AdaptersAdapting the
Turbo Hydramatic 350 Transmission
to the
Jeep Models 207, 231, 242, 249 & 241OR Transfer Cases
Our TH350 transmission to the Jeep New Process (or New Venture) transfer cases 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, compatiability with excellent engines and ease of installation.
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The adapter kit is designed for compatibility with the Jeep NP207, NP231, NP242, NP249 & NP241OR "RockTrac" transfer cases.
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 of a high-grade aluminum alloy, featuring thick flanges and a heavy cross-section.
TH350 Versions
Any version and year of the TH350 can be adapted to the NP transfer cases, from Chevy, to Buick / Olds / Pontiac and Unicase versions of the TH350, as determined by your choice of engine.
Transmission Output Shaft
Every #131 kit comes with a new output shaft for the TH350, whether for 2wd or 4wd transmissions. 2wd versions work equally well as 4wd versions. The Novak output shaft is of an alloy steel, precision splined and hardened for a superior interchange. This shaft connects the TH350 output directly into the existing 21 or 23 spline NP / NVG input shaft for the strongest combination.
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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. |
Installation requires disassembly of the transmission main assembly, and we recommend the services of a transmission professional. The basic installation is 3-4 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.
Transfer Case Input Gears
The included Turbo 350 output shaft splines in directly into the OEM Jeep input gears, and transfer case disassembly is not typically required.
Transfer case input gear styles vary. Order your adapter assembly accordingly.
NP 231
The NP231 may have 21 or 23 splines. For more information about these variations of the 231, jump here.
NP 242, 249 & 241OR
The NP242 may have 21 splines for the 1987-1990 versions. When connected to the 4.0L HO engine (1991- ) the 242 will have 23 splines.
The NP249 and NP241OR always have 23 spline input gears.
NP207
The NP207 may have 21 or 23 splines. Many versions feature extra-long input gears whose stick-out lengths (as measured from the front edge of the input gear to the transfer case front mounting face) is longer than 2.2". These will require shortening with a cut-off saw and/or lathe and finished with edge breaking chamfers.
231 Rebuild Components
It is not requisite that you rebuild your Jeep transfer case to successfully complete the conversion, but it may be a good time to do so if your transfer case leaks or has many miles of service. We've made our NP 231 rebuild components available for this purpose.
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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 (below). This is our preferred rear mount unit. Our #131 kits are designed for it, and its usage is essential to protect powertrain components from the flex and jar typical of any automobile, but especially Jeeps.
Whether you are assembling onto a stock cross member / skidpan 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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| The Novak #SK2X shifter assembly as attached to our #131 adapter kit with the 350 automatic. |
Transfer Case Shifter
This transmission conversion will allow for the retention of the factory shifters, or allow you to upgrade to the Novak #SK2X shifter assembly for a simpler conversion and a clean shifting, direct linkage system.
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.).
Driveshafts
Driveshaft length changes are often required, as this geartrain combination is typically longer than factory Jeep combinations. However, some GM engine installations will allow for the transfer case to remain in its OEM location.
| Installers should note a possible benefit of the TH350 - usually done in conjuction with a Chevy Small Block engine conversion - of possibly not having to change or modify driveshafts in some YJ & TJ Jeeps. The TH350/Novak adapter combo is about 3" longer than the stock AX5, BA10/5, AX15, and NV3550 transmissions. However, most Chevrolet engines install 3 or more inches ahead in the engine bay, offsetting that difference. |
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.
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| Our RadLock radiators offer an available integrated transmission cooler, to greatly add to the life of your HydraMatic transmission. |
Since driveshaft modifications may be indicated for the conversion, it may be a good time to convert the transfer case to a heavy duty mainshaft and ultra-short tailhousing assembly. The #231XS Slip-Yoke Eliminator is the ideal solution to capture 7" of driveshaft length, significantly reducing u-joint strain and vibration.
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, 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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| Novak's MM Series 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. |
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.
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 Jeep transfer case both considered.
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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| We’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 alloy steel, instead of 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. The Novak shaft in our #131 kit is produced faithfully to factory specifications, and using even better steel. Our 4-axis CNC cut of the spiral gear and other features are no small tasks, and likewise, no small benefit to our customers dedicated to putting their Jeeps together right. |
| 21 vs. 23 splines We're often asked about whether the 21 spline style connection is strong enough, vis a vis the 23 spline version. In most situtations, 21 splines will be adequate. This is due to the fact that we don't use friction welding on our shafts, and that much of the punishing torque multiplication takes place within the transfer case low range, which occurs after the input portion of the transfer case. However, we have seen limited instances where 21 spline shafts have failed where 23 would not have. If you are certain that you must have maximum strength, then you may purchase from us a 23 spline input gear for your NP231 in conjunction with the 23 spline version of our kit. However, this may not be money best spent in some situations. |