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What is a Torque Converter and what does Lock-Up mean?

April 29th, 2009

A torque converter, common to automatic transmissions only, is the equivalent to a clutch in a standard transmission. The torque converter converts the power from the engine, seamlessly and smoothly to the transmission instead of having a clutch to assist on take off as in a standard transmission.

BTW, if you don’t get a remanufactured torque converter with a remanufactured transmission, I would question the job and feel like the job was not complete. You don’t have to guess with a supplier of transmissions like GotTransmissions.com

Nowadays all cars and trucks use a feature called lock-up in the torque converter.

By way of fluid coupling, the torque converter transfers the power to the transmission without a clutch or clutch pedal. It cushions the shifts as they occur and makes the transition of power very smooth as the automatic transmission shifts.

What I wanted to discuss was not the technical details of how the actual parts work in a torque converter, heck most transmission mechanics don’t understand the theory behind it. Something else to throw out quickly is that very few transmission rebuild and repair shops rebuild their own torque converters. The amount of expensive equipment and the knowledge necessary to perform this is better off done by a torque converter remanufacturing specialist.

I wanted to briefly mention what the term lock-up means. Lock up is a feature introduced in about 1982 with the advent of the T-700R4 and T-200-C General motors transmissions. Simply put, since a torque converter is a fluid coupler it will always have a certain amount of ‘slip’ built into it. It is unavoidable due to fluid being the main component of the coupling action. This decreases gas mileage by 1-4 miles per gallon, the built in slippage, that is.

To eliminate the problem, an actual clutch disc has been built right into the torque converter. At a certain speed, usually about 45-50 mph a message from a computer sends a forceful ‘charge‘ of automatic transmission fluid to the converter, which applies the clutch plate inside and eliminates the small amount of built in ‘slippage’.

Darn good idea. A lot of updates and improvements have been developed over the years which has just about perfected the design. Obviously this is a desire-able feature with few drawbacks. The only legitimate drawback is if your son takes the car to the drag-strip and burns the converter clutch up.
Just joking, the drawback, which is negligible, is it produces more heat, therefore making maintenance using synthetic ATF more important and the installation of an external transmission cooler a good idea.

Once I link this post to some of the more technical posts on GotTransmissions.com Blog, those posts will make more sense. Assuming any of my posts make sense. Let me know if you need more information or a better description. If you don’t tell me I can’t do a better job. Thanks and enjoy.

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