Bearing failure occurs due to excessive heat
Related to the previous story, we thought it was important to find out important factors of heat related failures.
As far as lubrication goes, transmission fluids lose their ability to lubricate bearings and thrust surfaces when the temperature reaches the 240 plus range. Some premium ATF can protect as high as 425 degrees before oil degradation begins. Bearing life is cut in half for every forty degrees increase after hitting the 240 degree marker. If a thrust bearing that is designed for a maximum 400 PSI is increased beyond fifteen percent, the likelihood of failure occurring is increased by fifty percent. It is important to replace any available torque converter bearings at the time of rebuild to insure the highest possible standards.
The verdict is still out on whether or not all bearings need to be replaced at the time of rebuild. More and more rebuilders find the cost of the bearings does not outweigh the quality assurance.
Transmission fluid additives that contain extreme pressure lubricants, friction modifiers, antioxidants and viscosity stabilizers such as LubeGuard or Midco’s TOS (Transmission Oil Supplement), will extend the transmission fluid’s ability to reduce friction and heat. Other additives are available, and you can check the labels to see if they contain extreme pressure lubricants and friction modifiers. Be careful here: As a rule of thumb, if one bottle is good, two does not necessarily make it better. Avoid over treating the ATF beyond manufacturer limits.
Found in issue 07, 2004