AdaptersAdapting the
GM 4L60-E (later version) Transmission
to the
Jeep Models 207, 231, 242, 249 & 241OR Transfer Cases
Our 4L60-E (including the 4L65 & 4L70) to the Jeep New Process (or New Venture) transfer cases conversion makes for the most refined assembly both on-road and off-road, and has become one of our most popular transmission to transfer case combinations.
Choose a seal spacer sleeve if your transfer case has a short input gear (discussed below). If you're not sure of the length of your input gear, you may order the spacer and then return it for full credit if not used in your conversion. |
The adapter kit is designed for compatibility with the Jeep NP207, NP231, NP242, NP249 & NP241OR "RockTrac" transfer cases.
The Adapter
The Novak 4L60-E to Jeep NP / NVG transfer cases adapter is very compact at only 3.0" long for a combined transmission and adapter length of 24.5" (equivalent to a 17.5" manual transmission). The adapter itself is cast and machined of a high-grade aluminum alloy, featuring thick flanges, a heavy cross-section and strength-adding gussets.
4L60-E Versions
Any versions (2wd or 4wd) and year of the HydraMatic transmission can be adapted to these transfer cases. There are no inherent advantages to the 2wd vs. 4wd transmission.
These kits are for the hexagonal, six-bolt tailhousing 4L60-E, typically made starting in 1996. Some 1997 and earlier versions have a four-bolt pattern tailhousing and non-removable bellhousing. See our Kit #171 if this describes your transmission.
Transmission Output Shaft Replacement
Every #4L61 kit comes with a new output shaft for the 4L60-E, 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 double-hardened for a superior interchange. This shaft connects the 4L60-E output directly to the existing 21 or 23 spline NP / NVG input shaft for the strongest combination available.
Installation requires disassembly of the transmission main assembly, and we recommend the services of a transmission professional, though good work is within reach of the home mechanic. 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 if necessary.
Transfer Case Input Gears
The included 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 by length and spline count. If your transfer case has a short style input gear, add our #SS231 seal spacer, above.
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NP 231
NP231 input gears come in varying spline counts and lengths. Whichever you have, we've got you covered.
The NP231 may have 21 or 23 splines and a long or short style input gear - NP 242
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 - 249
The NP249 always has 23 splines, but may have a long or short style input gear - 241OR
The RockTrac will always have a 23 spline, short style input gear - 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
Vehicle Speed Sensor
The Novak adapter assembly integrates the Vehicle Speed Sensor (VSS) necessary for the operation of the 4L60-E's computer. This greatly simplifies the installation process and eliminates the need for a transfer case range switch circuit and logic, making all GM 2wd and 4wd engines, transmissions and their PCM's great candidates for the installer.
The Jeep speedometer cable or VSS can then be connected to the Jeep speedometer or gauge panel as per factory.
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Transmission Rear Mount
This transfer case adapter's design is ready to accept our industry standard urethane isolator mount, available for purchase. This is our preferred rear mount unit. Our kit is 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.
Transfer Case Clocking
Our adapter is clocked optimally for slightly better ground clearance than factory locations, which is actually quite good.
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.
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| Many of our customers upgrade their NP / NVG shifter while doing the conversion. Our #SK2X makes the conversion easier than it's ever been. |
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 sometimes required, as this geartrain combination is typically shorter than most factory Jeep combinations. Some potential conversion engine installations sit further ahead than OEM engines in the Jeep's bay and will allow for better driveshaft angles, especially when done with this very short combination.
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| The Lokar direct linkage transmission shifter offers a smart method of shift operation, especially for installers replacing a Jeep manual transmission with the automatic where use of the factory console and boot will contribute to a clean installation and a very factory look. Image courtesy of Lokar - TH350 shown. 4L60-E shifter similar. |
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. |
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 4L60E installation is typically done in conjunction with an Generation III GM engine conversion into the Jeep. These engines include the Chevrolet Small Block V6 & V8, from 1996-2006. Though Gen. III installs are much more prevalent, Gen II and Gen I motors installations are possible but will require the use of a separate transmission computer controller which may add significantly to the expense of the total installation.
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 4L60E 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.
| 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. |