Is there a link between wheel seal failures and semi-fluid grease?

ALEXANDRIA, Va. (April 13) — Fleet managers concerned about a connection between semi-fluid grease and wheel seal failures should find some answers by the end of September, when The Maintenance Council of the American Trucking Associations is expected to release a revised recommended practice on the issue.

RP 631, a maintenance standard concerning wheel-end lubrication, is being re-written to update lube-fill and inspection advice regarding semi-fluid grease. A revised standard has been approved in principle but is being refined. It should be finalized at TMC’s summer meeting in Indian Wells, Calif., in June. A 90-day “appeals” period will follow.

Fleets began using semi-fluid “00” greases in place of traditional gear-oil fills around 1995, aiming to cure rampant wheel-seal leaks and the resultant oil-contaminated brake shoes.

With its higher viscosity, semi-fluid grease largely cured the leakage issue and brought other advantages like extended seal life.

However, a pattern of catastrophic trailer wheel-end failures — or impending failures — was discovered within the last two years and was tentatively linked to the use of this lubricant, especially on tapered spindles.

While remaining somewhat mysterious, these failures are now attributed for the most part to wheel-end fill and inspection procedures. Unlike oil, it’s difficult for technicians to tell how much semi-fluid lube is needed and also to see how much is in the bearing cavity. And while oil presents a “waving flag” when a seal is failing — by leaking oil — the same is not true of leak-free semi-fluids. With the latter, the only way to be certain that the bearing has enough lube is to partially dismantle the wheel end.

The revised RP 631 will advise a four-level inspection regime beginning with the driver’s pre-trip routine, then a “detailed external inspection” to be done at PM intervals.

Level 3 would see lube condition checked by pulling the outer bearing, and the final level — a complete tear-down — would only be reached if abnormal conditions were found in the previous stage.