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

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 bullet-proof-ness. 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. A torque converter can be set up for a very wide range of effective “gear range”, and the PG, along with Buick’s Dynaflow, went that route. 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.

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 rough 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 Starting in 1962, the aluminum case PG superseded it, in part because a lighter version for the Chevy II was a necessity.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. 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?