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A GL-5 gear lubricant containing a dispersed solid borate additive and a CD synthetic engine lubricant were evaluated in the overdrive transmissions of 17 new Class 8 trucks in a 500,000-mile per truck, on-highway field test. With 500,000-mile oil drain intervals, both lubricants gave acceptable performance as judged by end-of-test inspections: deposit/sludge formation was minimal, overall wear was low, and seal/yoke performance was good. The borate lubricant gave a statistically significant lower wear rate than the synthetic lubricant based upon oil sample analysis; inspections also showed lower wear on some parts. Additionally, oil sample analysis from the tandem drive axles showed that the forward axle gave a statistically significant higher wear rate than the rear axle. Transmission and drive axle oil temperatures were monitored during a portion of the test.

Four GL-5 gear lubricants, one containing a dispersed solid borate additive, two sulfur-phosphorus (S-P), and a S-P synthetic, were evaluated in the axles and transmissions of 26 new Class 8 trucks in a 250,000-mile field test. Significantly lower axle break-in wear (factory to first oil change) was found for the borate lubricant versus a S-P factory-fill oil. The four test oils showed statistically significant differences in axle wear as shown by iron wear plots and analysis of end-of-test parts: the borate and synthetic oils were equal while the other two oils gave higher wear. All oils gave acceptable seal performance. The borate lubricant showed the best thermal stability as judged by parts cleanliness.

A new “beyond GL-5” gear lubricant technology has been developed which combines soluble additives with a dispersed borate solid lubricant. The L-37 and L-42 axle tests as well as laboratory bench tests show a strong synergistic effect between the solid lubricant and the soluble additives. The new technology shows improvements over conventional chemistry in antiwear performance, seal compatibility, and oxidative/ thermal stability. These improvements were demonstrated in over 17 million field test miles in axles and transmissions of Class 8 trucks.