1973 Citroen SM from North America - Comments

28th Mar 2004, 22:32

An automatic transmission actually multiplies torque, so you get more power than a manual. Just a FYI, but a manual is more fun.

5th Apr 2007, 11:12

Re. Torque converters: Any gearbox is exactly that, a torque converter. When you're in a low gear, the wheels move a lot more slowly, but with a lot more torque. The extra torque comes from the reactions within the gearbox (manual) or torque converter (auto), and MUST be accompanied by a decrease in wheel speed: thus, the POWER (= torque times rpm) is constant. All of the power comes from the engine: a torque converter can't give you any more power!

In fact, a torque converter usually works on fluid flows within, which have friction losses that you don't get with a conventional gearbox. That's why an automatic sucks power out.

12th Feb 2011, 08:36

On "torque converters": Older automatics' fluid couplings/torque converters "slipped" all the time. the slower the rotation and the higher the torque, the more slippage. More recent TCs often have locking mechanical friction clutches in them that, when engaged, lock the input (coupling/converter case, which is fastened to the engine crankshaft, to the output (gearbox mainshaft), eliminating this slippage and power loss. During acceleration, and in the lower ratios of the gearbox, the TC slips and multiplies torque. Heating of the fluid is rapid. As soon as cruising speed is attained in high gear, the mechanical clutch locks up, bypassing the fluid coupling. The mechanical clutch works much like the dry clutch of a manual shift, but as it is inside the TC, it is "wet": immersed in fluid.

An early (1949) locking ("Direct Drive") automatic was the Packard Ultramatic, also marketed as the (1954) Gear-Start and (1955) Twin Ultramatic. It is (now) an excellent machine. Modern materials and manufacture of rebuild parts, and the efforts of enthusiasts, have overcome the deficiencies of the original transmissions. Packard introduced (1956) aluminum in the transmission case, which led to other makers following.

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