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This paper reviews the development of automatic and powershift transmissions for both on-highway and off-highway trucks. Firstly, it discusses the development of the current generation of powershift transmissions and some of the technological factors that have influenced them before going on to look at some of the alternative types of automatic transmissions that have either been considered in the past or that are being considered for the future.

Market studies show there is a strong need for an automatic transmission for trucks in the 10,000 to 27,500-lb GVW class. After the area of the truck market is defined, the design of a new automatic transmission - the Allison AT-540 - is presented. The transmission's function, arrangement, and features are described. Also, the development program implemented to qualify the transmission for the market is discussed. Of significant interest is the durability test program, wherein a maximum of experience is obtained during this period of development. The data accumulated during the development test program indicate the objectives stressed during the design of the transmission - durability, performance, and cost - were fulfilled.

Original paper friction materials were energy limited and their use confined to light duty vehicles. Recent innovations in paper friction material compositions now permit consideration of this type of friction facing for all wet friction applications. A comparison of the properties of these new materials with those of traditional paper friction compositions, demonstrates the attractive features of the new materials. New friction paper compositions allow the potential user to select desired properties from a wide range of performance characteristics. The installation of an automated paper friction clutch disc production line further enhances the reliability and cost-effectiveness of paper friction materials.