Quote:
Originally Posted by vic guilmino
Did anybody make a conv. for the 58 hydro
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Vic,
The '58 transmission (called "Jetaway" by Olds and "Strato-Flight" by Pontiac, was an outgrowth of the transmission that everybody used in the sedan deliveries, but with some basic differences. No parts would interchange between the two, that I am aware of.
First off, neither transmission used a torque converter, per se. They both used fluid couplings, which are nothing but a torque converter without a stator.
Fluid couplings allow slippage so that the engine can run at an idle without moving the car when it's "in gear."
Torque converters do that PLUS they have the capability of multiplying input-shaft torque like a conventional gearset. They get this additional capability through the use of a "stator", a set of rotating fins which redirects fluid so that it hits the driving turbine at an angle. As I try to explain how this works, I realize that I am in no way qualified to try to illustrate how this accomplishes torque multiplication..
Trust me; it does.
Lacking this torque-multiplying capability, the hydros (both of them) had, of necessity, first gear ratios in the high 3's, or low 4's. A TH350/400 could get by with something like a 2.45:1 ffirst geat because they had the torque multiplication from the converter to help get the car rolling.
It was possible to modify the fluid couplings in the hydramatic transmissions to increase stall speed by reducing the amount of vane area exposed to fluid, but there was no change in gearing like you get with a high-stall onverter.
Generally speaking, I believe that as stall speed increases, so does the amount of torque multiplication; not so with the fluid couplings. It's still 1:1.
If I'm wrong about that converter/stall business, somebody please correct me.
At any rate, the '58-up hydros were thought to be somewhat less efficient than the earlier units, but still could be a workable racing transmission. Lots of Pontiacs, in particular, ran really fast times with those dual-coupling hydros.
I don't think that stall speed was a problem.