Field and Laboratory Evaluations of Automatic Transmission Fluids

An outline of the field testing of automatic transmission fluids in two New York City taxicab fleets over a three-year period is presented. The field testing of six fluids in each fleet was found to be a suitable method for evaluating their relative quality. Some fluids performed satisfactorily for 11,000 miles while others were in service for over 90,000 miles. With extended fluid drain intervals, the major cause of transmission malfunction was fluid oxidation. No significant relationship was found between the field test results and motor driven transmission and beaker bench oxidation tests. A fairly good correlation was established with engine driven cyclic transmission tests. The theory and modes of transmission malfunction are also discussed.