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This paper discusses four methods for measuring the resistance of transmission fluids to permanent viscosity loss through shear. The four methods include the Fuel Injector Shear Stability test, the Sonic shear test, the DEXRON®-III Cycling test and the KRL test. Each of these methods and their advantages are discussed and data provided for many OEM fluids and the effects of these methods on the final viscosity. The data indicates the KRL generates the maximum shear stress on the fluids compared to the other methods. The data also indicates the sonic shear method results are similar to those of the KRL test. The fuel injector test imparts the least stress to the fluid. Data is presented to show the correlation between viscosity changes obtained using these methods and viscosity changes observed with mileage accumulation in vehicle transmissions.

The friction characteristics of several DEXRON®-III automatic transmission fluids were examined in a variety of friction tests. These evaluations included tests with SAE No. 2 Friction Machines using either Band or Plate heads, breakaway friction tests, and low-sliding speed friction tests. The effect of bulk fluid temperature on friction performance was examined in band tests and in breakaway tests using the plate clutch apparatus. The DEXRON®-III fluids were compared to the previous generation automatic transmission fluids. Results showed that the DEXRON®-III fluids exhibited more desirable friction characteristics; for example, with the DEXRON®-III fluids in the band machine, dynamic friction remained stable during sustained operation at high temperature, whereas with DEXRON®-IIE fluids, dynamic friction decreased as much as 25%.

In recent years, the slip lock-up mechanism has been adopted widely, because of its fuel efficiency and its ability to improve NVH. This necessitates that the automatic transmission fluid (ATF) used in automatic transmissions with slip lock-up clutches requires anti-shudder performance characteristics. The test methods used to evaluate the anti-shudder performance of an ATF can be classified roughly into two types. One is specified to measure whether a μ-V slope of the ATF is positive or negative, the other is the evaluation of the shudder occurrence in the practical vehicle. The former are μ-V property tests from MERCON® V, ATF+4®, and JASO M349-98, the latter is the vehicle test from DEXRON®-III. Additionally, in the evaluation of the μ-V property, there are two tests using the modified SAE No.2 friction machine and the modified low velocity friction apparatus (LVFA).