Designed and manufactured by General Motors (GM) from 1963 to 1975, the GMMuncie 4-speed transmission was a manual transmission for longitudinal engine GM automobiles particularly favored with models utilizing higher power engines.
In the mid 1950s, Chevrolet needed a 4-speed transmission for its then relatively new Corvette sports car and did not manufacture its own 4-speeds at the time. Since it was not initially cost-effective to manufacture a 4-speed transmission in-house for a low production vehicle, starting in 1957, GM procured Borg-Warner T-10 4-speeds. Borg-Warner had an excellent reputation for manual transmissions. The T10 itself was based on design plans and U.S. Patent 3,088,336 held by GM engineer James Fodrea. In 1963, 4-speed transmission production was brought in-house by GM and put into production with the introduction of its own standard wide-ratio 4-speed transmission. This new Muncie produced 4-speed transmission was itself a further iteration based upon the highly similar to the T10 with further improvements. As it was produced at GM's Muncie, Indiana factory, it has since become known simply as the Muncie 4-speed. The Muncie transmission featured four synchronized forward gears in the main case with a reverse gear in the tailshaft that had a lockout feature on the selector. The main case was aluminum. It improved upon the T10 design iteration, making it heavier duty with smooth shifting properties. While known for its smooth shafting, the Muncie 4-speed is known was capable of handling higher powered engines with greater torque output of the era. Beyond the Corvette, the transmission was ultimately popularly used in a wide variety of GM vehicles particularly those with higher power output V8 engines. [1] [2]
During the mid to late 1970s, with a greater need for fuel efficiency mileage and resultant reductions in engine power levels, transmission requirements were evolving. 5-speeds were increasingly popular in manual transmission applications. And automatic 3-speed and eventually 4-speed (with overdrive) transmissions were likewise increasingly popular in automobiles. [3]
By 1975, Muncie 4-speed production ended. GM began to utilize other transmissions including 5-speeds, newer automatics and, in some cases, reverted to Borg-Warner 4-speeds for a time.
Over the production years, a number of configuration changes occurred. The countershaft changed from 7/8 inch to 1 inch in 1966. The original 10 spline input shaft was changed to 26 spline in 1971 or 1971[ clarification needed ] depending on model. Finally, the 27 spline output shaft was changed to 32 spline in 1970 or 1971 again depending on model. Generally, later years are considered to have been improved. [4] [5]