Billet PTO Cover
Dana 20 billet rear bearing cap

Installation Requirements

Driveshafts

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.

Axles

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.

Tools

Tools required will vary depending on which kit is selected. The automatic transmission takes more specialized tools and knowledge, gaskets, seals, snap ring pliers, etc. The adapter requires typical mechanic's hand tools.

Placement

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

Use of the factory diameter front driveshaft and yoke is recommended. Our adapter design has maximized clearance between the transmission pan and yoke, but it is necessary that you install your GM engine offset 1-1/4" to the driver's side. If you are installing against a factory AMC engine with our 437-AMC adapter kit, your factory engine should already have this proper offset.

Engines & Engine Mounting

If 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.

GM to Jeep Engine Mounts

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 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 left, (driver’s side in the USA) away from the front differential in a CJ application. This gives the best balance of weight and more importantly clearance for the driveshaft going to the front axle. your tight spots will be steering to exhaust on the left (hold that as tight as you can) and clearance for the front driveshaft on 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.

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