What made the Chevy Powerglide transmission so special? – Jalopnik

The Powerglide transmission used in Chevrolets and some other General Motors cars was introduced in 1950. While it wasn’t the first automatic transmission, its simple design made it an affordable option for a wider range of car buyers.

The first generation Powerglide transmissions, produced until 1962, had cast iron housings connected with bolts and gasket joints. Overall, it was heavy, prone to leaking fluids, and its two-speed operation earned it the nickname “slip-and-slide Powerglide.” Although it had two forward gears, until 1953 it started from a standstill in top gear, taking its mechanical advantage from the torque converter and only shifting to a low gear to negotiate steep hills.

It was the second generation of the Powerglide, in 1962, that made it so special: a virtually indestructible transmission. Until it was discontinued in 1973 and replaced by the Turbo-Hydramatic automatic, the updated Powerglide featured an aluminum body that contributed to an overall weight 100 pounds lighter than the original. Its rugged construction and easy two-speed operation earned it a reputation for durability among drag racers, and with available aftermarket parts, the entire transmission is rebuildable and stronger than ever.

Today’s car manufacturers have focused entirely on automatic transmissions with increasingly larger numbers of gears. A major difference between the two-speed Powerglide transmissions and the 10-speed transmissions common today is the large variance between the shift ratios and the small gear ratios.

Two-speed Powerglide automatic transmissions do not have an overdrive gear. Instead, the highest gear ratio, second gear, is 1 to 1 (1:1). While thinking about ratios may bring to mind the pain many of us experienced in algebra class, the 1:1 ratio simply means that the transmission’s output shaft turns the car’s driveshaft one full revolution for every revolution turned by the transmission’s input shaft.

Powerglides intended for use behind six-cylinder engines of the time were equipped with a first gear ratio of 1.82:1, while eight-cylinder versions had a first gear ratio of 1.76:1. The lower first gear ratio of the Powerglide with a larger starting number is counterintuitive. It means that the input shaft has to turn more to complete one revolution of the output shaft: 1.82 or 1.76 turns to be precise. For comparison, the first gear ratio of GM’s 10L80E automatic found in some last-generation Camaros is 4.70:1, with the 1.80:1 fourth gear closest to the Powerglide’s low gear.

Shifting problems are among the biggest complaints about 10-speed automatic transmissions. One factor at the root of 10-speed transmission problems is the complexity of the control modules and internal components. The two-speed Powerglide’s simple operating parameters are its greatest strength. That’s what drag racing teams rely on when building a car. Improved components available through aftermarket suppliers have addressed all the shortcomings of the original Powerglide.

The question is how an outdated two-speed transmission design can outperform a modern 10-speed when both are operating in top form. The answer lies in power delivery and consistency. Modern 10-speed cars use traction control or launch control to prevent wheelspin under acceleration. Neither system actually offers more grip on the tires. Instead, they both work by reducing engine power or, in some cases, using the braking system to prevent wheelspin. And as everyone knows, braking only slows you down.

The Powerglide’s lightweight rotating structure and higher initial gear ratio, combined with the low rear axle ratio often found in drag cars, deliver consistent, usable power to the line’s rear tires. Plus, with its two speeds, the Powerglide only needs to shift gears once during every quarter mile or eighth mile. For a drag car, especially a racer where consistency is crucial, fewer shifts represent fewer opportunities for mistakes that can upset the car and cause loss of traction, resulting in longer elapsed times.