While looking for the ideal automatic transmission to put behind the fresh roller block 306 Windsor in my 70 Maverick Grand Touring project, I found out it doesn’t exist. This is for a light bodied classic Ford built into a touring car, not a drag strip car. It doesn’t need to handle 1000 horsepower, it needs to handle under 400 horsepower, but it needs to upshift one more time.
There are old-school 60’s/70’s Ford C4 3-speed (“Old Blue” above) and C6 3-speed transmissions that can easily handle the power that require no electronics and the bellhousing bolt pattern is right, but long distance highway driving (that I am setting up the Maverick to do) is not a happy activity for 3 speed transmissions. RPM’s stay high and fuel consumption is much higher than in modern overdrive transmissions.
There are semi-modern 80’s/90’s AOD overdrive transmissions (grey one above) that don’t handle upgraded power well without some mods, but use a mechanical throttle-velocity (TV) cable connected to the carburetor linkage for control and no electronic controller, and the bellhousing bolt pattern is correct for SBF.
There are modern 90’s/2000’s 4R70W overdrive transmissions (below) that can easily handle the power but require electronic controllers costing close to $500 and the bellhousing bolt pattern is wrong.
The solution? Build a hybrid of an AOD and a 4R70W.
The Frankentransmission.
The 4R70 and the AOD use the same style planetary gearset, but the 4R70W has thicker, stronger gears and lower 2.84 gearing for 1st and 1.55 2nd gears, making it feel more powerful behind the same engine, compared to the AOD’s 2.40 first and 1.46 second gears. The thicker, stronger gears can also handle more powerful engines.
4R70W on left with Modular engine bellhousing bolt pattern, AOD on right with Small Block Ford (SBF) Windsor bellhousing bolt pattern:
The plan:
- Use the AOD case with the correct SBF bellhousing bolt pattern that will bolt to the 306 Windsor small block.
- Use the 4R70W planetary gearset with stronger and lower 1st and 2nd gears.
- Use the 4R70W’s wider bands for less chance of downshifting into 3rd, or slipping while in overdrive.
- Use the 4R70W stamped steel drum instead of the AOD cast iron drum for less rotating inertial mass which gives better throttle response.
- Use the 4R70W’s much stronger input shaft.
- Use the AOD’s overdrive with .67 overdrive instead of the 4R’s .73 for lower engine rpm’s at highway speeds.
- Use the AOD valve body for manual control with TV cable.
This would be the ideal classic Ford automatic transmission. The lower gearing of the 4R gearset allows the use of the 3.00:1 gears already in the Maverick 8” rear axle, eliminating the need to do a ring and pinion gear change. I estimate the engine will spin around 2000 rpm’s at 70 mph in overdrive. In a 3000 lb car with 306 small block and a 500 4-bbl cfm carburetor, this should get low 20’s mpg on relaxed long highway trips.
This setup would also be ideal for small block Mustangs/Cougars, any year Falcon/Comet/Maverick, and Fairlanes and Rancheros up to 1971. For bigger, heavier cars from the 70’s, and cars with big block engines, a C6 with an aftermarket overdrive, or an E4OD with a standalone controller would be better choices.
Keep building!
See you on the road!
Dave
Rides-and-drives 