The Borg-Warner T-5 transmission is used for this conversion. The 83-88 T-5 found in the Chevrolet S-10 is the preferred choice with a fourteen-spline input shaft and a mechanical (cable) speedometer drive. These transmissions have a tag that is attached to a bolt between the main gearbox and the tail housing with a number on it – 1352-XXX will identify the application (vehicle) that it came from and in many cases will tell you the gear ratios inside for all five gears and reverse. We have found that the 1352-145 is a very desirable ratios that fit the Model A nicely. These ratios, first through fifth, are 3.78, 2.16, 1.42, 1.00, and .072. This transmission is found in 85-86 S-x trucks with the 2.5 4-cylinder and the 2.8 V6 engines. Since these gear ratios have been determined to be the best, check these numbers against any transmission that you find and try to get one that is close to these numbers. You can find a complete chart of the various Borg-Warner T-5s at this website, https://www.britishv8.org/Articles/Borg-Warner-T5-ID-Tags.htm. It’s a great reference.

The other important feature of the S-10 truck configuration is the location of the shifter.  For these trucks, the shifter is as far forward as is possible.  For example, if you look at a T-5 from a Mustang, the shifter is located at the very end of the tail shaft.  That would place the shifter under the front seat of a Model A, which just will not work.  Even with the forward location of the S-x truck T-5, the shifter will be about seven inches back from the stock Model A location.  Shifter location is therefore extremely important.  There have been some builders/fabricators who have made linkages to move the shifter forward on rear-shift transmission, but for simplicity, finding a T-5 with a forward shifter is the best idea.

An S-10 T-5 up to 1996 can be used, but it has an electronic speedometer drive.  There are several options for turning electronic drives into cable, but the “conversion boxes” on the market all run on twelve volts, negative ground.  If your car is still six volts, positive ground (and there is nothing wrong with that!) these conversion devices will not work.  We can supply a cable adapter in the driveline that will allow cable drive to the Model A speedometer, but they can be expensive – several hundred dollars more.  It is better to find a cable-drive transmission.

Finally, you do not need a “World Class” T-5 for your Model A.  These were introduced in 1985 as the Second-Generation T-5 for Ford models and in 1988 for various GM models.  The improvements made to the World Class T-5 were done to allow for more power and torque as engine power increased, particularly in the Mustangs and Camaros.  The non-world-class T-5s can easily handle up to 265 ft-lbs of torque, much more than your Model A Flathead Four will produce.  The World Class T-5 is more durable with the higher power mated to it, but the extra cost is not necessarily justified.  Plus the World Class is generally equipped with electronic speedometer drives, adding more complication and cost.

All T-5 transmissions have die-cast aluminum cases and weigh around 75 pounds.  Mounting features, shifter location and type, input shaft length, diameter and number of splines vary as well as overall case length.  You cannot just go to the junk yard and pick up any T-5 for your Model A conversion – you must get “the right one.”  Think about getting the transmission rebuilt by a reputable shop for years of trouble-free use, too.  Remember that the suggested 83-88 S-10 transmission is forty years old!

The Process – Installing the T-5 with our kit

One common question is “how does this go together?”  Fair enough!

Installation of a T-5 involves removing the torque tube/driveshaft from the car, removing the old three-speed crash box, then installing the new transmission and open driveshaft, then connecting the whole thing to the rear axle.  Sounds simple enough, but it can get a little more complicated than that.

The “Torque Tube”

So why is the driveshaft tube on a Model A called a “torque tube?”  To put it simply, the torque tube encloses the spinning driveshaft, but it also helps to keep the rear axle housing in place.  It also helps absorb the torque transferred back and forth between the engine/transmission and the rear axle.  That is where the “torque” in “torque tube” comes from.  Without it the engine and the rear axle would try to twist each other back and forth.  This concept is used today in such cars as Porsche 944 and Corvette C-5, 6 and 7.

Since we will be changing from a torque tube to an open driveshaft, we must compensate for that loss of support and torque control that we had with the tube.  To do that, the radius arms (rear wishbone) of the rear axle must be strengthened. To do this, you need to understand how the arms are designed – they are hollow with an open seam at the bottom.  To strengthen them, you will have to get the seam stitch-welded to close it up.  This turns it from a rolled piece of steel into a steel tube.  Much stronger.  We also provide 5/8” Heim Joints to properly link the transmission ends of the radius arms to the new transmission mounting.  These joints will allow the rear end to move up and down as needed without compromising strength.

Additionally, we have developed a “Third Link” system that consists of a 1” DOM (drawn over mandrel) and connectors that is attached to the rear end housing and the crossmember just behind the transmission.  This further strengthens and triangulates the frame, power train and rear end to compensate for the loss of the torque tube.