Preload Adjustments of Wheel Bearings on Tractor-Trailer Combinations - The Factors of Compliance 2004-01-2693

This technical paper continues a sequence of previous SAE Technical Papers that document progress of wheel bearing adjustment on tractor/trailer combination vehicles. In an earlier SAE paper, 2000-01-3496, misinformation provided was recognized. This material is reviewed following the conclusion of this technical paper and corrections are offered. However, of primary importance, disclosure will be made of new developments accomplished in wheel bearing preload adjustment procedures since December 2000. The intent of this paper is to advise the means by which selected amounts of preload can be introduced into trailer wheel assemblies. These are identified as axle nut adjustable systems that are serviceable by mechanics in commercial carrier fleet operations. No commentary will be presented relative to the permanent type of wheel bearing adjustment systems that are factory installed and are unable to be adjusted while in service.

Since SAE Technical Paper, 2000-01-3496 was presented, the SAE Standard, J2535, Setting Preload in Heavy-Duty Wheel Bearings was issued. SAE member engineers associated with the tapered roller bearing manufacturing industry produced this document. Following J2535, the recommended practice RP-640 was published by the Technology and Maintenance Council of the American Trucking Associations (TMC) acknowledging the allowable range of preload presented in the SAE document. It is now possible for a mechanic to use the information provided by the SAE and the TMC to install acceptable and desirable preload within trailer axle assemblies using an adjustable type of nut system as long as the results are manageable. It has been a firm requirement by all tapered roller bearing manufacturers that the installed range of preload be controlled at the time the wheel components are installed. Because of this, both the SAE and the TMC require that those who install wheel end fasteners follow specific instructions provided by the spindle nut manufacturers. That being said, this technical paper will describe a new method to achieve accurate preload adjustment.