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Developments in axle nut configurations now make it possible to position wheel assemblies on the axle spindles of heavy duty combination tractor/trailer vehicles using new installation procedures to assure ideal adjustment of the tapered roller bearings. The ability of all mechanics to accurately control the assembly of wheel end components will be enhanced with axle nut designs conceived in the last two years. Of great significance in this area of interest are pronouncements by tapered roller bearing engineers who now advocate that longer life will be realized for all wheel end components if a limited amount of tapered roller bearing “preload” is introduced and maintained with a mean of finite axle nut adjustment. Until recently, there appeared to be reluctance on the part of the tapered roller bearing manufacturers to advocate improvement of tapered roller bearing service life with application of preload pressure.

The purpose of this paper is to examine the factors which initiate, contribute to, and subsequently cause the occasional loss of tractor or trailer wheels while under way on the nation's highways. Specifically, these are wheel loss failures which are characterized by deterioration of the axle nut system. Of major significance is the explanation of how the axle nut will degenerate to the extent the wheel can no longer be retained on the axle spindle. There are a number of reasons which cause the separation of either the hub or the wheel from the axle spindle. Initially, the various types of axle nut systems will be categorized and identified by type. The variations and their potential for wheel separation failure are discussed and evaluated. Of interest for examination are the following axle nut systems: 1. The Single Castellated Axle Nut With Its Means Of Securement Provided By A Cotter Pin. 2. The Conventional Double Jam Nut System. 3.