Torque converter lock up?

[F14CRAZY]

What does it mean? I've heard it said a few times like "the torque converter locks up at 2800 RPMs" Please explain. Thanks (for letting me ask something so dumb...)

 

[MrShorty]

One of the traditional complaints against automatic transmissions is they get worse gas mileage. This is because the engine and transmission are "coupled" through the ATF (a liquid or "fluidic" coupling) as opposed to the mechanical connection that a clutch plate offers. To get automatic transmissions to get better gas mileage, someone came up with the idea of putting a "clutch" inside the torque converter to provide the same kind of mechanical connection between the engine and transmission. Check out the article on torque converters at www.howstuffworks.com

 

[Opera House]

Just to add

The TC doesn't lock up at any particular rpm. Pressing the brake unlocks the converter. The TC will lock up only in the higher gears and when the the engine is lightly loaded. The TC not only provides a fluid slip but can multiply the torque of the engine. This is why the TC doesn't lock in lower gears and often unlocks when accelerating to pass.