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Adapting the

Chevrolet & GM Engine Bellhousings

to the

Jeep T90 Transmission

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.

Adapter Kit Options

Jeep Adapter kit to GM Bellhousings

Kit G9N, adapting GM bellhousings to the Jeep T90A & T90C transmissions, short version

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.

T90 to GM Adapter Kit

Kit C1, adapting GM bellhousings to the T90A transmission

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.

Jeep Adapter kit to GM Bellhousings

Kit C3, adapting GM bellhousings to the T90J transmission

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.

Applications & Compatibility

Compatible Engines

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

T90 to Chevy Bellhousing
The Novak #G9N kit with Chevy bellhousing

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.

T90 Versions

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 adds ~$180 to the expense of the conversion and 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.

Related Products


GM crank to Ford pilot bushing

Bushing, pilot, GM Gen. I-III (1955-2000) cranks to Jeep T90 & T86 transmissions, #PB-3901136

This pilot bushing is for classic Chevy, Buick and other GM cranks to many Ford input shafts. This includes early GM Gen III cranks that have the extended depth crank flange. Click here for more details on these pilot bushings.

Jeep T14 to GM pilot bushing

Bushing, pilot, GM Gen. III (2001- ) cranks to Jeep T90 & T86 transmissions, #PB-6071136

This pilot bushing fits in GM Gen III+ Vortec / LS cranks and matches the pilot tip of the T90, T86 & T98 as found in these Jeeps.

Ring, sizing, precision, 4-11/16” GM bearing retainers to 5-1/8" bore bellhousings, #BR-4

Press this ring onto the retainer of the Novak adapter if you have the 5-1/8" truck bellhousing as found on so many GM engines from 1968-1991. If you are unsure of the bore diameter of your Chevy bellhousing, you can buy this ring and return it if unused.

Release arm for 1945-1971 Jeeps with GM engine

Kit, arm, clutch release, GM engines to pre-1972 Jeeps, with pivot ball stud kit, #K-RAV6-N

This is the release arm with the proper geometry for 1945-1971 Jeeps that are retaining their through-floor pedals and bellcrank system. It is the most frequent choice for T90 conversions. This arm is the improved Novak designed release arm that avoids the problems with aftermarket arms. Spring retention pivot stud included.

Jeep to GM Clutch Release Arm

Arm, clutch release, GM engine to post-1971 Jeeps, #RAGM

As discussed above, this is the release arm needed to release a GM clutch disc when retaining the factory 1972-1986 bellcrank linkage system in CJ and some other models of Jeeps. This is not a common arm for this conversion as most T90's are in 1945-1971 Jeeps.

Adjustable clutch release throwout bearing

Bearing, clutch release, throwout, Novak adjustable, GM version, #TB1

This release bearing assembly uses a telescoping and locking design which spans the range of shortest to longest GM throwout beareings that were ever available. It is helpful if the installer wants a one-and-done solution that avoids trips to the parts store, and sometimes for bearing heights that just aren't made anymore by GM or the aftermarket.

Hydraulic clutch retrofit kit for GM bellhousings, #HCR

Novak's popular HCR series clutch release slave kits will bolt onto your existing GM (Chevy or Buick) bellhousing and provide you with the foundation for a strong, smooth, adjustable, servicable and durable clutch release system. See the details and options here.

Hydraulic release master kit for Jeeps

Assembly, clutch line and flex hose, stainless and poly wrapped, 7/16-24 inverted flare, DOT fittings, 46-1/4 in overall length, #HCR8

This durable hose will join your master cylinder to the Novak hydraulic slave kit.

Hydraulic release master kit for Jeeps

Cylinder, hydraulic clutch release, master, Jeep YJ, 1987-1990

This YJ master cylinder is great for upgrades from CJ bellcrank mechanical linkages to hydraulic, used in conjunction with Novak's #HCR slave cylinder assembly, adjacent. The CJ usally has markings on the firewall for its installation, and our instructions will show you how to set up the pivot points, pedals, etc.

Adjustable clutch arm pivot

Pivot, ball stud, clutch release arm, adjustable, GM bellhousings, #3855G

This handy clutch release pivot stud is what we reach for when setting up a clutch system. Unlike factory GM pivots, it can adjust for better clutch arm geometry and clearance with the bellhousing window.

GM LS Vortec Bellhousing

Bellhousing kit, GM LS / Vortec engines, #GM621-LS-K

Kit, bellhousing, GM Gen III+ engines to Muncie / Saginaw transmissions, 4-1/16” bore, compatible with 168 tooth flywheel & 12” clutch. Includes the pivot stud, release fork boot and flywheel cover.

GM Chevy Bellhousing

Bellhousing kit, classic Chevy Small & Big Block engines, #3899621-K

Kit, bellhousing, Chevy 90 degree engines to GM transmissions, 4-11/16 bore, 12” clutch, 168 tooth flywheel, enhanced casting. Includes the pivot stud, release fork boot and flywheel cover.

Extended depth flywheel for GM engines

Flywheel, GM Gen III/IV V8 engines, 168 tooth, offset version, billet, SFI, 35 lb, for standardized 12” clutches, #LS400-35X

This flywheel standardizes LS engines so they can use standard off-the-shelf clutch kits like earlier Chevrolet engines. Their extended height makes up for the shorter cranks in most LS / Vortec / Gen III+ engines. Bolts and clutch kit available, adjacent.

Bolts for GM engine flywheel to crank

Bolts, 11mm x 1.5mm, LS engine crank, extended length, 4.8, 5.3, 5.7, 6.0L, LS1, LS6, #330-2802

These bolts will fasten your flywheel to your GM Gen III+ crank. They are high-strength alloy and feature the unique GM thread pitch.

Clutch disc for T90A & T90C

Disc, clutch, 15/16”-10 spline hub, 10.5” OD, T90 transmission to GM bellhousings, #CD1516110

If using our #G9N kit and retaining your T90A or T90C with the 15/16" x 10 spline input shaft, use this clutch disc in your 10-1/2" GM pressure plate.

Clutch disc for T90A & T90C

Disc, clutch, 15/16”-10 spline hub, 11.0” OD, T90 transmission to GM bellhousings, #CD1516110

If using our #G9N kit and retaining your T90A or T90C with the 15/16" x 10 spline input shaft, use this clutch disc in your 11" GM pressure plate.

GM clutch kit

Kit, clutch, GM & Chev. V8, 11”, 10 spline x 1-1/8”, includes pressure plate, disc, alignment tool, #04-049

This kit is compatible with classic factory Small Block 168 tooth flywheels for many Chevy engines. It features a pressure plate with good holding power but civilized release pressure. Compatible with #C1 and #C3 kits above.

GM clutch kit

Kit, clutch, GM & Chev. V8, 12”, 10 spline x 1-1/8”, includes pressure plate, disc, alignment tool, #04-064

This kit is compatible with the Novak LS flywheel (adjacent) and classic factory Small & Big Block 168 tooth flywheels for most Chevy engines. It features a pressure plate with great holding power but civilized release pressure. Compatible with #C1 and #C3 kits above.

GM clutch kit

Kit, clutch, GM & Chevy 10-1/2”, 10 spline x 1-1/8” spline, incl pressure plate, disc, alignment tool, #04-021

This kit is compatible with classic factory Small Block 153 tooth flywheels for many Chevy engines. It features a pressure plate with good holding power but civilized release pressure. Compatible with #C1 and #C3 kits above.

T90 Rebuild Parts

Kit T90MR-J, master rebuild, T90 transmission, Jeep, 1945-1971, includes Novak extra-hardened counter shaft, #T90MRJ

While disassembly is not necessary for this conversion, many installers opt to do a T90 rebuild. They're a terrific gearbox for these Jeeps and this engine combination. Read more about our unique T90 rebuild kits here.


Engines & Engine Mounting

GM Engine Mounts for JeepsNovak 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:

  • 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
  • When mocking up your engine installation location, pay special attention to radiator and fan clearance.
  • Firewall modifications are not expected.

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.

Driveshafts

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.

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.

Also See

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