flathead transmission swap

Dan1234

Dan1234

Member
I have a 1950 Ford Flathead v8, that I would like to change over to a modern auto transmission. Just wanted to get some good input on this.
 
Normaly you can't beat a C4 from the 60's-70's, it's just a 3 speed no lock-up plain jane trans. Speedway offers a kit, some assembly required, good luck Chuck S.
 
If you want over-drive I would go with an AOD. One issue with the AOD is the size, it is a lot bigger than the C4.
 
Another thought: If you go yo the C4 you;ll need to change the rear axle ratio. Wuth the AOD you don't.
 
Ol' Ron said:
Another thought: If you go yo the C4 you;ll need to change the rear axle ratio. Wuth the AOD you don't.
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Ron, I'm real curious about this, I would think that you would have to change the rear ratio with the AOD, not the C-4. I just did the C-4 to AOD and when the AOD goes into 4th, it really drops the RPM's so I've been thinking of going to a lower rear ratio. I'm running a 3:50 rear gear now, the RPM's are at 1700 at 70 MPH. How much would a 3:73 ratio raise the RPM's, do you think? I hope that I'm helping with this question to answer the original guys question. Thanks Ron for any help, I respect you guys opinion a lot.
 
One of the advantages of an OD is you can run lower rear end gear ratios. You could even run a 4:11. This improves acceleration considerably, BUT as Ron has stated on several previous post he is currently interested in maximizing fuel economy, not acceleration. The 3:50 gearing should help in the MPG area.
 
If the rpm drops to low at cruise, like matey's 3.50 rear and an overdrive, it can hurt mpg surprisingly. My preferred choice would be 4.11 + overdrive, then you can have your cake and eat it. Good acceleration, better power around town and in the hills and good mpg in overdrive.
All depending on what driving experience you want.
Martin.
 
If you decide to use an AOD trans I wouldn't go higher than a 3.78 ratio. Depending on your engine's low end torque and the low gear in the AOD trans that 3.78 ratio should give you a decent bump off the line and better mileage than a 4.11 at higher speeds. As a frame of reference the 86 Ford Bronco AOD trans with a .67 O/D reduction came from the factory with 3.55 gears which was the factory's compromise between acceleration and fuel economy. This would be in line with Ol Ron's comment about using the AOD trans with your OEM rear end that probably has 3.54 gears in it. IMO it would be important to decide what you expect from this swap and in that head scratching process factor in the flathead torque curve and its availability to make the other parts of the drivetrain perform to your vision. I'm sure there are folks here on the Barn who have climbed that learning curve and can lend a hand.
 
fortyfords said:
Ron, I'm real curious about this, I would think that you would have to change the rear ratio with the AOD, not the C-4. I just did the C-4 to AOD and when the AOD goes into 4th, it really drops the RPM's so I've been thinking of going to a lower rear ratio. I'm running a 3:50 rear gear now, the RPM's are at 1700 at 70 MPH. How much would a 3:73 ratio raise the RPM's, do you think? I hope that I'm helping with this question to answer the original guys question. Thanks Ron for any help, I respect you guys opinion a lot.
Click to expand...

I have a Dana 60 with 3.73 gears behind an AOD transmission that has a .67 reduction. Tires are 28.5" diameter. At 70 MPH the tach shows a hair over 2200 RPM. Using your 3.50 gear ratio with the RPM calculator the theoretical RPM would be 2022 which for comparison suggests that the difference might only be about 200 RPM increase if you were to use the 3.73 gears.
 
When I chose to use the c4 I bought a 80 Granda 6 cylinder drove it and pictured flathead engine. The car had 2.78 gears and the tire 205/75/15 about the right size for 51 ford. At 2500 rpm you can do 72 mph,22k/63mph,i was getting about 18mpg.
I can climb the hills good and plenty of power. The 8" rear would be good for that car.
 
I just received the AOD kit for my '50 Merc Flathead from Speedway. It includes an AOD rebuilt with special parts and branded as a Speedway Street King. It comes with all the parts and instructions you need for a successful install, including the torque converter. The parts are high quality, in fact, the kickdown cable is supplied by Lokar. The only part not supplied with the kit is the rear transmission yoke, as according to your driveshaft, you may need a different yoke (they're not expensive, however). I intend to purchase a transmission mount Lokar shifter to round out the combo.

Jim
 
Thanks guys, I recieved lots of great input. I should have also mention that I'm running a Ford 9 inch rear. Now the hard part in which way to go. Thanks Again guy's.
 
To some extent it should depend on how you are going to drive it. If only driven occasionally then the C4 (a non-OD) should be fine. If it is driven daily and at highway speeds and/or longer distances then I would want the OD and opt for the AOD.
 
I am installing an AOD in my '53 Ford this weekend after pulling out the 3 speed OD. My rearend ratio is 3.90 (car originally had a 6, no OD) and tire size is 28". This should give me 2195 RPMS @ 70 mph. Perfect for my modified V-8 engine. Here is a handy calculator to play with ratios vs. RPMS, tire size and mph. http://www.crawlpedia.com/rpm_gear_calculator.htm

Having an C5 in my 33 Ford coupe, an FMX in my 34 Ford phaeton, my vote goes for the AOD.
 
expavr said:
I have a Dana 60 with 3.73 gears behind an AOD transmission that has a .67 reduction. Tires are 28.5" diameter. At 70 MPH the tach shows a hair over 2200 RPM. Using your 3.50 gear ratio with the RPM calculator the theoretical RPM would be 2022 which for comparison suggests that the difference might only be about 200 RPM increase if you were to use the 3.73 gears.
Click to expand...

Thanks for that input, I see that I will have to change rear ratio. I do run 31 inch tires so I may have to go to a 4:11 to get about 2089 rpm at 70 MPH. Another guys calculator is a big help.
 
I *** u med you had a stock 50 Ford PU, which usually has a low 3.90 rear, not the 3.54 rear he's got. The above posts answers most of your questions.
 
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