Anti‐shudder durability of automatic transmission fluids: Mechanism of the loss of shudder control

Field samples of automatic transmission fluid (ATF) from vehicles fitted with controlled-slip torque converter clutches have been analysed to determine the cause of the onset of vehicle shudder. A laboratory anti-shudder test has been developed using the SAE No. 2 machine. This test includes several degradation mechanisms: thermal degradation in engaging clutches, oxidative degradation in the presence of catalytic metals, and degradation produced by a continuously sliding clutch. At least in the case of one specific fluid, the mode of failure produced in the laboratory test was very similar to the mode of failure in the vehicle. Fluids with improved anti-shudder durability have been evaluated by this test method and fail by different mechanisms. Test matrices have been conducted to separate the contribution of fluid and hardware to the loss of shudder control in these systems.