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, disc wheel / outboard drum brake 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 documet 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 Maintenance Council (TMC) Recommended Practice #RP-618.

Rationale

—This document has been reaffirmed to comply with the SAE 5-Year Review policy.