It’s a System
The correct ATF is important

By Robert King
Senior Research Engineer
University of Dayton Research Institute

Torque converter clutches (TCC) have been around since the mid to late seventies. The primary purpose of the TCC is to assist with improving fuel economy by providing a mechanical lockup to the transmission. The secondary function is to provide torsional damping to the driveline. The original design only required the TCC to be either fully applied or released using inputs from the throttle position switch, speed of the vehicle and manifold absolute pressure sensor. Engagement only occurred above approximately 35 MPH while the vehicle was cruising in the final drive gear.

Over the past several years automotive manufacturers have increased the breadth of the engagement cycle using calibrated computer controls. This allows the TCC to be partially applied (slipping) at lower speeds and in different gears along with full lockup at cruising speeds which accounts for additional fuel economy. The newer computer controlled TCC systems present some formidable problems for the design engineers and system calibrators. New friction materials containing carbon particles or carbon weave were developed to provide the required performance and durability to survive in the elevated temperature environments. The computer controlled TCC requires automatic transmission fluids with special modifier packages to enhance the durability and performance of the latest generation friction materials.

Manufacturers have developed their own TCC systems which includes (in most cases) automatic transmission fluid specifically developed for their applications. Substituting alternate fluids for the recommended fluid may cause performance problems (chatter, reduced friction material torque capacity) and/or durability problems (reduced friction material life due to heat glazing and/or accelerated wear). The new systems are so smooth when working properly, their application is transparent to the driver. The owner of the vehicle may not be happy if after having his converter replaced he starts noticing the torque converter clutch engagements. Remember, the toque converter clutch is part of a system comprising of the friction material, automatic transmission fluid, and calibrated computer controls. Using the correct automatic transmission fluid may alleviate unnecessary converter replacements and unhappy customers.