Higher horsepower and increased low-gear ratio in automatic transmissions have resulted in several-fold increases in axle gear loading in both passenger cars and commercial vehicles. Lubricants and lubrication have become a limiting factor in axle performance, and single-purpose factory fill lubricants and the older multipurpose lubricants have not kept pace with the new requirements. Extensive research by lubricant and additive manufacturers has resulted in a new type of multipurpose gear lubricant possessing the anti-scoring advantages of active-sulphur-type lubricants and the desirable anti-wear and low friction characteristics of more inactive type products. The performance of the new type gear lubricants has been proven in extensive tests in different types of vehicles under a variety of severe operating conditions. New axle test methods have been developed for incorporation in an upgraded version of Specification MIL-L-2105. The development of a Reference Gear Lubricant Scale accompanying this work has facilitated evaluation of axle requirement levels and lubricant quality levels. The new-type products have been designated by Industry as “Multipurpose-Type Gear Lubricant for API Service GL-4” The advantages of the new products to civilian users and the Military are covered. Continuing problems arising principally from the trend to higher temperatures and the need for continuing cooperative effort are described.
