Quote Originally Posted by deermagnet View Post
Well, no. The torque converter clutch is part of your automatic transmission. As you shift thru the gears it's a 100% fluid connection between the flywheel and the rear drive shaft, and with that comes horsepower loses.
That viscous coupling is commonly referred to as the torque converter. It used to be a big thing to upgrade your torque converter to a lower stall speed unit to cut down on the HP loss that he mentioned (at the expense of it shifting harder). Also, if you ever buy a tow vehicle with a factory tow package installed, that's one of the upgrades.

Picture this: next time you are stirring your coffee, stir real hard & then let go of the spoon. It'll keep spinning after you let go as the liquid pushes the spoon in the direction of the flow.

The torque converter is very much like a vat of hydraulic fluid with 2 concentric fans. The primary fan is connected to the engine. The secondary is connected to the output shaft of the tranny. As the engine turns the primary fan & spins the fluid, the fluid drives the secondary which turns the driveshaft.

This is all necessary for an automatic transmission to function properly.

Lock up torque converters are probably the biggest contributor in getting auto tranny vehicles to get comparable gas mileage to what manual trannys get.