Medium Duty: Gears and Grease

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.”

One way to avert such a disaster: looking for loose fasteners.

“Obviously,” says Slesinsky, “one of the first reasons you might see a leak is that some fasteners came loose. So, if you see a leak, before you go thinking there’s a failed part, it may be a loose part. That’s something to consider before you go looking for a major problem that may not exist.”


RP 655 gives recommended lubrication change intervals (see chart on p. 16) as well as lube analysis guidelines, but our experts have some additional guidelines as well.

For instance, Slesinsky cautions that some technicians don’t differentiate between regular lubricants and extended-life lubes, an oversight that could add unnecessary costs to your maintenance checks.

“With some of the extended and premium lubricants that are available on the market, such as synthetics, don’t change the fluid in an axle that uses extended-drain lubricant as often as you’d change a petroleum-based oil product,” he warns. “There’s actually some savings if they understand they have an extended-life lubricant product in that axle: Don’t spend the $200 changing the lubricant; leave it in there as it was intended.

“The other thing on that chart is that some axles that use a lubrication pump also have lubrication filters that are mounted on the outside of the axle,” he says. “Those types of axles require that filter to be changed every 100,000 miles, as well as to top up the lube. So, there’s a little more information required if that axles happens to use a pump with an externally-mounted filter.”

Maintaining those intervals can often depend on regular lube analysis, according to ArvinMeritor’s Allen.

“In a lube analysis, you’re trying to do some predictive maintenance,” he explains. “You may not have any leaks, and the fluid level may be where it needs to be, but by performing a fluid analysis, you can look for things that aren’t visible to you, that aren’t readily apparent to you, and you get to head them off early.”

“Fluid analysis does a couple of things for you,” says Lee French, technical support manager for ArvinMeritor. “It gives you an early warning if there is something’s going on, and it tells you how the lube is performing. Over time, you can get a good idea what sort of mileage or time frame you can run for.

“There are certain key parts of a lube analysis that you look for, like your silicon content and such,” he explains. “You’ll get an idea how the additive package is performing, and whether the lubricant is good for continued use.”


For many medium-duty vocational trucks, setting maintenance intervals by mileage just doesn’t make sense. Vocations with low mileage accumulation might be better served by maintenance intervals based on hours of service.

“That goes back to the value of the lube sample,” says French, “because that will give you an idea how that lube performs for your particular application. Our specifications are based on mileage or time interval; it gives you the max for both, and if the maintenance intervals happens to be less, that’s great. It never hurts to take a peek at it more often.”

According to Allen, setting axle maintenance periods by time shouldn’t complicate the routine if your trucks have other, mileage-based maintenance intervals. ”Can you harmonize those points so that you hit them all at the same time?” he asks. “A lot of times, there’s enough flexibility to be able to do that. I think there’s enough latitude in the way we’ve laid out our maintenance schedule that you could make these points coincide with other maintenance points or intervals that you’d be performing on the vehicle.”


Is it possible to keep your trucks too clean? RP 655 cautions against getting too close to drive axle components when doing high-pressure washing.

“You can do some damage,” Allen admits. “In general it’s not a good idea (to spray the axle), because you have the potential with a high pressure wash of driving contaminants under the excluder lip and into the seal. That could be an input seal, output seal or wheel end seal, and with regard to a breather, there’s probably an opportunity to drive some moisture into an axle with a pressure washer.”

“The seal design has features built into it to minimize the susceptibility to that,” says French, “but it is a high-pressure washer...”

“In a lot of cases we put in a deflector to try to protect the seal,” Allen says, “but if you get some direct hits—if someone decides, ‘Hey, I want to get right in there,’ you can do some damage.”

RP 655 also cautions technicians to be alert for seal leakage, vibrations and noise, all signs of excessive end play. “That’s in there to insure that the repair is done correctly the first time, and that it’s long-lasting,” French explains. “If the seal was leaking because of end play, and you replace the seal, you haven’t fixed the problem. It’s hard to say what could be causing the end play without looking at the unit, but you could have oil contamination problems.”

“You could have a nut that’s backed off, so the bearings have lost their load, and the shaft could come loose,” Allen echoes. “If you simply put another seal on there, you’ll very likely have a repeat failure, because you haven’t addressed the root cause. The key thing is, don’t just fix the symptoms, go and address the root cause.”


Over and above the RP, our experts recommend careful spec’ing of drive axles to meet the needs of the truck’s application, using only genuine replacement parts, and, of course, following the manufacturer’s recommended maintenance procedures.

“Operate the component per the prescribed maintenance schedule that the manufacturer has, whether it be our product or someone else’s,” says Allen. “That goes for intervals, and that goes for fluids, in the case of lubes: Lubes are a key part. Lubes are as important to the performance of a component as the specification of a bearing, so make sure you use recommended fluids.”

A lot depends on the technician, though. You need to know that you’ve got the right tech on the right job, according to Slesinsky.

“In the fleet maintenance shop, there are certain levels of expertise,” he says. “You might have someone skilled in wheels and tires, you might have someone skilled in alignments, you might have someone skilled at electronics. I think the ones that are doing the oil changes and the lube jobs are probably also the next level up that would do the wheel end work, and would probably be more familiar with the axles. The people more skilled in electronics and diagnostics would be more skilled in engine work and transmission work. People who have their heavy-duty maintenance certificates should be very familiar with these processes and procedures.”

For more information on RP 655 and other Recommended Practices, go to


Vocation: City Delivery, School Bus, Fire Truck, Motorhome

  • Check Oil Level and Breather—Every 10,000 miles (16,000 km), once a month or the fleet maintenance interval, whichever comes first.
  • Petroleum-Based Oil Change on Axle With or Without Pump and Filter System—Every 50,000 miles (80,000 km) or annually, whichever comes first.
  • Approved Synthetic Oil Change on Axle With or Without Pump and Filter System—Every 100,000 miles (160,000 km) or annually, whichever come first. NOTE: This interval applies to approved semi-synthetic and full-synthetic oils only. For a list of approved oils, refer to the axle manufacturer’s approved oil list
  • Filter Change on Axle With Pump and Filter System—Every 100,000 miles (160,000 km).

Source: Technology & Maintenance Council RP 655