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Adapting the

Chevrolet & GM Standard Shift Bellhousings

to the

Jeep T90 Transmission

This adapter assembly makes for a strong and convenient adaptation of classic standard shift GM bellhousings to the T90 three-speed, as was the popular transmission found in 1946-1971 Jeeps.

Product & Features

Block_G9N
Block_C1
Block_C3



Options

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. 

The C1 for the T90A transmissions is 2-5/8" thick. This plate style adapter is cast and 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 C3 for the T90J transmissions is 2-5/8" thick. This plate style adapter is cast and 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.

Applications & Compatibility

Engines

These conversion kits will work with most Chevrolet V8s & Chevrolet V6s (Gen. I thru Gen. III+), Buick V6s, the Iron Duke I4, some Chevy I6s and other GM engines.

GM Bellhousings

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. 

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.

Related Products

The BR4 ring is used to enable use of the SM465 5-1/8” bore bellhousing with 4-11/16” retainers.

Block_BR4



LS flywheel 

This is a beautiful piece and necessary for proper operation on LS based engines. They must have the LS crank offset to work properly. These will accept both the 11” and 12” clutch listed below. The page is here with details.

Block_LS400-35X

Bolts necessary for installation

Block_330-2802

Clutch Kit

Many common GM applications used the 10 spline 1-1/8” hub and as such, it is usually a matter of selecting the correct version. Three sizes are listed below. Most common is the 11” listed in the middle but all are serviceable depending on your needs. Generally the 10-1/2” is used on the smaller 153 tooth flywheel and is exclusive to that application. The 11” and 12” are usually interchangeable with large bellhousings and standard 168 tooth flywheels. Non-standard applications will need to watch for compatibility.

Block_04-021



The disc can be purchased separately for those applications natively using a different spline count

Block_CD4187

Block_CD4025

With the G9N kit, one of the following clutch discs will be required:



Adjustable release bearing 

While sometimes not needed in this application, it is priceless when clearances dictate its use. You may get lucky and find a correct height release bearing but this product will guarantee correct height when set up properly. Further information is here.

While sometimes not needed in this application, it is priceless when clearances dictate its use. With all the variabilities in flywheel and clutch height, we highly recommend its use. Further information is here.

Block_TB1

And adjustable pivot is an additional noteworthy option allowing even more flexibility to this critical setting.

Block_3855G

Bellhousings and adapter rings

Most stock bellhousing will work with the GMAX15. Large 5-1/8” bore versions require a ring to adapt to the 4-11/16” size of the GMAX15.

The BR4 ring is used to enable use of the SM465 5-1/8” bore bellhousing with 4-11/16” retainers.

Block_BR4

If you need a bellhousing, would prefer a new enhanced casting version or would like the LS specific version they can be purchased here:

Chevrolet pattern, Gen I & II small 4 ­11/16” bore


Chevrolet pattern, Gen I & II large 5­ 1/8” bore


Chevrolet pattern, Gen III & IV small 4 ­11/16” bore


Chevrolet pattern, Gen III & IV large 5 ­1/8” bore


Clutch Release Arms

A proper release arm for your application will be necessary. Several choices are available.

This release arm is the best choice of release arm for a GM engine swap in 1945-1971 CJ models. It's proper length gives the correct release action for GM clutches, and is compatible with the early bellcrank linkage systems found in these earlier Jeeps.

Block_RAV6

This release arm is the best choice of release arm for either a GM engine swap in 1972-1986 CJ models, and some FSJ Jeeps - with the factory mechanical release system (not hydraulic). It's proper length gives the correct release action for GM clutches and is compatible with later rod & bellcrank linkage systems found in these Jeeps.

Block_RAGM

This release arm is primarily for GM hydraulic release applications. It is the proper length to give the correct release action with hydraulic linkage systems found in Jeeps YJ, XJ and TJ Jeeps when performing a GM engine and bellhousing conversion, or on some earlier Jeeps that may have a custom made hydraulic system. A modified version of this arm is used in our GM Hydraulic Slave kits HCRC & HCRB.

Block_RAGH

Hydraulic Clutch Actuation

Though not required on all applications, now is an excellent opportunity to upgrade from the likely worn mechanical system. These mechanical systems are usually full of play which is aggravated by years of wear and much more affected by flex in the body/frame relationship, especially when in a twist off-road. You will find that your clutch release point will vary as things twist. With a hydraulic system, that is not the case. All flex is taken up by the braided stainless line which is unaffected by changes in frame to body relationship. If your Jeep has the master cylinder, that part can be reused. More information can be found here. Older Jeeps generally require retrofit of a pedal assembly especially you have a floor mounted pedal now.

Parts to do this swap are:

Block_53004466

Block_HCR8

Block_HCRC-34

Installation Requirements

All of these adapters are easily and quickly installed onto the T90. Full disassembly of the transmission is not required. Cutting the transmission input shaft is not required as the adapter spaces the transmission properly for the GM crank and clutch assembly. The C1 does require the installation of a new input shaft.

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 clutch actuation will require adapting and fabricating either a mechanical linkage from the existing system or retrofit to a hydraulic system. 

Engines & Engine Mounting

mmtj-g3If 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, featuring excellent vibration dampening, superior strength and impressive adjustability - adjustable even after the engine is installed. The design and 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. On a driver’s side drop transfer case, usually the later Jeeps, things often get a little easier as steering and front driveshaft are pushing you the same direction. 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.

Driveshafts

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 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, usually to the detriment of the project. Our recommendation is to always value the correct position of drivetrain components over saving a few dollars which is usually regretted in the long run with compromised positioning. Sometimes the application allows use of the existing shafts without modification. While that is perfectly acceptable, it should not be the first priority. 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. Novak can also accommodate your needs on this if provided with dimensions for the shafts at a reasonable rate.

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