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Adapting the

Turbo Hydramatic 400 Transmission

to the

Jeep Models 300 & NP 208, 219, 228, 229 Transfer Cases

TH400 to Jeep transfer case adapter

Our TH400 to the Jeep Dana 300 and FSJ NP transfer cases conversion makes for an absolutely strong and capable assembly both on-road and off-road. It remains one of our most requested automatic transmission to transfer case combinations.

The adapter is compact at only 1.4" in length. This adapter assembly is the shortest Turbo 400 adapter in the industry, providing a combined transmission and adapter length of only 25.9" (equivalent to an 18.9" manual transmission / bellhousing combination). The adapter itself is precision machined of aluminum alloy. The adapter is drilled for multiple clocking options and features a modular mounting and support base, ready to accept our industry standard urethane isolator mount, available in Related Products, below.

There are a few kit options to choose from, depending on your configuration.

AMC vs GM TH400 Case Rotation

AMC Jeep style TH400 transmissions from 1976-1979 featured a tilted rear case casting for which we make an optional "A". Our unique adapter configuration corrects for this so it will sit level on the crossmember and not clock the transfer case unnecessarily low. Customers should choose this version only for AMC TH400s of the above era. 1966-1973 Jeep units featured "universal" cases that were level as conventional. These earlier cases are identified by their use of a factory 400 transmission to Buick or AMC engine block adapter.

Option I: Replacement TH400 Output Shaft, 23 Spline

Adapting TH400 transmissions to Jeep Dana 300

Kit 134-23, adapting TH400 transmissions to Jeep Dana 300 and FSJ NP transfer cases

Kit contents:

  • Adapter
  • Transmission output shaft, 23 splines
  • Seal
  • Seal spacer
  • Gaskets
  • Steel base foot mount
  • Fastening hardware
  • Instructions

The 134-23 kit is compatible with all TH400 versions and the following scenarios:

  • 2wd or 4wd
  • you believe it's time for a rebuild
  • Unsure of which version TH400 you have
  • you have a fresh transfer case that you'd rather not service
  • you have an FSJ New Process transfer case and don't want to change the 23 spline input gear

The provided 23 spline TH400 output shaft splines directly into the OEM style input shaft of a 23 spline transfer case. This requires disassembly of the transmission, and we recommend the services of a transmission professional.

The basic installation is a bench job, often including anything from gasket, seal and filter replacements to a full master rebuild and update.

Dana 300 to TH400 adapter

Option II: Replacement 32 Spline Dana 32 Input Shaft

Adapter kit for TH400 to Dana 300

Kit 134-32, adapting TH400 transmissions to Jeep Dana 300 transfer cases, Dana 300 32 spline input shaft version


134-32 Kit Contents

  • Adapter housing
  • Transfer case input shaft, 32 splines
  • Seal spacer
  • Seal
  • Adapter gasket
  • Seal ring
  • Fasteners
  • Steel foot for rear mount
  • Instructions

One 4wd version of the TH400 has the right, short NP208 & NP241 style, 32 spline output shaft (see graphic, below) for this kit version. Transmission disassembly is therefore not necessary for this scenario. Partial disassembly of the Dana 300 input shaft assembly is required and instuctions are included. If you would like a pre-built input assembly that is pressed together and ready, see our #300ISK kit in Related Products, below.

This kit is not compatible with the FSJ New Process transfer cases. See kits above and below.

TH400 NP208 style output shaft

It is not requisite that you do a full rebuild of your transfer case to successfully complete the conversion. However, it is certainly worth consideration if you are opening it up and it shows many years of service. For the gear, gaskets, chains and even full rebuild kits, see Related Products, below.

TH400 to Dana 300 transfer case assembled

Strength Comparison of 23 vs 32 Spline Versions

The 32 spline shafts are, as you would guess, stronger than 23 spline shafts. Whether this has practical meaning in a Jeep depends mostly on the power of the engine, the weight of the Jeep, the tire size and the style of driving and terrain.

We've corresponded with tens of thousands of Jeeping customers, and 23 spline breakage vanishingly rare. 32 spline breakage? We've not seen it yet. But if you are strength-maxxing and it's a real concern, you can go for the 32 spline connection.

Option III: Replacement 32 Spline New Process Input Gear

Adapting the TH400 to Jeep FSJ Transfer Cases

Kit 134-N32, adapting TH400 transmissions with 32 spline (short, 208 style) input shaft to the Jeep NP208 transfer case

If you have an NP208 version output shaft TH400 transmission, and want that full 32 spline strength, this kit includes a 32 spline input gear for your NP208, 219, 228 or 229 chain drive transfer case in your 1980's FSJ Jeep. As such, this kit is not compatible with the Dana 300 transfer case.

Disassembly of the transfer case is necessary to replace the factory 23 or 31 spline input gear with this unit. It may be a good time to do a rebuild and replace the chain while you are into it.

TH400 transfer case adapter

Kit contents:

  • Adapter
  • New Process transfer case input gear, 32 splines
  • Seal
  • Seal spacer
  • Gaskets
  • Steel base foot mount
  • Fastening hardware
  • Instructions

Applications & Compatibility

Compatible Transmissions

All versions and years of the TH400 can be adapted to these Jeep transfer cases. Chevrolet, Buick / Oldsmobile / Pontiac and Universal versions all work equally well. Many manufacturers sourced the TH400 from GM, even companies like Ferrari and Jaguar used them. As discussed above, 2wd or 4wd versions all work equally well with the correct adapter option.

TH400 transmission, adapted

Some customers request our complete Novak remanufactured and upgraded transmission packages. This master-built, professionally prepared transmission is constructed to your specifications, tested, delivered and ready to lift into your Jeep.

Compatible Engines

Any engine that can be made to work with the TH350 will work with this adapter. Natively compatible engines such as the Small Block Chevy, Chevy V6, Big Block Chevy, and even the 1997-2006 Vortec / LS / Gen III+ engines popular choices. However, be aware of engine crank spacing issues with Gen III+ engines when used against Gen I transmissions such as the TH400.

It's generally better to keep the TH400 with it's Gen I & II GM engines as per factory. Consider the 4L80E if you have the vehicle length to handle it, or the 4L60E built to Level II+ if you need rowdy strength and are going with Gen III+ engines. That said, the TH400 can be made to be compatible with them all.

AMC engines can be adapted via a front adapter such as our 437 series kits.

Compatible Jeeps

This conversion is compatible with most Jeeps. These are strong transmissions native to 3/4 ton truck applications. Full Size Jeeps such as Wagoneers, J-Trucks, etc. are also conversion candidates for them.

Jeep Dana 300 to TH400 Conversion

Related Products


Urethane Rear Mount for Crossmember

Urethane Rear Mount, #RMU

This rear mount bolts direct to your Novak adapter, and can be used with a variety of crossmember styles.

Auto transmission cooler

Cooler, auxillary, transmission, 29,200 BTU (HD recreational), 1 ½” NPT fitting, #OC-H7B

For every 10 degrees cooler you can keep your automatic, you add 25k miles to their life. This stacked plate style cooler is both rugged and efficient, and it's flanges make it easier to set up than other styles of cooler. See related cooler lines, adjacent.

Kit, automatic transmission cooler lines, braided stainless, 2 lines, 74” OAL ea, -6AN female thread fittings, #TR-FLX

Tough, flexible stainless lines with easy sealing AN fittings. We've installed these on so many Jeeps and they're an in-and-done type product and compatible with our #OC-H7B cooler, adjacent.

1976-1986 Jeep floor tunnel cover

1976-1995 Jeep CJ & YJ Floor Tunnel Cover

Start with a clean slate tunnel cover for your 1976-1995 Jeep CJ / YJ floor. Cut your shifter holes and install boots onto it as required. Material is aluminum. Can be painted. More info here.

Arm, pivot, shifter, Hydramatic 350, 400, 700, 4L60E & 4L80E Lokar, fully adjustable, #ACA-1802

This is the arm we reach for when setting up a shifter linkage to a GM automatic in a variety of Jeeps. The adjustable bellcrank gives the installer the freedom to set the proportion of throw to the same as the shifter in the Jeep, be it a column or floor shifter.

Dana 300 twin stick shifter

Shifter kits, Dana 300 twin stick

Shifter upgrades are frequently done with a transmission swap. See our options for shifters, boots and knobs for your Dana 300, here.

Twin Stick Boot

Boot, twin-stick, textured, with stainless steel bezel, #TSB

Choose this boot to use with the adjacent Dana 300 twin stick kit.

Dana 300 Rebuild Kit

Gaskets & Rebuild Kits for Dana 300 Transfer Cases

Replace the hard-working bearings and intermediate shaft of your Dana transfer case with one of these kits, all while sealing it up and getting your bearing endplay correct. See them and several other parts and kits here for your Dana 300.

Dana 300 Input Retainer Assembly

Kit, shaft, input, bearing w/retainer, preassembled with proper bearing preload, #D300-ISK

If you are uncomfortable setting up the input on your D300 or simply would like our stronger billet retainer and all new components pre-set for your transfer case, this is the perfect solution. This kit includes our billet D300 input retainer, new snap ring, bearing and seal all assembled to the included Dana 300 input shaft as part of the #453 kit.

Dana 300 rear bearing cap

Dana 300 front rear output bearing cap, #8131657-K

This innovative bearing cap uses o-ring sealing around its perimeter and bolt holes, then shims the bearing internally, instead of the leaky, exposed stack-up shims. This is one way Novak builds its own leak-free Dana 300's in-house.

Billet aluminum Dana transfer case pan

Dana Transfer Case Deep Billet Pan #D328D

A deep and rigid billet aluminum pan for your Dana 300 transfer case. More fluid capacity, better sealing and some anodized eye candy for your geartrain. Shallow version for better ground clearance also available here.

Dana 300 Super Short Tailhousing

Dana 300 Super Short Tailshaft Assembly, #300RX

Strengthen and shorten your Dana 300 in one shot with Novak's #300RX tailhousing assembly. The factory output shaft is the Dana 300's fuse, and the upgrade to 32 splines and an improved driveshaft angle will make a serious difference. See it here.

Dana 300 Exended Spline Input Shaft

Shaft, input, Dana 300, 23 spline extended depth splines, factory length, #8131687E

Some factory 300 input shafts have excessively worn splines. This extra hardened replacement is an upgrade in materials and design, featuring extended splines to maximize the connection to your 23 spline output shaft 700R4 kit above.

TurnKey TH400 Transmission Package

TH400 Transmission Package, Turn-Key

Sourced, remanufactured and built in-house to Levels I, II or III. We then dyno test them, and profesionally package and deliver it to your location, adapted and ready for installation. See and order one here.

Also available as part of our popular Turn-Key powertrain program.


Installation Requirements

Tools

TH400 in rebuild jig

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 snapring pliers. Installation after the output shaft or input gear isin place requires normal mechanics tools.

Powertrain Placement

Urethane transmission mount
Our #RMU urethane mount (Related Products, above) is the ticket for nearly every Jeep swap we've seen. Whatever you do, do not hard mount this nor any powertrain component. Flexibility is critical to prevent breaking your transmission case.

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.

Engines & Engine Mounting

Engine placement in these Jeeps should consider the following points:

  • Left-right offset location is similar to factory at ~1-1/4" to the driver's side
  • Avoid installing the engine too low (axle clearance and other issues)
  • Avoid installing the engine too high (transmission tunnel interference, etc.)
  • Set your engine to 4-7 degrees of tilt rearwards, like the factory engine & powertrain
  • It is usually best that Chevy and Gen III+ V8 engines install approximately 3" further forward, using the back of the engine block face as the datum
  • When mocking up your engine installation location, pay special attention to radiator and fan clearance.
  • Firewall modifications are not expected.

Since Jeeps featuring the T18 transmission are "high-hood", clearance for classic Small Block and high Vortec (truck style) intakes and accessories is not a problem.

GM Engine Mounts for JeepsNovak engine mounts are available to ease the installation of your engine.

Novak's engine mounts, feature vibration dampening, superior strength and useful adjustability - adjustable even after the engine is installed. The design, strength, and affordability of our mounts are second to none.

Driveshafts

Driveshaft length changes may be required. Chevy engines (with their rear distributors) can install around 3" further forward than AMC engines. It is also recommended that LS family engines be installed 3" further forward than the factory block (using the back face of the block as the datum point) for exhaust clearance, firewall access, etc.

Because of the engine placement and transfer case SYE kits are frequently installed with many of these conversions, you may end up with a longer rear driveshaft (very desirable for lifted Jeeps) and a shorter front driveshaft.

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.

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.

TH400 passenger side view, adapted

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.

TH400 transmission, overhead view

Also See

TH400 drivers side adapted view