Here is an interesting article by the late Bob Helt about the powerglide transmission. Quite a few common questions we get from PG owners are answered in this piece. We’d like to thank the Lehigh Valley Corvair Club for posting it in their April 2026 newsletter. Enjoy!
Strange as it may seem, the Corvair Powerglide transmission was patterned after the Model T Ford (1908-1928) transmission. Both of these transmissions used a sun and planetary gear set that provided two speeds forward and one reverse. The main difference being of course that the Corvair tranny included automatic shifting between the two forward gears, with the addition of a torque converter that multiplied the low-speed engine torque. In addition, of course, the Corvair Powerglide was simply a slightly smaller version of the Chevrolet big-car Powerglide that had been in production for many years, and was fully developed from Proving Grounds testing and customer experiences. Thus it was that the Corvair Powerglide was an exceptionally rugged transmission that incorporated many of the worst-case fixes made necessary by Chevrolet’s prior experiences.
For example, the Powerglide was designed to be capable of withstanding without failure 100 WOT low-to-reverse shifts on dry pavement. This was to ensure the ability to accept possible customer abuse. (Frank Winchell said that this test was the result of actual driving responses by the public). Of course not every transmission was tested this way. But periodically a production unit would be so tested to ensure that this criterion was still being met.
The bell housing surrounding the torque converter allowed cooling air to be sucked in thru an opening and swirled around the converter prior to being exited from the housing. This effectually cooled the converter and the lubricating oil within. While fairly effective for normal driving, the oil was prone to running at high temperatures when the converter was maximizing the torque multiplication at high ambient outside temperatures. This led to factory recommendations of frequent transmission oil changes.
The torque converter was capable of multiplying the torque a maximum of 2.4 times (later 2.6). This, coupled with the low gear ratio of 1.82:1 gave an effective low speed gearing of 4.36 with the 3.55:1 rear axle ratio. With the brakes firmly set and the transmission in low gear, the 80 HP engine speed was limited to 1600 rpm at WOT. This was called the stall speed.
Although there is no official documentation known, it is believed that later engines were allowed a higher stall speed to more nearly match their torque characteristics. A high- speed lockup was considered (all current production vehicles use a lockup), it was never used on the Powerglides. As a result there was always some slight slippage in the converter even at a steady cruising speed. Maximum coupling was about 94% at 100 Lb-ft torque.
One nice feature, not commonly provided now was the ability to push-start a dead engine because of the included rear oil pump in the transmission. Although, there were slight changes made nearly each year, there are really two different versions of the Corvair Powerglide. One designed for the 140/145 CID engines with their torque capabilities and a second version designed to handle the greater torque available from the 164 CID engines.
This second version transmission used much higher internal oil pressures to counter this increased engine torque. While this later version Powerglide may be installed and used with the smaller engines, it is not recommended that the earlier version ever be mounted to a LM engine because of the lower internal pressures that might allow slipping and loss of power under some circumstances.
There was also a modification to this second version Powerglide that was used for the 140 HP, four carburetor engines, (Powerglide was never available with the turbocharger engines.) This modification effectively raised the shift points to more nearly match the increased speed of the engine.
One might wonder if there were ever any hidden defects or operational problems discovered in the Corvair Powerglides. We can’t think of any but there were a few common failures due to age and wear. These follow. After standing unused for several days, the transmission oil would tend to drain from the converter and settle in the pan. This raised the fluid level to the point that it would leak from a worn or damaged control cable where it entered the transmission, leaving big oil spots under the vehicle.
The fix was to replace this cable or tightly wrap the leaking portion of the cable with an oil-tight covering (available from vendors).
Another possible problem is the diaphragm failure in the modulator allowing transmission oil to be sucked into the engine via the vacuum hose connection. This can be checked by pulling the short coupler hose from the balance tube and looking for a wet condition (i.e., ATF fluid there). This fix was to simply replace the faulty modulator.
In addition, a faulty modulator possibly allowed some uncontrolled shifts that could have broken the e-clip within the valve body. This required the valve body to be removed and a new e-clip to be installed. The broken or lost e-clip resulted in erratic shifting.
Failure of the front oil seal in the differential would allow transmission oil to enter the differential and mix with the differential lube causing excessive wear on the ring and pinion within. This was an infrequent problem luckily. And lastly, the already mentioned factory recommendations to make frequent transmission oil changes due to deterioration of the ATF.
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