Identifying the best Flathead Transmission

Story and Photos by Zac Parks

Check out more from Zac on his Instagram Account: @wiredcustoms.va

When it comes to a traditional Flathead V8 build, the holy grail of transmissions is either the 1939 Ford 3 speed or the 1939-1952 Truck three speed. Both are floor shift three speeds, the large trucks had a 4 speed floor shift but the gears are unsynchronized and the gear ratio is terrible for a Hot Rod. I am going to show you how to identify the two transmissions so when you go to the swap meets you know what you’re looking for.

The first problem lies with the overall appearance, 1932-1939 car and 1939-1952 truck transmission case look extremely similar, but only a few in that bunch will build a good Hot Rod.

So let's cut right to the chase and give you the most valuable information first! Ford actually serialized the cases unlike the motors of the time. This serial number does not correspond directly to the VIN of the vehicle, but rather indirectly in that this serial number was only used within certain timeframes and years.

1932-1934: 18-7006

1935-1936: 48-7006

1937- Infamous 78 series case was introduced 78-7006

The 78 top loader case is the best case to have, it will take the larger clutch and pressure plate, and internally the bottom of the case is deeper, capable of clearing the 29 tooth cluster gear. Below you can see where to find the case number, the beginning part of the serial number before the dash is the most important information.

Outside from the case, a lot of parts can be interchangeable between the above stated cases, an early case that's non synchronized 1932-1938, could have the later synchronized gear sets but needs a lot of modifications to do so, that's why the 1939 and later three speed top loaders are so important.

Next important piece you will need is the 1939 car or 1939-1952 Truck shift tower. These will have a double detent and will help to lock the transmission into gear, a lot of the earlier cases without this era detent will pop out of gear during acceleration. Below you can see me pointing out one of these detents, then the second picture showing both detents, one on each side of the shift tower.

Now since these transmissions are so old, a lot of the crucial parts could have been interchanged just to keep the vehicle on the road. The next important detail you need to look for is the synchronized 2nd and 3rd gear. On all gear sets 1st will be unsynchronized. Below you can see me pointing to the brass synchronizer ring itself, take a good look at this setup, on a non synchronized transmission there will only be one set of synchronized teeth on either side of the synchronizer hub and not 4. You’ll be looking for 4!

Last but not least, you’ll be looking for the correct transmission mount. This will be solely for the application for which you are buying the transmission, but I would like to show you what the 1939 trans had originally. Below you can see the ears on the 39 case, make sure these are not cracked or broken, very typical for them to crack. Second picture below shows the truck style trans mounts, they are a little stronger than the 39 mounts.

From my experience and experience of the Hot Rodders before me, these transmissions are the best for traditional Hot Rodding. Lincoln Zephyr gears should be noted as one of the best as well but are much harder to get a hold of and expensive nowadays. But let's not give the wrong impression, these transmissions are getting pretty pricey, a professionally rebuilt top loader three speed are going for $900-$1,100. It's in your best interest to find a good candidate for a rebuild and rebuild it yourself, a worn case with bad internals could cost up to $1,000 in part cost alone. The good news is, all the gears are being reproduced and can be replaced, and if you have all usable gears then a rebuild kit itself is going for $200. So take the time to find the right one for you and get in the garage and Get Your Shift Together!