Corvair Powerglide
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Chevrolet Corvair Powerglide is a two speed automatic transmission designed specially for the all-new 1960 Chevrolet Corvair compact car that emerged in the fall of 1959 as Chevrolet's competitor in the then booming small car market. Corvair was powered by a six cylinder rear engine that necessitated a specially designed transaxle. Corvair Powerglide took the principles of the standard Chevrolet Powerglide and modified them to suit the rear mounted powertrain location of the new Corvair. Corvair used the Powerglide for all ten years it was produced; 1961-'63 Pontiac Tempest used a modified (for front mounted engine) version of Corvair Powerglide called 'TempesTorque'.
[edit] Operation
Corvair Powerglide is a fully automatic two speed, aluminum case automatic transmission mounted directly to the forward face of the cast iron differential housing. It uses a three element, welded assembly ten inch diameter torque converter mounted remotely on the rear face of the differential, (that also incorporates the starter ring gear, and a centrifugal fan baffle for cooling, via slots in the engine bellhousing) and is driven directly from the engine crankshaft by a flexplate inside the engine bellhousing. No "Park" position is used. The selector quadrant is arranged R-N-D-L. Range selection is via dash mounted selector lever operating a sheathed cable that moves a spool valve range selector in the transmission valve body.
Due to the rear mounted engine, the differential lies between the transmission and engine, so drive to the transmission from the engine is carried forward via a hollow turbine shaft from the engine mounted torque converter to the transmission gearbox. Power from the gearbox was carried rearward again to the differential pinion gear via yet another, concentric, larger diameter hollow shaft. A small concentric shaft inside the turbine shaft operated the front pump of the transmission to permit engagement of drive/reverse ranges when the car was stopped or moving slowly; at speeds over 15 mph, a differential-driven (from the car motion) rear pump of smaller capacity and greater efficiency took over and the front pump shut down to improve fuel economy. The rear pump also permitted the Powerglide-equipped Corvair to be push-started, at a road speed over 15 mph or so.
The Corvair Powerglide provided one reduction range and reverse, in addition to direct drive and neutral. Low and Reverse ranges were a 1.82 ratio reduction, using a single planetary gearset. Locking the planetary geartrain provided a 1:1 direct drive. A multiple disc clutch engaged reverse range, low was braked using a band on the forward clutch drum, and direct provided via clutches. The torque converter of the Corvair offered 2.6:1 reduction at stall, and improved car performance when engine speeds were below ~2000 rpm.
When starting out in Drive range, low gear was automatically selected and the low band applied under pressure modulated by a vacuum modulator which sensed engine output and adjusted clutch and band apply pressures to provide smooth engagement without slip. As the vehicle accelerated, rear pump output would increase and initiate a shift to direct. The rear pump pressures were modified by a throttle valve, and governor, both of which could delay the upshift, or even trigger a forced downshift at driver command. Full throttle downshifts were achieved by the throttle valve which permitted the transmission to stay in low range or be forced into downshifting to speeds between 45-50 mph. At speeds under 35 mph, heavy throttle would delay upshifts, or initiate a forced 'detent touch' kickdown for better performance. When Low Range or Reverse are selected, the apply pressures are not modulated and the full line pressure of the transmission is applied to ensure positive engagement. The multiple plate reverse clutch and double wrap low band design offered a slight buffer to engagement to prevent harshness even under high apply pressures. A quite sophisticated valve body timed shifts and apply pressures carefully in Drive range to ensure smoothness and prevent 'hunting' between gears, which is a common complaint of small cars with automatic transmission. Corvair Powerglide had a good reputation for reliability and was ordered on a large majority of Corvair passenger cars.
Corvair Powerglide was an all-new design, but borrowed a couple small parts from Chevrolet Turboglide and its operating concept is very similar to conventional Chevy Powerglide. Aluminum Powerglide, introduced in the conventional Chevrolet models in 1962 (starting with Chevy II) incorporated many features pioneered by Corvair Powerglide, scaled up slightly for the larger passenger car and light truck lines. The Corvair was originally intended to be only available with Powerglide, but late in its development, a manual transmission was also designed to help lower the base sticker price for its 1960 introduction. The Corvair Powerglide transmission remained largely in its original design throughout the Corvair's production, which ended in May 1969.
The Turbo Hydramatic 350 transmission, which replaced Aluminum Powerglide in the late 1960's was designed with a geartrain layout adaptable to the Corvair and may have replaced Corvair Powerglide had the Corvair line been continued into the 1970's.
