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Over the past several years, economic pressures have driven fleets to substantially increase their maintenance intervals. To meet this challenge, both the Original Equipment Manufacturers (OEMs) and the lubricant suppliers have developed new and better products to give fleet users the benefits of extended service intervals, while at the same time maintaining equipment life and providing the potential for reduced operating costs. Through the selection of proper lubricants, fleets can now minimize their total operating costs with products that meet the OEM extended service specifications, have demonstrated equipment durability, and are formulated using base oil and additive components to minimize the cost of the lubricant. This paper will examine the options available for formulating extended drain transmission and axle lubricants. It will explore the selection of the lubricant base oil as well as the additive system.

Heavy-duty axle and manual transmission lubricants formulated with Group II base oil and borate additive chemistry were tested in a 250,000-mile, extended-drain, on-highway field test. For reference, units using a synthetic sulfur-phosphorus axle lubricant and a synthetic engine oil type transmission fluid were monitored. The field test involved two major fleets with approximately 200 trucks. Twenty axles and transmissions using the Group II borate chemistry lubricants were inspected as they reached greater than 275,000 miles. Oil analysis was performed on the units running on the test and reference lubricants. Test data indicated that all four lubricants performed well. However, end-of-test oil analysis data showed significantly less wear with the Group II products formulated with borate chemistry compared to the reference products. In the axle test, the iron wear rate for the Group II borate chemistry lubricant was 56% lower than the iron wear rate for the synthetic axle lubricant.