Medium Duty: Gears and Grease

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

“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

We Recommend