Our TH350 to Dana 300 conversion makes for a very strong, and capable assembly both on-road and off-road. It is one of the more popular automatic transmission conversions into Jeeps, providing a very compact geartrain and compatibility with a variety of engines.
The Novak TH350 to Jeep Model 300 transfer case adapter is very compact at only 3.1" long for a combined transmission and adapter length of 24.8". The adapter itself is machined from billet 6061 T6 aluminum, featuring thick flanges, a heavy cross-section and superior strength.
Billet adapter housing, transfer case input or output shaft (per kit selected), transfer case input shaft seal, transfer case to adapter gasket, transmission to adapter sealing ring, fastening hardware, steel mounting base and instructions.
Advanced computer modeling methods were integral to the design of our #135 adapter assembly. We were able to push the bounds of product and process well beyond the status quo.
All versions 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.
The 4wd version of the TH350 will have a ~3/4" output shaft stickout length.
4wd versions of the TH350 are ready to bolt up to our 135 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 is correct for this kit version. Partial disassembly of the transfer case is necessary to install a new matching 27 spline extended Dana 300 input shaft machined from triple-alloy gear steel. This provides a superior upgrade.
The input shaft installation is a 1-2 hour bench job and usually includes either a simple gasket and seal replacement or preferably a full rebuild of a tired D300. It is not necessary that you rebuild your Dana 300 to successfully complete the conversion. However, it is certainly worth consideration especially if your transfer case leaks or has many years of service. Our superior quality Dana 300 gaskets & seals kits and our all-inclusive master rebuild kits with stronger Novak manufactured center pin are highly recommended for this purpose.
The 135-S adapter is compatible with all versions of the TH350. If you have a 2wd TH350, a 4wd TH350 that is undergoing a rebuild anyway, are unsure what TH350 you have (or will have at the time of the conversion), or your D300 was just rebuilt (doesn’t leak) and you’d rather not open it back up the 135-S kit is your best choice. The new 23 spline 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 a 300 transfer case. 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.
The 27 and 23 spline shaft sizes are quite comparable in minor diameter (the diameter of the shaft at the root of the splines) and therefore, 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.
GM 27 spline and Jeep / Dodge 23 spline shafts have a history of great strength in factory applications and Jeep aftermarket set-ups.
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 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.
Jeep New Process 208, 219, 228 & 229 transfer cases use the same output shaft style adapters as the Dana 300. Used in 1980+ full-sized Jeep applications, they may be retained using these adapters and are fully compatible using the output shaft version. The simpler and more reliable NP208 can be a particularly worthwhile swap.
Our usual recommendation is to replace the older style transfer case (especially the troublesome 219, 228 and 229) with a newer, more modern version such as the part-time 231J with HD SYE kit installed and upgrades as appropriate. Also the 242 full-time case (particularly the AMG version as it is extremely strong) has the correct side drop and allows a mechanical speedometer output. Certain part-time Dodge 241 applications will also work. These more modern transfer cases allow the use of our cable shifter assemblies for a cleaner installation, have lower low range ratio, helical cut gearing, fluid pump, and are a newer more refined design. Read more about the differences here.
This conversion is compatible with all Jeeps. The TH350 is the only real automatic option practical for CJ5 and other short wheelbase Jeeps. You may consider our 133 Short Version and possibly shorter transfer case output shafts to further facilitate longer rear driveshafts in those applications.
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. This adapter opens up numerous possibilities as it can be used with all of the above mentioned native engines and any others that can be adapted via a front adapter such as our 437 series kits.
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.
The stock D300 shifter may be used, possibly requiring minor modifications. Often it is 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. For the Jeep Dana 300, we recommend two twin stick shifters. One features an adjustable length.
Another great option for the D300 is our Dana 300 Transfer Case Twin-Stick Shifter Kit which is a solid, high quality option but lacks the forward adjustability of the transfer case shifters. It has the option of billet knobs showing the engraved shift pattern.
All would require the
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.
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.
Two designs are available for the Dana 300: The shallower depth, low-profile version for Jeeps requiring greater ground clearance. This version increases fluid capacity over the factory pan by about 6 oz. The extended depth version that maximizes the fluid capacity for the most punishing service. This version increases fluid capacity over the factory pan by about 16 oz.
If you can accommodate the electronic speedometer or don’t need a speedometer option, this kit will give you the ultimate in strength and short length. Full details are here.
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.
If necessary, we offer a good, used version of the 4wd output shaft for your TH350.
If your input is worn or you would like a new input shaft with longer spline engagement to match your Novak output this part is an excellent choice.
Tools required will vary depending on which kit is selected. The automatic transmission takes more specialized tools and knowledge, gaskets, seals and snap ring pliers, etc. The D300 input will require bearings be pulled and pressed on the input, in addition to 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. 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 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. 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.
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, feature 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 ways.
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 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.
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.
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.