Cruisin’: ‘66 GTO tranny

Q: I own a 1966 Pontiac GTO post coupe with a 389 cubic-inch engine and a three-speed standard transmission. I’ve been told the three-speed manual in my car was made by Ford Motor Co. and used at the end of the model run because GM ran out of four speeds. Is this true? — M.M., Pennsylvania

A: GM never ran out of four speeds, yet the transmission in your car is indeed a Ford-designed unit. The 1966 GTO’s standard features included bucket seats; special exterior trim; a 335-horsepower, 389 cubic-inch, four-barrel engine with chrome valve covers and air cleaner; dual exhausts; and that three-speed manual transmission you speak of.

The four-speed was an option, as was the popular Tri-power three two-barrel setup.According to my records, the standard three-speed manual floor shift in your GTO is called a Dearborn M13 unit.

The four speeds available in ‘66 were a Muncie M20 and a Muncie M21 close ratio. The GM three-speeds were produced by Saginaw, and were also known as Muncie units.

However, they didn’t stand up well to the horsepower and torque of the GTO V-8 engines, so whoever told you that a Ford transmission is in your GTO from the factory is telling the truth.

GM chose this “Dearborn M13” Ford transmission to better handle the power, and from what I’ve seen “FoMoCo” is stamped right on the transmission case. Muncie/Saginaw three-speed manuals were used in light-duty units like six-cylinders and small V-8s.

The GTO would use the Dearborn M13 for years to come. By 1968, Muncie built its “rock crusher” M22, which could stand up to 500 horsepower and was a great tranny.