AdaptersAdapting the
Turbo Hydramatic 350 Transmission
to the
Jeep & IH Dana Models 18 & 20 Transfer Cases
Our TH350 to Dana Models 18 & 20 conversion makes for a very strong, and capable assembly both on-road and off-road. It is one of the most persistently popular transmission conversions into Jeeps, providing a very compact geartrain, compatiability with excellent engines and ease of installation.
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About the Transmission
The Novak TH350 to Jeep Dana 18 & 20 transfer case adapter is very compact at only 2.9" long for a combined transmission and adapter length of 24.6", permitting installation 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.
TH350 Versions
Any version and year of the TH350 can be adapted to the Dana 18 & 20, from Chevy, to Buick / Olds / Pontiac and Unicase versions of the TH350, as determined by your choice of engine.
4wd versions of the Turbo 350 are all ready to bolt up to our adapter kit and transmission disassembly is unnecessary as the required style of OEM output shaft is already installed. This 4wd style output shaft protrudes 3/4" from the rear face of the transmission main case.
2wd versions work equally well, but you will need to add our #8641088 4wd style output shaft (box, below). This requires disassembly of the transmission, and we recommend the service of a transmission professional. This basic shaft installation is typically a 2-3 hour bench job and may include simple gasket and seal replacements. Some choose this as the time for a more thorough master rebuild and update of the HydraMatic.
Once installed, the GM TH350 4wd output shaft is compatible with and splines directly into the included adapter shaft. This new adapter shaft is machined from triple-alloy gear steel and provides superior strength as it is carried by twin bearings, unlike the other single bearing versions on the market.
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.
Transfer Case Input Gear
Our transmission mainshaft is splined for either six-spline input gears, or ten-spline input gears.
Six-spline gears (shown, right) are predominately most common, as found with the Jeep T84, T90, T86, T89, T98, T18, T15 & T150. - The rare ten-spline version is only availalble 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 type overdrives are compatible with this conversion. Spline count information is the same.
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.
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| The 4wd version of the TH350 will have a 3/4" output shaft stickout length. If your transmission is otherwise, see below: |
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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 essentially all of Dana 20 shifters, including the Twin-Stix Shifter Kit.
Transmission Shifter
A broad variety of transmission shifters are compatible with this conversion, ranging from console shifters (i.e.; Art Carr, B&M, etc.), to direct-mount stick shifters (i.e.; Gennie, Lokar, etc.).
Yoke to Pan Clearance
Use of the factory size 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.
Novak's optional #RM103 stainless steel mount base and urethane isolator assembly, as show attached to the adapter housing. This mount offers a strong and easy to configure crossmember mount for essentially all Jeeps. |
Transmission Rear Mount
You may configure your rear mount using the base of the TH350 case in conjunction with the transfer case side mount. Or, you can install the Novak #RM103 foot and isolator assembly.
This mount will sit onto your stock cross member / skidpan, into which you will drill two attachment holes. You will find it to be a clean and simple process.
Any installation should use a urethane rear isolator. Its usage is essential to protect powertrain components from the flex and jar typical of any automobile, but especially Jeeps.
Engine Compatibilities
The TH350 is easily compatible with most Chevrolet, Buick, Olds engines. The TH350 can be adapted to the AMC engines as well. For further details on engine compatibilities, read our Guide to the Turbo Hydramatic 350.
Engines & Engine Mounting
A Turbo 350 installation is typically done in conjunction with an engine conversion into the Jeep. These engines include the Chevrolet Small Block V6 & V8, from Generations I, II, & III, 1955-2006 as well as the Buick V6.
In any scenario, it is critical that the engine be installed (as the Jeep engines usually are) with an offset of 1" to 1-1/2" to the driver's side. Other engine mounts on the market - especially the bolt-in versions - do not take this into account and make other placement decisions for the installer that do not take the full powertrain into account.
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| Novak's MM Series engine mounts, featuring excellent vibration dampening, superior strength and impressive adjustability - adjustable even after the engine is installed. The design and strength and affordability of our mounts are second to none. |
Novak offers what we have found to be the most intelligent engine mounting system for Jeeps available, allowing the installer to make an easy and satisfying decision as to powertrain placement with the TH350 and the Dana case both considered.
Driveshafts
Driveshaft length changes are often required. However, some GM engine installations will allow for the transfer case to remain in its OEM location.
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, sometimes to the detriment of the project. Driveshaft modifications are usually inexpensive when performed by driveline, RV or tractor implement specialists. New driveshafts are an option but seldom a requirement in regards to the actual successful conversion. Jeeps that require extensive travel or specialty-built driveshafts have this option available through several fabricators across the nation.
Transmission Cooling
For every ten degrees cooler you can keep the transmission, you can add 25,000 miles to its service life. Therefore, use of a transmission oil cooler is advisable for this automatic transmission.
Use of a transmission temperature gauge is also a good idea. These are widely available and generally inexpensive.
We will suggest the use of our RadLock high-performance conversion radiators for 1972- CJ Jeeps, which can include an integrated transmission fluid cooler. You may also use a standalone / supplemental transmission cooler depending on your driving style and climate conditions.
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| As the TH350 is a popular option with GM conversions, consider our RadLock radiators for the best cooling available ('72-present Jeep Universals). |
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.