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Chevy Bellhosing

The Novak Guide to the

Adapting Ford Style Transmissions to GM Engines

No adapter for the classic GM engine bellhousing (with the Muncie / Saginaw bolt pattern) to the Ford transmission is required. With a few simple and cost-saving modifications, 1966 and newer Ford T18, T19 and Ford NP435 transmissions (and others) can be used with most GM bellhousings, including full-circle or open-bottom types. Using this method will also allow you in the future to remove the transmission without having to remove the bellhousing like you would with some GM applications.

This works with classic Chevy Small Block, Big Block, Buick and GM Gen III+ engines. For Chevy & LS / Vortec applications, use of a classic Chevy "621" style(#3899621) bellhousing and its modern LS variants is recommended. See Related Products, below.

A warning: you must achieve precision centering with your transmission to bellhousing! It is never acceptable to use only the transmission to bellhousing bolt holes to locate the transmision on center. Also, the retainer provides a critical shouldering function when the powertrain is under torque. Failure to adhere to this will turn your transmission input shaft, pilot bushing and mainshaft needle bearings into a u-joint and wallow them out, leading to an expensive transmission failure.

While on this topic, we strongly suggest you dial in your bellhousing to your engine to verify that it is truly on center. Many transmission failures are due to incorrectly machined bellhousings or blocks from the factory. This procedure is outlined here.

The Procedure

Bearing Retainer Modification

Ford T18 Retainer Modification

For the first step the services of a machinist are required. The front bearing retainer from the Ford transmission is removed and lathe turned down around the large diameter to where it will be a 0.004" to 0.005" slip-fit into the bearing retainer hole in the back of the GM bellhousing. Take an accurate measurement (and with the proper tools - calipers work best) from the hole in the bellhousing before doing this. The small diameter of the Ford bearing retainer is also machined down so it will slip-fit the GM clutch release bearing, typically to 1.371" diameter. Next, the retainer snout is then shortened by 7/16" or 0.437".

Large Bore Bellhousings

If using a GM bellhousing that has a 5-1/8" bore, you will require a sizing ring be pressed onto the flange of the retainer. Failure to properly center and shoulder the transmission on center will ruin your transmission. See Related Products, below.

Transmission Front Face Bolt Holes

On the front face 1966 and newer Ford four-speed transmissions, the upper two mounting holes are each about 1/4 of a bolt hole off from the upper two holes in a GM bellhousing. If the holes in the Ford transmission ears are filed to be slightly elongated, they will match up with their mountings to the GM bellhousing. It may be recommended at this point that you test fit the transmission to the detached bellhousing, which will facilitate the next step.

On the lower front face of the Ford transmission are two ears that, if stock, are undrilled. The lower left ear can be drilled to easily match the hole in the lower left of the GM bellhousing. The right ear can then be drilled. It will not meet up with any hole in the GM bellhousing, so it is necessary that you drill and tap one to match. Use the same size bolt as you do for the other three. If you are not equipped with the tapping tools or the disposition to tap a good, clean set of threads, you may take this to a machinist as well.

T19's & NP435's Without Extra Ears?

NP435 front face without extra ears

If the New Process 435 or T19 being used does not have the extra lower undrilled ears on the case it can still be used with a GM belllhousing using the following procedure:

  1. Do the machine work on the front bearing retainer as described above
  2. Install the retainer and front bearing on the transmission case using 5/16-18" x 7/8" long socket head screws
  3. The two upper holes in the transmission case will be elongated as described above
  4. Bolt the transmission case to the bellhousing with the two upper bolts
  5. Attach the brackets provided in the Novak kit #F2GM (shown, below) behind the Ford transmission flange
  6. Bolt through the brackets into the GM bellhousing lower holes

While the above is more involved than using a transmission that has the extra blank ears, it is about the only option available if the transmission does not feature them.

Hydraulic Clutch Release Upgrade

Many installers consider upgrading to hydraulic clutch release while peforming these other related upgrades. Novak can provide our popular #HCR series slave cylinder retrofit kit for a variety of Jeep and powertrain combinations. Read more about these.

Related Products

GM crank to Ford pilot bushing

Bushing, pilot, GM Gen. I-III (1955-2000) cranks to Ford T18 & NP435 transmissions, #PB-3901176

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.

LS Vortec Gen 3 crank pilot bushing to Ford

Bushing, pilot, GM Gen. III cranks to Ford T18, NP435 & Jeep T150, T18 (1976-1979) transmissions, #PB-6071176

This pilot bushing is for Ford transmissions to most Gen III+ crank flanges, with the exception of some earlier truck 6.0L & 4.8L versions, as discussed here.

Modified T18 Retainer

Retainer, front input bearing, Ford T18 & T19 transmissions to GM bellhousings, #T18-6-GM

This is a new T18 cast-iron retainer that has been machined to GM bellhousing specifications; useful if you don't have a local machine shop to machine your existing retainer, or if the existing retainer is cracked, which happens too often during salvage handling.

Retainer, front input bearing, Ford NP435 transmission to GM bellhousings with the 4-11/16” bore, #WT291-6GM

This is a new T18 cast-iron retainer that has been machined to GM bellhousing specifications; useful if you don't have a local machine shop to machine your existing retainer, or if the existing retainer is cracked, which happens too often during salvage handling. If ordering an NP435 rebuild kit or front bearing at the same time, we'll press them together for you.

Ring, bellhousing register, 4.68” to 4.85”. GM small bore to Ford and Jeep, #BR4-5

This ring presses onto the factory diameter Ford retainer when using a large bore (SM465 style) GM bellhousing.

Novak #F2GM Bracket Kit

Kit F2GM, brackets, adapting Ford NP435 & T19 transmissions to GM bellhousings, #F2GM

These brackets as described above are for NP435 and T19 transmissions that don't have the extra ears required for fastening to the bellhousing. They come zinc plated and pre-assembled. Fasteners and dowel pins are included.

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.

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.

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.


Summary

While it is simpler to join GM bellhousings to native transmissions such as the SM420 & SM465, it is still popular to join up Ford transmissions for the sake of specific gearing needs, preferences and just having a good Ford transmission on hand. If you have any questions about this procedure or wish to make a contribution to this article, please let us know.