Qualitative discrimination between API GL performance levels of manual transmission fluids by comparing their EP properties determined in a new four-ball scuffing test

To prove that a candidate MTF meets the requirements of a given API performance level, one needs to perform extremely expensive and time-consuming tribological tests on entire lorry units. quick and inexpensive four-ball test method, performed under scuffing conditions was used for testing EP properties of MTFs of GL-1 to GL-5(LS) performance levels. The test makes it possible to discriminate between API performance levels in a “qualitative” way—by the friction torque analysis. For interpretation of the results, scuffing models in different phases were developed on the basis of tribological tests and surface microanalyses.