Development of a Sprag Wear Test Procedure for Evaluating the Antiwear Performance of ATF's

A sprag clutch wear test procedure for evaluating the antiwear performance of automatic transmission fluids (ATF's) has been developed using a bench test apparatus. The wear test procedure provides an effective screening tool for incorporation into Automatic Transmission Service Fluid Qualification Test Procedures and Specifications. Two, widely-used ATF's provided reference data for wear comparisons and seven ATF candidates were evaluated for their antiwear performance. In addition, an additive-free, mineral-oil base stock was tested to highlight the need for fully-formulated fluids in automatic transmissions. Surface texture analysis complemented the weight-change data which was used as the primary wear criterion. Supplemental tests which examined sprag components at various intervals throughout the test period provided sufficient data to suggest a possible mechanism for wear initiation and propagation in the sprag clutch.