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Adapting a T5 to a Ford Flathead V8

By Jason
5 months 10 days ago

So you’re ready to make that upgrade to the T5? Completing the swap can certainly raise some questions when it comes time to select the right parts for the job. There are a number of things to take into consideration, but with a little help from Speedway, we can make the process a little more pain free.

The Beginnings

The first T5 five-speed transmissions were originally manufactured by Borg Warner as early as 1982 and continued production has since been taken over by Tremec. Due to the abundance of availability and variety of interchangeable parts, the T5 is one of the most popular American-made standard transmissions among rodders today, following its predecessor - GM’s four-speed Muncie. The T5 offers gear ratios that are a great match for most Flathead vehicles, especially gaining the fifth-gear overdrive.

What T5 should I use?

A great option would be picking up a T5 from a Chevy S10 or GMC Sonoma pickup between ’82-'92. One advantage to using a T5 from a pickup is the shifter position was close to that of the old Ford top-loader. The T5s used in Camaros had shifters designed to sit at an angle. Typically the earlier T5 transmissions used mechanical speedometers while later models used electronic speedometers, therefore it's a good idea to keep in mind what gauges will be used.

As the hunt for a quality used T5 is becoming more difficult, Speedway offers an alternative option from Tremec, the TKO five-speed, which is designed with multiple shifter locations to work with a variety of applications.

How to identify a T5

There is one positive way to identify a T5 which is by locating the metal tag bolted to the tail-housing of the transmission. After you’ve identified the code, there are many useful TAG-ID sites that can be found on the web. Another good way to identify a suitable T5 candidate is by looking at the input shaft. Most of the S10 and Sonoma transmissions will have a 1-inch 14-spline input shaft. Camaros often used a 1-1/8-inch 26-spline input shaft. Common Ford transmissions used a 1-1/16-inch 10-spline input shaft.

The Adapters

A First things first, let’s take a close look at the adapter. Depending on the application, Speedway offers two options: the (left) 916-28914 and (right) 916-28912 (also matching alternatives from Offenhauser).

B Both options will adapt any ’32-’48 Ford and Mercury Flathead V-8 flawlessly, but note that later Flatheads like the ’49-’53 Ford and Merc 8BA engines will need a factory 3” bellhousing adaptor, found on '49-'52 Ford 1/2-ton pickups and '49-'50 Mercs. This also requires a matching starter plate or cover assembly to mount the starter.

C/D The major difference between the GM-style 916-28914 photo C and Ford-style 916-28912 photo D is how the clutch and release assembly will be used with each. The 28914 is machined with a large window to accept the updated GM-style clutch release fork and release bearing assembly (PN 916-29510). The 28912 is designed for use with the original Ford arm, release shaft, clutch fork, and bearing, which is a perfect option if you’re using it with an original chassis and pedals.

The Flywheel

E The clutch and release assembly will affect the choice of the flywheel. If you’re using the GM-style adapter, the stock Flathead flywheel will need to be drilled to accept the GM-style pressure plate. Or you might consider a matching flywheel from Speedway like PN's 910-15627 ('32-'48) or 910-15629 ('49-'53), drilled to accept both Ford and GM-style pressure plates. If you choose the Ford-style adapter on ’32-’48 engines, the original flywheel requires no modification if it uses a stock 9 or 10-inch pressure plate. But an 11-inch flywheel will need to be re-drilled to accept the smaller 9 and 10-inch pressure plate assemblies. Also, ’49-’53 engines will require the use of a ’40-’48 - 9 or 10-inch pressure plate and may require the original flywheel to be re-drilled to match.

The Pressure Plate and Clutch

F If you’re using a GM-style bellhousing adapter, you’ll also need to use a Chevy-style throwout bearing along with a diaphragm style pressure plate. The diameter of the Chevy-style release bearing is too small to work with a Ford-style pressure plate assembly. One option commonly used with a GM-style adaptor kit is the 10-1/2-inch diaphragm style pressure plate like PN 910-15637. Then all you’re left with is matching a clutch with your pressure plate/flywheel assembly and input shaft. If you choose the Ford-style adapter, it requires the use of a 9 or 10-inch ’40-’48 Ford-style pressure plate and matching T5 clutch disc. The Ford adapter also requires a ’32-’48-style throw out bearing and collar assembly like PN 910-25620. Because there is a bellhousing interference issue with all 11" pressure plates and '49-'53 9.5-inch passenger car pressure plates have internal engagement finger interference it is best to avoid using these parts.

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