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, compatibility with excellent engines, and ease of installation.
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". 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 is completely supported by this shaft and, while helical cut, is subject to side loading. The two bearing design is much better equipped to handle these loads.
The 103 Kit includes adapter housing, adapter shaft, bearings, seals, correct locator for your transfer case model bore, hardware, and instructions. These parts will come assembled to the extent possible.
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.
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.
This conversion is compatible with all Jeeps. 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.
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.
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.
Our adapter shaft is splined for six spline input gears.
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.
The diameter of the transfer case center input locating bore will be either 3-5/32" or 4".
If necessary, we offer a good, used version of the 4wd output shaft for your TH350.
Novak’s RM103 mount is optional, but highly recommended. As shown in the photo it is a strong and easy way to attach the rear mount. Hard mounting is not acceptable. If you don’t have other plans then this really is an essential part.
Because the transmission and transfer case shifters are often in a different location than factory in these Jeeps, this new transmission tunnel cover gives the installer a clean slate. There are no screw holes nor transmission & transfer case shifter holes, allowing the installer to drill and cut them as necessary. An easy way to get a perfect fit is to use the old cover as a template, making cuts as necessary, then overlay on the new aluminum piece for perfect holes.
The finish is natural brushed aluminum, which looks pretty terrific, but it can easily be primed and painted to suit, if desired.
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
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
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.
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.
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.
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.
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.
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.
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.
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.