The Corvair Powerglide transmission

Powerglide transmission with differential

Powerglide transmission with differential

In the photo above, one can see the unique design of the Corvair transaxle. The engine attaches to the differential, which is to the left of the assembly above (the teeth of the ring gear on the torque converter are visible at the far left). The left of this photo would be toward the rear of the car if this were installed inside the car. Thus the differential is next to the engine rather than the transmission as one might expect.

Power is transmitted from the torque converter (or flywheel/clutch in a manual transmission car) through a hollow shaft in the differential on its way to the transmission which sits in front of the differential (at the far right in the photo above).  The transmission transmits its output back to the differential which then drives the rear wheels.

The base model transmission for all Corvair cars was a three-speed manual transmission. Optional transmissions included an automatic or a four-speed manual (Four on the floor became an option starting during the 1961 model year).

Though I don’t have hard data, based on a casual observation, I suspect that the majority of the Corvair cars were purchased with an automatic, though the four-speed manual is more highly sought after today.

The Corvair’s automatic transmission was a specially designed variant of the “Powerglide” transmission offered in other Chevy cars and trucks of the time. It was a tw0-speed automatic with low gear having a 1.82:1 ratio and high 1:1.

With today’s cars featuring automatics of 6 speeds (or occasionally even more!) the idea of a two-speed automatic seems quaint, yet the performance of the Powerglide wasn’t all as bad as people might assume. The theory behind the two-speed automatic was that you had two mechanical gears provided by the planetary gears and clutches of the transmission and you had a theoretically infinite number of gears provided by the torque converter. The maximum gear reduction on the torque converter is 2.6:1 which would be multiplied by the mechanical gear reduction. For example, in low gear with the torque converter at maximum load would be 2.6X1.82 or about 4.7:1. Zero-to-sixty times for Powerglide equipped Corvairs was actually slightly faster than that of three-speed manual cars, though not as fast as equivalent cars with a four speed stick. Corvairs compete very well in autocross racing due to the superior handling abilities of the car (contrary to popular belief) and Powerglides are preferred by many drivers for autocrossing because of their responsiveness in the speed range typically driven in autocrossing (and with only two mechanical gears, the transmission doesn’t waste a lot of time going between gears). Drivers would typically drive with one foot on the brake and one on the gas.

The Corvair Powerglide transmission has a reputation of being extremely rugged and reliable to the point of being virtually bulletproof and there are quite a lot of them in regular use today that have never been taken apart.  It was a design requirement that the Powerglide had to be able to withstand 100 Low-to-Reverse shifts at wide open throttle on dry pavement as this was considered normal (!) usage. This leads to a bit of a conundrum I have with mine.

On the one hand, I am doing a ground-up restoration of the car, and the transaxle (transmission and differential assembly) is out of the car (and sitting on my workbench at the moment as one can see in the photo above). It might seem prudent to take the thing apart, clean out everything inside, replace all the gaskets, seals and clutches etc and put it back together). However, a great many Corvair experts are of the “if it ain’t broke, don’t fix it” mindset especially when it comes to Powerglide transmissions. At the very least, I will take off the pan on the bottom and see what has settled to the pan to see if there are any metal parts or shrapnel¬† sitting in there. The automatic transmission fluid that has leaked out through the shifter cable hole so far has looked pristine as if it were poured in to the transmission yesterday. I’m not sure really whether I plan to take it apart or not, but will at least wait until I see whether there’s anything distressing in the oil pan.

One Corvair veteran advocates strongly for rebuilding the differential due to the propensity of inner pinion seals to fail. I will look into this. At the least, one can see that I have begun to clean off the outside of the assembly. The transmission is encased in an aluminum case, hence the nice shiny silver appearance to the parts of it. The differential is in a cast iron housing and hence the surface rust over the whole thing.

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3 Responses to The Corvair Powerglide transmission

  1. corvairdad says:

    I wouldn’t hesitate – do the rebuild. I just finished doing one using Clark’s kit C185A (soft parts only). This was a low-mileage PG that had sat for about 35 years, so the seals were like cardboard. The only special tools required were an arbor press (I used my drill press) and snap ring pliers (cheapo kit from Harbor Freight).

  2. I am definitely leaning toward doing it. And you are the expert these days, no? :)

  3. Anja66vair says:

    Hi I have a question I have a 66 Corvair Monza 110HP and my tranny leaks when it sits. I heard something about a valve in there that gets stuck either open or closed and it make this happen??!! any advise on how to fix the problem?

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