Powerglide: A GM’s Greatest Hit Or Deadly Sin?

(first posted 3/30/2012. Revised 6/11/2017)    Or some of both? All depends…among other things, whether we’re talking 1950 or 1973. Powerglide was the first automatic transmission available on a low-priced car. As well as the last of its kind almost a quarter century later. Yes, the Powerglide’s longevity was legendary, both in terms of its three decades of utilization, as well as its durability. And before we complain about its two-speed-ness, let’s keep this single thought in mind: it started out as a one-speed.

Well, strictly speaking, it had two speeds, but it didn’t shift automatically between them. The Powerglide was of the “slush-box” school of thought regarding automatics, unlike the four-speed Hydramatic used by Olds and Cadillac, which didn’t have a torque converter at all, but a fluid coupling, hence the need for four gears.The Hydramatic was efficient, but it was not very smooth. And although it was a brilliant breakthrough, GM’s engineering staff was also interested in exploring the alternative approach to automatics: torque converter.

A torque converter can be set up for a very wide range of effective “gear range”, and the appeal of the torque converter was that it didn’t require any “gears” at all; the necessary torque multiplication could all happen in the torque converter (“TC”). One needs to see these TC transmissions in a different light: not as an automatically-shifted gearbox, like the Hydramatic, but as a seamless way to transmit the engine’s power to the wheels. TC drive was being used extensively in military vehicles, buses, locomotives, and other heavy equipment due to the great attraction of eliminating the cumbersome mechanical drive and clutch. It made for a very smooth power delivery.

That was the appeal to GM as an alternative to the jerky Hydramatic. Buick bought into the concept first, with its Dynaflow, and Chevy soon followed. The Powerglide was very similar to the Dynaflow in design and execution. of course that meant leisurely take-offs, which was helped a bit by the fact that early Powerglide Chevys always slightly had more powerful engines teamed up with them. But in 1950, traffic was invariably leisurely, and the PG’s smooth delivery was a very acceptable trade-off. It’s hard to overstate what a relief it was for many drivers to be able to give up the clutch and manual shift.

It was a complete drive-train package, with an up-rated 105 hp six that sported hydraulic valve lifters, and a lower (numeric) ratio axle to help compensate for the mileage loss. According to an extensive survey of owners, PG had an average 1.5 mpg fuel economy loss.

Of course, the original PG could be shifted into Low manually, for grades, as well as snappier take-offs, up to a maximum  of 40 mph. That manual shift could be harsh, and hard on the transmission, so beginning in 1953, PG got automatic shifting between first and top gear. Progress. Or faster progress.

The first generation Powerglides had cast iron cases, built into 1963. Starting in 1962, the aluminum case PG superseded it, in part because a lighter version for the Chevy II was a necessity. There was also a HD version of the aluminum box PG, which has become immortal as a simple, efficient and rugged two-speed drag-racing box.


The PG would shift into top gear depending of course on rear axle ratios and the engine’s rev range. The highest tested shift point was 76mph, on a ’63 409 (340 hp) Impala coupe, with a standard 3.31 axle ratio.But according to my calculations, a 1967 Corvette 427 with PG would not shift into high until about 90mph, or more.

A typical mid-late sixties 283 equipped big Chevy would shift at between 50-55 mph. Therein lay the Powerglide’s shortcoming. Cars were getting heavier, speeds higher, and expectations were being raised, especially by Chrysler’s excellent three-speed Torqueflite and the improved Ford C6 and C4 three-speeds.

Below is a brief excerpt from a 1965 Popular Science test of 1965 full size cars, including a 352 equipped Galaxie, 318 Fury, and 283 Impala. Admirably, the Chevy was the lightest car of the three, but that wasn’t enough to overcome its handicap of no intermediate gear, and delivered the longest acceleration runs and the worst fuel mileage. Here’s how PS summed up the issue:

The result was a 12.8 second run to sixty and a 14.9 mpg mileage. That the 352 Ford eked out a better mileage number (15.8) is testament to the reality that when even a more efficient engine has to run harder, in less efficient engine speed ranges, it will use more fuel. The Chevy’s V8/Powerglide power train was top dog in 1955, but ten years later, it was showing the strain of time and changing expectations.

Sure, it was immensely reliable, which is undoubtedly why Chevy stuck with it after their disastrous 1958 Turbo-Glide crash. But by 1970 or so, when cars were burdened by ever more weight and accessories, it was undeniably past its sell-by-date. The modern Turbo-Hydramatic started becoming available, initially only on the new big-block motors, starting in 1965.

1971 was the last year for the Powerglide in the large Chevies; the Vega chugged along for another two more years. Perhaps the ad should say “our apologies to people who expect only three-speed automatics in their Impalas”. I drove a 1971 Chevy taxi, with the 250 six and the PG; it probably had half a million miles on it, so its durability was unquestioned. But man, was that ever a slow pig….

Legend and slug, all in one. So what does the jury say?


Related reading:

1967 Corvette 427 Tri-Power PG: The Ultimate (and Fastest) PG Equipped Car Ever

Two Speed Automatics vs. Three Speed Manuals: When 2=3, More or Less