These adapter kits adapt classic standard shift GM bellhousings to the T90 three-speed, as was the popular transmission found in 1946-1971 Jeeps.
All of these adapters install onto the T90 without full disassembly of the transmission. Cutting the transmission input shaft is not required as the adapter spaces the transmission properly for the GM crank and clutch assembly.
The #G9N is 3/4" thick and does not require a new input shaft or cluster gear. It utilizes the factory input gear and works with the 2.79:1 first-gear T90A or the 3.34:1 first-gear T90C. This version will not work with the T90J, long input shaft transmissions. It is machined from 6061-T6 billet aluminum. Included are the adapter, GM bellhousing locator / throwout sleeve, seal and hardware. Note that we do not recommend the G9N for military versions of the T90 transmission - see Applications & Compatability below.
The G9N may require to moving the T90 & Dana 18 transfer case forward ~2" in the Jeep to avoid engine interference with the firewall. This will require a floor/tunnel cover modification for shifter clearance but allows a longer rear driveshaft.
The #C1 kit for the T90A transmissions is 2-5/8" thick. This adapter is machined of a high-grade heat treated aluminum alloy featuring a precision machined bearing retainer. Included are the adapter, replacement input shaft of the correct length, GM bellhousing locator / throwout sleeve, seal and hardware. The C1 does require the installation of a new input shaft.
The #C3 kit for the T90J transmissions is 2-5/8" thick. This adapter is machined of a high-grade heat treated aluminum alloy featuring a precision machined bearing retainer. Included are the adapter, GM bellhousing locator / throwout sleeve, seal, and hardware.
Our included retainer is configured for the standard 4-11/16" bore bellhousing. If you have a truck style, 5-1/8" bore bellhousing, add our #BR4 sizing ring to your order, below. The #C3 does not require the installation of a new input shaft.
Nearly all GM Generation I-III engines are compatible with this conversion, including Chevrolet Small Blocks, Gen III+ V8's, Chevrolet V6's and Chevrolet I6 engines. Also, Buick, Olds, Pontiac, and other GM engines are compatible with this adapter assembly if you have a standard shift classic GM bellhousing and flywheel for your engine. Even some of the front wheel drive and unique engines could be made to work with this adapter using certain factory or aftermarket bellhousings sharing this common bellhousing / transmission bolt pattern.
GM bellhousings typically feature either a 4-11/16" rear face bore or a 5-1/8" rear face bore, the latter typically only from Chevy / GM trucks from 1968-1991. Our adapter will work with both. If you are uncertain of your bellhousing bore, choose the 5-1/8" press-on spacer ring that can be used or omitted to cover either situation. The ring is easily returnable for credit if not used in the installer's application. See Related Products, below.
If you are not sure of your T90 version, see this guide.
The T90A is found in 1946 to 1962 CJ2A, CJ3A, CJ3B, CJ5, CJ6, M38, M38A1, and also four-cylinder Utility Series Wagons & Trucks.
The T90J is found in 1952 to 1965 four-wheel-drive Utility Wagons & Trucks and Wagoneer & Gladiator Trucks when replacing the I6-226 and 230 "Tornado" engines.
The T90C is found in 1963-1971 Jeeps. Installers should note that a #C1 conversion to this version of the T90 would require a new cluster gear. This raises the 1st and 2nd gear ratios from 3.44 to 2.98. This may or may not be in the swapper’s best interest. However, contact us if you do want to go this route. A GM transmission like the SM420 or SM465 may be a better option in this case.
The military version of the T90 transmission is not recommended for use with the shorter G9N adapter because of its protruding shift rail bosses on the top cover, which will interfere into the GM bellhousing unless clearancing is done. We recommend the #C1 or #C3 kits in this scenario.
The clutch actuation will require adapting and fabricating either a mechanical linkage from the existing system or retrofit to a hydraulic system.
Novak engine mounts are available to ease the installation of your GM V6 or V8 engine. Novak has engines mounts for most Chevy, Buick and GM Gen III+ V8's.
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.
Engine placement in these Jeeps should consider the following points:
Since Jeeps featuring the T90 transmission are both low-hood & high-hood models, you will need to choose your motor accordingly. Clearance for classic Small Block and high Vortec (truck style) intakes and accessories is not a problem for the high-hood Jeeps. Low-hood Jeeps will require low profile car intake & and accessory engines.
Driveshaft length changes are required for the #G9N kit, lengthening the rear and shortening the front by about 2". #C1 and #C3 conversions typically keep the T90 in the factory location, precluding the need to driveshaft length changes.
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.
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.