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In a Guest Editorial published in the January-February, 2010 issue of Fleet Maintenance Magazine, several problems associated with maintenance of trailer wheel-end systems were discussed and predictions were advanced that newly developed concepts would provide improved wheel-end component design. 
Lately, in reflecting on one prediction suggesting that component suppliers will provide improved maintenance instructions, it is possible that I was overly optimistic.  It appears there is little motivation for the suppliers of wheel-end components to offer alternative recommendations relating to the installation of preload adjustment of wheel bearing adjustment other than what has been offered in the past fifteen years.
The purpose of this follow-up advisory is to provide the means to encourage wheel-end component manufacturers to initiate development activities for advancements that would be of benefit when applied to fleet maintenance operations.

The following graph provides information that has not been previously provided by any manufacturer within the trailer industry.  Apparently this is the case because members of the transportation manufacturing community have been unwilling to publish suggestions on how preload can be controllably installed.

All mechanics are aware that drag (resistance to the ease of wheel rotation) increases as the spindle nut is tightened.  However, it has never been disclosed that drag increases proportionately with the amount of additional preload.  This information is important because drag can be associated with the temperature of the tapered roller bearings while in operation.  If, for some reason, the adjustment nut was tightened with excessive preload, the operating temperature of the wheel assembly may reach critical levels and could contribute to tapered roller bearing destruction with the consequence of wheel separation from the vehicle.

Excessive drag can be dangerous, but an ideal level of drag will occur if the preload adjustment of the tapered roller bearings is kept to a minimum.  It would be sensible to make sure the procedures you use for the installation of the wheel-end assembly provide the least amount of controlled preload as possible.

Copyright © 2010 by G. Allan Hagelthorn, P.E.
This manual may be reproduced or transmitted by non commercial entities for educational purposes.  All other rights reserved.