Medium Duty: Gears and Grease

Getting up to speed on TMC PR655: Drive-Axle Maintenance Guidlines.

In a world where computers and touch-screens seem to rule the maintenance shop, inspecting and maintaining a drive axle may not seem very exciting. But there aren’t many components more crucial to a truck’s mission, and a new Recommended Practice (RP) from the Technology & Maintenance Council (TMC) shows how to keep your drive axles pushing your trucks down the road for many trouble-free miles.

TMC Recommended Practice 655 sets out Drive Axle Maintenance Guidelines for Class-6, 7 and 8 trucks, but our axle experts say the principles apply to medium-duty trucks as well. In fact, in some ways the demands on a medium-duty drive axle are tougher than those placed on a heavy-duty drive axle.

“There’s a section in the RP that calls out different vocations” says Steve Slesinsky, director of product planning, Dana Corp. “There’s a city delivery and school bus vocation called out which would require checks and maintenance intervals more often.

“In general, medium-duty applications tend not to be as highly loaded as on-highway Class-8 axles, but they do see a different duty cycle with more stop-and-go,” he says. “So there could be a potential for more loosening or more wear-out conditions, not because they’re overloaded, but because of their slow-speed, stop-and-go operations.

“Another issue with medium-duty vehicles is, you tend to get less-skilled drivers, whereas I would classify Class-8 drivers as very professional and knowledgeable about the whole vehicle,” he says. “In medium-duty applications, the driver/operator may not be as familiar with the vehicle. It may be a temporary person driving the vehicle.”


After settling questions of axle parts nomenclature (needed so technicians, parts suppliers and OEMs can understand each other when discussing components), RP 655 digs right into a list of key maintenance guidelines. We went through the list and asked axle experts to expand on the RP’s recommendations.

“There’s enough commonality out there among commercial vehicle axles, so whether it’s one of ours or one of our competitors, there are some basics you need to do right,” says Dana’s Slesinsky. “For example, visual inspections to make sure there aren’t leaks, cracks, weeps, anything that can be easily observed with the axle. Those conditions could exist. And then, going along with leaks or weeps, making sure that the oil level in those axles is maintained. Just like you would in your engine to make sure your engine oil level is up, having the proper lube levels maintained in your axles is important for the longevity of the axle.”

“If you did have a leak—say a wheel seal were leaking—and over time it diminished your axle lube, you’d get oil on your brakes, but you’d also be starving oil from the drive axle gearing,” Slesinsky explains. “So, you go from a simple fix of replacing a wheel seal to possibly having to replace an entire axle gear assembly, if you ran the axle low on lubricant.

“If you run an axle low under load, you could cause damage to the gears and bearings, which could cost you some life on your axle,” he warns. “If you ran the axle low on lubricant, you’re probably going to have to get it into the shop and look at rebuilding the axle.”


Checking for leaks and lube levels may seem like a no-brainer, but the kind of disaster scenario that Slesinsky describes actually unfolds with alarming regularity.

“Checking lube, we kind of take that for granted, but we don’t have a week that goes by that we don’t see a claim for a component that’s out of fluid,” says Charles Allen, director of global customer service for commercial vehicle systems for ArvinMeritor. “There could be a seal leak that’s been allowed to run for a long period of time because nobody has taken the time to go under the vehicle to look at it. A fluid leak could be addressed pretty quickly, but if it’s allowed to run to the point where it depletes the fluid, then it’s a pretty expensive repair.”

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