Over the years, I know you have had all these transmissions in your cars, so that is why I am asking you what you would recommend, and the pros and cons.
Ian Hackett
Via the Internet
A. I've got to put things in perspective here-you've asked for an opinion, so here it is. As much as I love old-time stuff, particularly Flatheads, I wouldn't build a car today for long-distance cruising with a '39 box. We've had them behind Flatheads, small-block Chevys, and even an early Olds, and while they held up reasonably well when driven gingerly, they could just as easily be blown into various-size chunks with judicious use of the loud pedal. When those boxes were a dime a dozen, and I didn't mind lying on my back in the driveway to change one, scattering the internals of a transmission was part of being a hot rodder. But today there are better uses of my time than fixing broken transmissions, and there are better transmissions than a '39 to put behind a Flathead.
At this point I have to confess to resisting T5s on principle until recently; I just couldn't bring myself to put a modern-looking transmission behind a Flathead. However, my opinion has changed. Recently my long-time, hardcore rodding buddy replaced the '39 box in his Flathead-powered '29 with an S-10 T5, and the difference in the car is nothing short of amazing. The gear spread is perfect for the engine's torque curve and with a low First gear and overdrive Fifth, the roadster is equally at home creeping in city traffic or flogging down the freeway.
Keep in mind, T5s are available in two versions: the later versions being referred to as the World Class design. The most common T5 donor vehicle is a four-cylinder, '83-87 Chevy S-10 pickup. While this is a lighter-duty transmission, the non-World Class is strong enough for a Flathead, the shifter position works well, and they have mechanical speedometer drives. On top of all that, they are affordable, compact, and an easy swap, so what's not to like? The only thing better would be a five-speed that looked like a '39 box. As for the top-loaders, they are great transmissions and the overdrive three-speed is an interesting option; however, it obviously lacks the gear spread of the five-speed. Another popular option is the C4 automatic conversion, and while they work well, some do draw the line when it comes to putting an automatic behind a Flathead, and again, no OD.
Of course, there are some other options. I have a '50 Mercury overdrive three-speed behind a Flattie (they bolt directly to a 59A block), and while Ford and Merc overdrive three-speeds can be found to hang behind early or late Flatheads, you'll have to use a column shift, or a floor-shift conversion, either of which complicates installation. All things considered-cost, availability, and drivability-the T5 is hard to beat. And several of our advertisers offer affordable kits to install them.
**Note: This Is Just A Letter From A Reader, Not A Q&A**
Cheers To You, Mate
G'day, when going out to buy an engine, or a car for that matter, that had a variety of stroke lengths for a given block, how do you tell the difference when they look the same externally? Here in Australia, the Ford 351 Cleveland had a little-brother 302 Cleveland, which was a factory destroked 351C, using a 3-inch stroke crank (instead of 3.5 inches) and longer con rods, and was used as the base engine choice when ordering a V-8 car. Some unscrupulous people try to sell the 302C as the more preferred 351C engine you can't tell the difference because from the outside, especially since the internals are interchangeable.
You can quickly check to see what size engine it is you are really looking at with an electrical cable tie (zip cable) and using the following method:
1. Remove a spark plug.
2. Disconnect the coil to distributor high-voltage cable.