We are aware of Company's that are recommending people use non-locking (dummy) style torque converters. This just doesn't make any sense to us for the following reasons:

First: When a modern torque converter is in its engaged (locked up) or mechanically coupled state, it creates a direct mechanical connection between the engine and the input shaft of the transmission! The connection thats created during lock up is almost identical to the mechanical connection that occurs whenever the driver lets out the clutch pedal in a standard transmission vehicle and creates a very efficient means of transmitting torque from the engine to the transmission! The U.S. government has stated in many reports that this feature has been responsible for a major improvement in fuel economy. This has been well documented and really isn't debatable.

Second: When the converter is in an unlocked (disengaged) state, there is going to be some loss (slip) across the converter during almost all driving situations because of converter slip. The results of this loss or slip is work heat generated into the transmission fluid. How much heat depends on how much loss (slip) is occurring during a specific driving situation. Some of the factors that effect the amount of heat generated, include towing, driving speed, climbing steep mountains or hills, wind effect and weight being carried etc. Overheating is the number on cause of failure in automatic transmissions so controlling this heat is very critical to longevity. As long as the cooling lines are routed to the vehicles radiator, no heat generated inside the torque converter while driving is always better than some heat! Dummy or non locking converters never lock up and are therefore a constant source of heat than must be effectively dealt with.

Third: Lowering the engine RPM while driving at highway speeds is the very goal of overdrive gearing but this can easily drop the engine RPM below the effective "coupling" speed of the torque converter. This can cause tremendous heat generation inside the torque converter and must be controlled. Engaging the torque converter clutch eliminates all heat production.

Fourth: Just like pedeling a ten speed bike, this higher the gear ratio your in, the greater the torque that must be supplied to maintain a result. Transmissions by the very design are meant as multipliers of engine torque, for example, while in 3.06:1 low gear, 100 lbs/feet of torque applied to the input shaft will result in 306 lbs/feet leaving the output shaft! Second gear, the same 100 lbs/feet of torque applied, results in only 163 lbs/feet of torque at the output shaft. Third is 1:1 so the same 100 lbs/feet of torque leaves at 100 lbs out! Overdrive gearing results in a torque loss across the transmission since 100 lbs/feet in results in only 70 lbs/feet out! This means to achieve the same results while in overdrive, the engine must supply 30% more torque to the input shaft! This results in working the fluid inside the torque converter 30% harder any time the transmission is in overdrive! The result of the added work is heat. High stall converters make this phenomonom even more severe. Locking (engaging) the converter clutch eliminates this problem!

Fifth: Having the ability to "engage" the torque converter clutch in other ratios like second or third gear, gives the operator the opportunity to stop overheating the transmission fluid by the simple use of an electrical switch. Cooling systems cannot stop overheating of the transmission from occuring. The best a cooling system can do is eliminate the excess heat and bring the transmission fluid temperature back to a normal state. The finest cooling system cannot stop fluid degradation since this will occur inside the torque converter before it even goes to the cooling system. Burnt fluid can certainly be brought back to a normal operating temperature but is will still be burnt up! Locking the torque converter stops the production source!

ADDITIONAL OBSERVATIONS AND RECOMMENDATIONS

If you are going to use a high stall converter, tow, haul heavy loads, have a lifted vehicle with big tires, etc, we strongly recommend installing a temperature gauge to monitor the fluid temperature inside the transmissions pan. The fluid in the pan is primarily fluid that has just returned to the transmission after passing through the heat exchanger located inside the vehicles radiator. Locating the temperature gauge sender in the transmissions pan will tell you whether your vehicles temperature control system can handle the temperature management properly. We have installed and monitored all vehicles that have been through our shop over the last eight years and consistantly see 140 to 160 degree F in the pan when the factory cooling system is working correctly. As an observation; the temperature between what you see on the engines temperature gauge and the fluid temperature inside the transmissions pan should always maintain a 30 to 50 degree F spread! Always!

Remember, the temperature you observe on the gauge is telling you the fluid temperature after it's been cycled through the radiator heat exchanger! This reading has nothing to do with how hot the fluid got inside the torque converter. If it reached 300 degrees F inside the torque converter and you only see 150 degrees F at the sensor in the pan, it doesn't mean the fluid wasn't overheated and degraded! We do not know of a reasonable way to monitor the fluid temperature inside the converter, so we always assume it is very high during hard work situations. Locking the converter during high heat production situations is the only way to prevent the overheating from occuring in the first place!

The manufacturers of Dextron III transmission fluid have told us that a continuous steady 150 to 160 degrees will yield maximum longevity for the fluid. This is not possible because of the various driving situations you subject the fluid to so proper management of the torque converer clutch is the only reasonable way we have found to eliminate fluid degradation from overheating. I'm sure most of you have seen the charts that show the rapid destruction of transmission fluid properties as operating temperature increases. Most charts show a 50% loss of fluid life for every 15 degrees of operating temperature increase above their designed ideal operating temperature, normally 165 degrees F. This is the reason we recommend each fluid cycle start at 150 degree F. or less.

We also recommend a complete annual flush of the transmission fluid. We have a very simple method we teach our customers so they can change the whole systems volume not just the 4 1/2 to 5 quarts you can change by draining the pan.