Adapting the Turbo Hydramatic 350 Transmission

to the

Jeep Models 207, 231, 242, 249, 241J & 241OR Transfer Cases

Our TH350 transmission to the Jeep New Process (or New Venture) transfer case conversion makes for a very strong and capable assembly both on-road and off-road. It is one of the most persistently popular transmission swaps into Jeeps, providing a very compact geartrain, compatibility with excellent engines, and ease of installation.

Product & Features

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***Please read 21 spline notes below before purchase***

The Adapter 

The Novak TH350 to Jeep New Process transfer cases adapter is very compact at only 1.1" long for a combined transmission and adapter length of 22.9" (equivalent to a 16.4" manual transmission). Especially important for short wheelbase YJ & TJ Wrangler Jeeps, the Novak kit provides an excellent and popular transmission conversion combination. The adapter itself is machined 6061T6 billet aluminum alloy, featuring thick flanges and a heavy cross-section.

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Advanced computer modeling methods were integral to the design of our #131 adapter assembly. We were able to push the bounds of product and process well beyond the status quo.

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.

Rear Mount Provision 

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 and is available for purchase below.

Contents 

Kit contains billet adapter housing, transmission output or transfer case input, seal, transfer case to adapter gasket, transmission to adapter sealing ring, fastening hardware, steel mounting base, and instructions.

Applications & Compatibility

TH350_Unicase_with_103_adapterTransmissions

The 131 adapter is compatible with all versions (2wd or 4wd) and years of the TH350 can be adapted to the Dana 300. Chevrolet, Buick/Oldsmobile/Pontiac and Unicase versions all work equally well with the correct adapter option.

Transmission Output Shaft Versions

The 131-23 and 131-21 adapter is compatible with all versions of the TH350. If you have a 2wd TH350, a 4wd TH350 that is undergoing a rebuild anyway, your transfer case was just rebuilt (doesn’t leak) and you’d rather not open it back up, or you are unsure what TH350 you have (or will have at the time of the conversion) these kits are your best choice. The new TH350 output shaft is machined from 300M alloy steel which provides a substantial strength upgrade. The new Novak shaft splines directly into the OEM style input shaft of NP/NNVG transfer cases. This requires disassembly of the transmission, and we recommend the services of a transmission professional.

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 superior, professionally built transmission, tested and ready to bolt in delivered to you is definitely worthy of consideration.

This is the only version that will work with a 241OR Rocktrac transfer case or other applications where the input gear is incompatible.

Strength of 21 spline versions and warranty exclusion

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The 21 is substantially weaker than the 23 spline version. 21 spline versions were only used in the 4 cylinder applications and some very early automatic 6 cylinder versions. WE DO NOT OFFER A WARRANTY ON ANY OF THE 21 SPLINE SHAFTS because of this weakness. Our recommendation is to change the input to a 23 spline version as sold below and don’t put a drivetrain “fuse” in a bad location. On lower powered V6 applications in a lightweight vehicle driven conservatively you may get away with it.

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

Transfer Case Input Gear Version

4wd versions of the TH350 are ready to bolt up to our 131-27E and 131-27L adapter kit. Disassembly of the transmission is unnecessary as the 27 spline 4wd style output shaft which protrudes 3/4" from the rear face of the TH350 transmission main case which is correct for this kit version. Disassembly of the transfer case is necessary to install a new matching 27 spline input gear. This is useful if you have a good TH350 with 4x4 shaft as shown already installed especially if your transfer case is a 21 spline version as the 27 spline input offers much greater strength than a 21 spline output shaft version of the kit. This version will not work with a 207 or 241OR transfer case. The early vs late transition is about 1993. If you are unsure of the year of your transfer case or are near the border years, we always recommend verifying this by the width of the front bearing. Early versions are 24mm wide and the late 16mm wide. It is also possible that over the life of the Jeep, a transfer case swap may have occurred. 

The input gear installation is a 2-3 hour bench job and usually includes an RTV seal replacement. It is not requisite that you rebuild your transfer case to successfully complete the conversion. However, it is certainly worth consideration especially if your transfer case leaks or has many years of service. A full rebuild of a tired transfer case includes new bearings, seals, chain and an SYE kit. More information about these options can be found here.

Strength comparison of 27 vs 23 spline versions

The 27 and 23 spline shaft sizes are quite comparable in strength. Diameters are very close and the finer 27 spline vs the coarser 23 spline has shown no significant strength variation. The 300M material used in production of the Novak shaft is of a superior strength both in PSI yield and torsional resistance (which is exactly the type of load these shafts see). Aside from that, fundamental design strengths are comparable. Factory GM 27 spline shafts have proven to be very robust over a long history of use.

Output Shaft Strength

broken_advance_adapters_shaftWe’ve seen a handful of shafts broken like this one, and heard our customers speak of more failures of output shafts made by other adapter companies. This is why we go through the trouble and expense of making our output shafts from a solid bar of exceptionally strong 300M alloy steel, instead of lower grade alloys or friction welding salvage GM shafts. A second, sometimes less obvious but pernicious problem is the issue of warpage during friction welding and heat treating - which cannot be corrected when the shaft journals are already ground and worn at or below factory specifications. Novak shafts receive a final hard turn of bearing journals after the heat treat process with special tooling and cooling process to ensure the ultimate finish. The Novak shaft is produced to factory specifications with stress risers removed using much stronger steel alloy. Our 4-axis CNC cut of the spiral gear, oil feed passages and other features are no small tasks. This attention to detail, maximized strength through design and material along with precise tolerances provide the ultimate parts for your project.

Jeeps

This conversion is compatible with most Jeeps. These are strong transmissions native to 1/2 ton truck applications. 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.

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.

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.

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Transmission Tunnel Cover

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.

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New Process Transfer Case Shifter Options 

Often the shifters are linked to your old transmission, body, or both. As things move or even just to have a better setup these shifter solutions prove invaluable and extremely popular.

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Transmission Shifters for the TH350

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:

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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.

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Transmission Cooling

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.

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23 Spline Input Gears

If you have a 21 spline input transfer case, our recommendation is to replace the input gear with a 23 spline version. The NP/NVG input gears are divided early and late about 1993-1994. However there are no guarantees that the transfer case is original or that the gear change was made as a clean break 93 down and 94 up. If in question, the input bearing width on these models is a good indicator. “E” Early uses a 24mm wide bearing and “L” late is 16mm wide. The photos show the differences in width of the bearing location and the stepped shoulder between the bearing and the gear. 23 spline input gears are available to replace the anemic 21 spline found in all too many applications. Please select the appropriate gear below.

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Installation Requirements

Tools

The automatic transmission takes more specialized tools, knowledge, gaskets, seals and snap ring pliers, etc. Transfer case input installation takes normal tools along with some larger snap ring pliers. Installation after the output shaft or input gear is in place requires normal mechanics tools. Both transmission and transfer case side are 3/8” fasteners.

Placement

As these usually are installed as part of an engine swap setting the powertrain to the proper pitch angle is recommended - usually tilted down ~5 (3-7 acceptable) degrees. Offset will be to the right (passengers’) side because of the driver drop transfer case and front differential (usually 1 to 1-1/2”). 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 and driver’s side drop transfer cases usually clear nicely in most all applications.

Engines & Engine Mounting

mmtj-g3If 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

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.

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 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.

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.

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