Powerglide Transmission Specs

yellow race car image by goce risteski from Fotolia.com

Introduced by General Motors more than 50 years ago, Powerglide transmissions are still popular among racing and performance streetcar enthusiasts. Through aftermarket transmission companies and car owners who rebuild the original units, the Powerglide has remained in active circulation.

The Powerglide transmission's continued use and versatility owes to the basic specifications of the unit, which allow optimal performance with and without modification.

Basic Specifications

General Motors introduced the Powerglide transmission as a "shiftless" automatic transmission in 1950, later reconfiguring the transmission in 1962 and changing many of the features to those that are desirable today. The transmission became a simple two-speed shifter that included a 27-spline output shaft as well as a manually shifted Muncie M21, which allowed for easy driveshaft modifications. The 19-inch bellhousing, standard in Chevrolet vehicles, made the Powerglide usable in a wide array of General Motors vehicles. While the original Powerglide did not have an oil pan in the transmission, a 14-bolt square pan became standard in models from 1962 and on. The transmission unit measures 27 9/16 inches long, with a face-to-mount measurement of 20 9/16 inches.

Case Style and Dimensions

Another major change from the 1950 and the 1962 Powerglide was that of the case style. Previously a cumbersome cast iron, it was switched to aluminium. This allowed the transmission to be more lightweight, and at less than 45.4 Kilogram, it is this feature that continues to make it popular among racers. The case measures 15 5/16 inches long on both the standard Powerglide and six-cylinder models.

Gear Ratio

The gear ratio of the Powerglide transmission varies depending upon whether the engine is a six-cylinder or eight-cylinder. In the six-cylinder engine, the first gear ratio is 1:82, which is the same gear ratio of the reverse gear position. The second gear ratio in six-cylinder engines is 1:00. Eight-cylinder engines have a lower first and reverse gear than the six-cylinder. The first gear ratio and reverse gear ratio in an eight-cylinder is 1:76. The second gear ratio is the same as that for a six-cylinder, 1:00.


For those car owners who wish to locate and modify or rebuild a Powerglide model from 1962 and after, there are certain identifying marks that will simplify the process. A source code, located on the passenger side of the oil pan, is a combination of letters and numbers. For Powerglides built between 1962 and 1967, these codes start with the letter C, indicating its origin at the Cleveland plant where it was then built, and ending in either D or N. Between the two letters, three to four numbers designate the day and month the transmission was built. From 1968 onward, the source code was altered to reflect the growth in Powerglide plants and so begin with the letters A, C, E, or T. The last letter, which had represented whether the transmission was built during the day or night shift, was also removed.