Description / Abstract:
This SAE Recommended Practice applies to the four primary, large
volume applications in the class 7-8 heavy-duty market place, as
specified in SAE J1842:
a. "N" trailer axle
b. "R" powered rear axle
c. "FF / FG" nonpowered front axle
d. "P" trailer axle
This document applies to on-highway applications. It is not
applicable to those applications that exceed the GAWR ratings or
the load line restrictions listed in columns "A," "B," and "C" of
Table 1. Load lines are measured from the inboard bearing cup
backface as shown in 3.4.
This document establishes preload force values only. The
methodology to obtain these force values must be determined by the
fastener supplier and/or axle assembler.
This document reviews the bearing system. It is NOT intended to
prescribe (new or existing) axle and/or hub manufacturers' ratings
and/or specifications.
Purpose
The purpose of this document is to list acceptable axial bearing
preload force values for conventional wheel-end components used in
heavy-duty tractors and trailers.
The audience of this document is intended to be the axle and/or
component engineers. The user should be aware of both the benefits
and the risks of this practice.
a. Benefits - Bearing and seal life can be maximized when the
bearings are adjusted to a light, controlled preload setting.
b. Risks - The benefits of a light and controlled preload
bearing setting are negated if bearing preload force is excessive.
Care must be taken to ensure that preload force does not exceed the
recommended amounts. Excessive preload can cause high operating
temperatures, reduced lubricant life, reduced seal life, and
premature bearing damage. Bearing lock-up and/or wheel-end assembly
separation may occur if the preload force is excessive. A light
preload bearing setting should only be attempted if the entire
bearing setting process is accurate and repeatable.
For adjustment recommendations where bearing end-play is
desired, refer to The Technology and Maintenance Council (TMC)
Recommended Practice #RP-618.