Bob gave an excellent answer already except for two points. First the Ford three speeds are not overly strong and if you build up the engine, especially with a Merc 4" stroker crank, it will be easy to chip gear teeth in low gear if you just floor it in low gear. This can also be done with the 3 3/4" standard crank shaft version as well. With a 3.78:1 rear gear the acceleration in low gear was a lot of fun except it could chew up tires and trans gears. Perhaps it has to do with the age of the driver but I went through three transmissions in about one year with just a mild rebuild of a 59AB when I was a teenager. You will know when you have done it when in low gear you get a loud "tick tick tick" in low gear. The chipped tooth is not the problem in itself, it is the question of where the little piece of tooth goes next in the inside of the trans!

Second, if you look at any original Ford from '28-'48 (boy are those numbers nostalgic for me, "Ford '28-'48") you will notice a closed driveline "torque tube" which was a tube from the back of the trans to the front of the rear enclosing a splined drive shaft and it even had a zerk fitting so you could pump grease inside the tube for lubricating the shaft. The only universal joint is/was at the rear of the trans with the drive shaft fitting into a splined end at the front of the rear. When everything was new it worked fine but as the universal wore a little, the clutch wore a little, the pressure plate relaxed a little in the spring tension and especially as the throwout bearing wore, a HORRIBLE situation developed when you put it in reverse and eased out the clutch: the whole car would BUCK violently, so called "clutch chatter"! This was especially bad in a convertible which had a more flexible frame but even a Tudor would buck violently in reverse if the throwout bearing was bad. I tell you this because I had a 1947 convertible in which I avoided reverse at all costs! Now in a modern open drive line the drive shaft has two universals, one at each end and you can see the tube rotate. Now if the universal needle bearings are worn you just hear a "clank: when you put the automatic trans in reverse as the slack is taken up but not the bucking. The good news is that you can keep the old rear end and buy a kit from Speedway to adapt an open drive shaft to the old closed rear but most folks just swap in a modern rear and then you have to use a modern trans or get an adapter for the transmission. However the main thing if you keep the original driveline (which millions used for years) is make sure you replace the throwout bearing, clutch disk and pressure plate as well as maybe slightly resurfacing the flywheel face to make sure it is flat. There were also kits available from Pep Boys at one time which had two threaded rods alongside the transmission to firm up the whole driveline. Having said all of that, if I had an original '41-'48 Ford I would keep the stock drive line and just replace all the clutch parts rather than replace the rear, but if you put even a mild SBC 265-283 in front of that Ford transmission with a simple adapter plate that are still available, the stock transmission will not last long. That is why folks adapted Packard and other heavy duty transmissions to built up flatheads and when the first small block Chevies were adapted to early Fords. Anyway I wish I had a '41-'48 Ford but since I couldn't find one I am building a 'glass '29 and hope to have fun with a SBC, GM trans and a Ford open drive 8" rear.

Don Shillady
Retired Scientist/teen rodder