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High lubricant temperatures generated during the break-in of new differential assemblies has been of concern among original equipment manufacturers (OEM's). Many tests have been devised to measure the effects of speed, load and lubricant on the temperature generated in the axle. The major problem confronting the use of these tests has been a lack of repeatability and/or reproducibility. Recently, a European OEM axle lubricant break-in test procedure using a European sedan test vehicle has demonstrated highly repeatable and reproducible results. Test work had been limited to the European sedan. The applicability of the European OEM test procedure to a larger domestic U.S. vehicle was questioned. This paper discusses the applicability of the European test to a domestic sedan. Additionally, two other axle break-in test procedures were conducted using the same domestic sedan test vehicle. Three sulfur-phosphorus multi-purpose gear lubricants were evaluated.

It has been recognized for many years that multipurpose axle lubricants give rise to much higher axle break-in temperatures than lead-soap, active-sulfur or sulfur-chlorine-lead lubricants. Evaluation of differences in axle lubricant break-in temperature between the various multipurpose gear lubricants has been complicated by lack of repeatability and reproducibility. The work described in this paper shows that one of the most important variables affecting axle break-in temperature, under the conditions of the test technique used, was torsional axle preload and that control of dimensional preload in itself is not sufficient to ensure good test repeatability. The test technique described here has been used to evaluate the axle lubricant break-in temperature properties of several sulfur-phosphorus multipurpose gear lubricants.