Thread: Flathead Ford trans to OHV motor adaptors

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In times past a fair number of makers produced adaptors mating up the flatty transmissions to later model motors. The adaptors still come up for sale often on e-bay, and once if memory serves, I saw a unit to match something big, like an MEL to a flathead trans.
What are some of your recollections about how the transmissions held up to the increased horsepowers? I am using a 46 3 speed in the 292, and have been treating it like a newborn, over concern about the transmission, even though the trans is like new. The other day I did do a 0 to 4500 rpm burnout just to see what would happen.

Well, here's my take on it. Henry built those boxes to handle a max of 100 horsepower. I don't know what the torque production of the flathead was, but lets get generous and say it was 150 ft. lbs. Can you show me ANY V8 today that would only register 150 on a dyno?

I just looked up acceleration on the old 255 flathead and a 49-53 Merc would do 0-60 in about 16 seconds.

Richard is right, these transmissions will not take the strain of a modern ohv for very long. Sure, you will hear stories of how they ran them on altereds and diggers of the day, but they didn't get many runs out of them. I used to go through so many Chevy 3 speeds that I carried a spare in the trunk!! After a couple of powershifts 2nd gear would lose a few teeth.

There was a reason people ran the early Ford 3 speeds. We had nothing better, unless you opted for something like a Cad-LaSalle, Packard, or similar heavy duty 3 speed. This back to traditional rod craze has guys buying up early ford boxes and rear axles again, to get the look. If you treat it like granny you will be ok, but a few more smokey burnouts and you will be looking for a replacement.


Don

Thanks Don and Tech. Guess I wont be doing any more of those quick takeoffs.

Yeah, smart move. There are lots of cars running similar transmissions, but you just have to keep in mind that your transmission is now 60 years old. Not only has technology changed, but the internals have some time on them. I've seen these early transmissions with the case cracked very badly from gears coming out through the sides.

Don