Adapting Tremec's Popular T5 5-speed Manual to Ford's Flathead V8 Engine
So you're ready to make that upgrade to the popular T5 5-speed manual transmission? 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, including flywheel and clutch, adapters, and of course the transmission itself. With a little help from Speedway Motors we can make the process a little more pain free by sourcing the right parts the first time. So, read on and see what it takes to put a modern overdrive transmission behind our Flathead when sticking with three pedals.
What Cars Use T5 Transmissions?
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 manual transmissions among hot 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 towards the driver, as did those from the Fox-era Mustangs (though not as severe 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. Of course a GPS speedometer is always an option as well!
As the hunt for a quality used T5 transmission is becoming more difficult, Speedway offers an alternative option from Tremec, the TKX five-speed, which is designed with multiple shifter locations to work with a variety of applications. The TKX has the same, if not better, features as the outgoing TKO series in a more streamlined case. This means less tunnel/floor modifications are required (and sometimes none at all) to accomplish your 5-speed swap.
How Do I Identify a T5 Transmission?
There is one positive way to identify a T5, which is by locating the metal ID tag bolted to the tail-housing of the transmission. After you've identified the code, there are many useful web sites with ID tag databases for the T5 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. We don't have room to get into it here, but many enthusiasts have used the Camaro and Mustang T5s by converting to the S10 tail housing.
What Adapter Do I Need to Mate the T5 To a Flathead V8?
A First things first, lets take a close look at the transmission to bellhousing 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). It is also the preferred option if using hydraulic clutch release components. 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. Note that with the original Ford style linkage you will have to fabricate your own bearing return spring bracket.
Can I Reuse My Stock Flathead's Flywheel?
E The clutch and release assembly will affect your choice of 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), which are 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 you use 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.
What Pressure Plate and Clutch Do I Use?
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 disc 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.
Updated by Mark Houlahan
