Hot hubs, cool lubes

August-September 2019

Tom Berg


“Thermal events” might seem an amusing euphemism for “fire,” but they’re not so funny to people who own trucks that have been burned up because of them.

Fleet-manager members of the Technology & Maintenance Council of the American Trucking Associations have formed a task force to investigate such happenings, but some causes are known. These include dragging brakes and underinflated tires that go unnoticed by drivers, especially when they’re on trailers 60 or more feet behind them.

Another less frequent cause is overheated wheel ends, which can occur because of insufficient lubricant in hubs. Roger Maye, national service manager for Consolidated Metco, a major maker of wheel-end equipment, says these are easily preventable through a few simple steps during a driver’s pre-trip, enroute and post-trip inspections, and preventive maintenance inspections of the vehicle.

Before and after a trip, visually check lubricant condition and quantity on steer and trailer hubs lubricated with oil. This inspection is very quick if the inspection window on the hub cap is clear. Wipe the inspection window clean with a shop rag if necessary. Also check for leaking wheel seals as part of the inspections, Maye said.

En route, periodically check the temperature of the hub with an infrared thermometer or simply by placing a hand on one hub, then others nearby to compare the temps. (Be careful so you don’t burn yourself!) You’re looking for abnormally high temps, where the maximum safe operating temperature of a hub assembly is ambient temperature plus 150 degrees.

Drive axle hubs and trailer hubs lubed with semi-fluid grease should be inspected during scheduled PM inspections. Lubricant in drive axle hubs can be inspected by removing a sample through the fill plug in the hub.

Oil contaminated with moisture will appear milky, he said. If there are questions about possible moisture contamination, do a simple “crackle test” by placing a small sample of the oil in a metal pan. Heat the pan, and oil will smoke, but moisture-contaminated oil will crackle and pop when heat is applied and the moisture turns to steam.

Annually, check trailer hubs lubricated with semi-fluid grease by removing the hub caps, and inspect the lube for condition and quantity. Be sure the ends of the bearing rollers are covered with grease. Refer to the hub manufacturer’s service instructions if service is required. There are a variety of wheel end lubrication options in use today, ranging from CD50 to 85W-140 oil, and semi-fluid or Grade 2 grease, Maye says. Each of these lubricants has specific characteristics. Consult with your lubricant and hub manufacturer to determine the best product for your specific application. LL