Q: I have a 1973 Mustang fastback that I have restored with the help of parts from Summit Racing. It has an FMX transmission, which I would like to swap for an overdrive automatic. Is this possible? Can you tell me which AOD four-speed will hook up to my 351 Cleveland engine?
A: We hate to be bearers of bad tidings, but the AOD is not the best choice for you. There are three reasons for this. In our opinion, a stock-form AOD can’t handle the torque your 351C produces. Then there is the flywheel — the balances between your 351 and an AOD-equipped 302/351W are different (28.2 ounces for 351 up to 1980, 50 ounces after 1981).
That said, we’d suggest using the C-6. While it doesn’t have an overdrive gear, it is strong enough to handle your engine.
(Editor’s Note: Our post originally stated the diameter of the AOD is too small to fit the Cleveland. However, the 351W and 351C share the same bellhousing, allowing the AOD to be mated to the 351C by using the pre-1980 flexplate. We apologize for the oversight.)
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