<VV>Economy in 1959 now Dynaflow-no Corvair

[Frank DuVal]

Padgett wrote:

>
> Jetaway and Dynaflow were also two speeds (though Buick had a "switch 
> pitch" torque converter that made it feel like a three speed - 
> forrunner of the lock-up torque converter.
>

Well, partially right. The Dynaflow could be considered a two speed as 
it has a planitary gear set and a L on the shift quadrant. But, low must 
me manually selected. When in Drive, there is no changing gears, just 
1:1 ratio as far as the gears are concerned. All the torque 
multiplication is with the torque converter. Now, I am speaking of the 
1956 model, as I am most familiar with this one. Earlier models had 
simpler torque converters, but still no shift in Drive, just less 
mutiplication. I have read that the first Powerglides also did not start 
in low gear, but just let the torque converter provide dismal 
acceleration at 1:1 ratio.

The torque converter has 5 segments. One of these is the switch pitch 
feature, where by holding one of the segments with a clutch there is 
another range of torque multiplication. This pitch is not variable in 
1956, but switches mode with the accelerator pedal like a kickdown 
switch on a Turbohydromatic 400. So in Drive you can floor it and get 
maximum torque multiplication from the converter and 1:1 through the 
tranny gear set for "decent" off the line acceleration and passing gear 
operation at speed.

Now, you may manually select Low and floor it and get maximum torque 
multiplication times whatever the low planetary ratio is. Now, that is 
much better off the line performance.

But, remember the switch pitch is activated by the acceleraotr pedal. To 
really impress your friends, start in Reverse from standstill and floor 
it. Maximum torque conversion times low gear ratio times reverse ratio. 
Let off the accelerator and the pitch changes, your friends will think 
it just upshifted in reverse!

 Not many other trannies had a passing gear in reverse!

So, anybody else work on a 4 cylinder Chevy II with Hy-Drive? A manually 
shifted Powerglide!

Frank DuVal