Medium Duty: Gears and Grease

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

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.

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