Thread: flathead tranny

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I just picked up a 59Ab flatty from a 1946 Ford. What years should I be looking for when it comes to transmissions? I like the 3 speeds with the shift lever coming out of the top of the tranny. I just saw a 46 transmission on Ebay and it had the linkage on the side, that's not what I want. I'm hoping some of you seasoned geezers can help me out, thanks.

Hopefully some of the other Geezers can can correct me if I'm wrong, but with one exception I believe the top shift Ford tranny you are describing/wanting were all pretty much unsyncronized.

If you have to ask what unsyncronized or double clutching is you probably dont want one of these.

As far as I know Fords first year for a syncronized top shift tranny was a 4 speed (the syncro-silent) was 1951. It was standard behing the big flat head sixes (F3 and above if I remember correctly) and optional behind the 239 Flathead V8s.

The last year that Ford produced a factory top shift three speed for the flathead was 1939, and this is the preferred one by hot rodders. They had synchronizers on second and third, just not first (the assumption being you only shifted into first when stopped) from at least 1935 and up, perhaps 1932, memory's a little fuzzy on that. The reason folks center on the 1939 version is that it had improved shift fork strenghth over the earlier versions, though they weren't terribly weak. A popular upgrade is to use a gear set from the Lincoln Zephyr (sometimes called 25 tooth, they "drop right in") because of their gear ratio being more favorable to acceleration. These gears are being reproduced by Speedway Motors, www.speedwaymotors.com.

If you use a bellhousing from a '49-51 Mercury you can bolt on later model Borg Warner three speeds which came in Fords, Jeeps, and others. It has a top cover access design, and handily the '39 top cover with shifter bolts right on. Versions of this trans built from the mid '60's will also have a synchro first.

Just to mention another alternative, Cornhusker Rod & Custom makes an adapter to put a T-5 trans that's very popular today. You get overdrive 5 speed, and floor shifter. Read the link, http://www.cornhuskerrodandcustom.net/ytrans.htm
You do have to convert from the torque tube drive also.

Thanks Bob, my area has pretty much been the trucks. (shows huh?)

I'll go along with uncle bob on this one, a '39 box with zephyr gears woud be the way to go.

The gears from a '40-48 Ford 3-spd. will fit the '39 case, so don't turn down one with chipped gears. Keep in mind the pre-49's are all closed driveshaft trannys except truck versions.

Thank you very much gentlemen. Sorry but I'm under 30 so flatheads, double-clutching, and unsyncronized gears fall into the dark arts and black magic area for me but I'm trying to learn. I have a great respect for history and I'm glad you guys are willing to share your knowledge. I also got a perfect 30-31 A frame and half my roadster body from this guy who sold me the motor. He had a bunch of those trannys I wanted laying around including a Zephyr tranny. I picked up some Deluxe roadster Stanchions from him also but that's about the last vintage A stuff he had. He just sold his whole lot of parts/cars: a bunch of frames, axles, banjo rearends, 4 or 5 model A truck cabs V-8 flatheads, Strombergs, a nearly complete 34 Ford truck, Model A doors, cowls, you get the idea. He let it all go for $1,500. I wanted to cry. He's the second guy I bought parts from that said they had parts for an open driveline conversion. Can someone please explain this to me.

Okay, going to assume you're not familiar with the stock pre-49 passenger rear ends. Rather than the open drive shaft you're likely familiar with from more contemporary cars old Fords used an enclosed drive shaft from the trans to the rear end. It was enclosed in a housing that swiveled at the end of the trans, and bolted "solid" to the rear banjo, it is refered to most often as a torque tube since it limited the rotation of the rear end from the effects of torque. Ford wasn't unique in the use of these as Chevrolet, Buick, Olds, and others employed them too.

If you use the pre-'49 trans it will accomodate the torque tube. If you use one of the other transmissions mentioned, they use the more conventional open drive with the splined yoke to allow for movement in front, and exposed universal joint in the rear.

For early Ford type setups you can get an open drive rear banjo unit from a 42-7 Ford pickup. Or there are after market units made to do the same thing; http://www.hotrodworks.com/Openconv.htm
If you, or someone you know are a good machinist this should give you inspiration, otherwise it is a decent graphic to put a picture to these words.

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

Flat head Ford transmissions in general, were pretty weak sisters, as transmissions go. Back in 66 or 67, I had a friend John Donald who owned a very mildly modified 53 Ford sedan with the original flathead. One summer John and I used up every transmission out of every wrecking yard in a 50 mile radius of Stirling, Ontario. We got so good at changing transmissions in my dads driveway, that by the end of the summer we could change one in about 20 minutes.
That was in the "heyday" of midnight drags, power shifting, cruising the drive-ins, and "chirping the tires on a shift into second gear" on the main drag, if you knew the town cop Charlie Bang Bang was busy at the other end if town.
Finally, John got rid of the car because it was becoming impossible to find a transmission within a one hour drive of home!!!!

IIRC, a '49 pickup bellhousing (rear part) has the same pattern as an early toploader fourspeed. (Or an overdrive toploader, too.) The pickups used a two-piece bell, which adapted the '49 style engine to the earlier short bell.

Again, thank you guys very much. I have seen the banjo rearends with the torque tubes and wishbones. I've just never had a chance to get underneath a complete driver with a closed driveline to check it out. My engine has the bellhousing cast into the block so I guess I'm kind of limited as to what transmissions I can use. I've even heard of guys using C4s behind their flatheads. Right now I'm in the collecting stage. I have an original frame, a motor, and a 40 Ford front suspension. I'm only half way done with my channeled and Z'd 30 roadster, so I can't get too far ahead of myself with the next project. But I bought a book on building a traditional AV8 and that's how I'm going to build the next one. Thanks a ton.

I'll add my caution against abusing an early Ford three speed. I had a '51 with a stout built flathead, and busted a lot of trannys - got real good at swapping them out, and fixing the ones that were fixable. I always broke them on the shift from first to second, when I'd step (pop) the clutch in a power shift. If you treat them civilly, they'll work well.