Wheel-End Wisdom
Deborah Lockridge
Senior Editor
"When I started out 22 years ago, axles needed bearings at 250,000 to 300,000 miles," says John Hinesly, western regional manager for ArvinMeritor. Same story for engines. They needed an in-frame overhaul after only a quarter-million miles.
These days, Hinesly says, "linehaul axles are really built to run a million miles."
Just like engines.
But that doesn't mean you can ignore them.
While there's not as much active maintenance on today's axles and wheel-ends, you do need to check them regularly to make sure minor problems don't turn into expensive repairs.
"Whether it's a traditional system or one of the advanced systems, it's still key to observe what you've got," says Tom Smego, director of sales at SKF/Chicago Rawhide. "The perception is the systems are Ômaintenance free.' We tend to fall into the trap of [thinking] ÔI buy it and never look at it again.'"
The first line of defense is the driver's pre-trip inspection, says Todd Anderson, vice president of engineering at Stemco. "For most wheel-ends, that's nothing more than walking to the wheel-end and examining it, looking for signs that oil may have escaped, out the seal or through some of the hubcap area, looking for oil that may be on the brake shoe. If you can see any lubricant that's escaped the hub cavity, that may lead you to pulling the hubcap off and investigating a little closer inside the wheel-end."
In an oil-bath system, drivers should check the lube level by looking at the fill line on the hubcap. Drivers should also be on the lookout for a milky or cloudy appearance to an oil-bath lube, which could indicate water contamination.
As part of your PM schedule, raise the vehicle off the ground for a more thorough inspection. Remove the hubcap and check for end play. Make sure nothing has loosened, and that the hubcap isn't cracked or dented. Check for smooth rotation and any abnormal wobbling that could indicate problems with bearing adjustment or rollers. On steer axles, carefully check all steering, suspension and frame components.
Check for leaking seals. ArvinMeritor's Hinesly recommends not only checking around the seal surface and the input and output shafts, but also looking up at the frame. It's not uncommon, he says, for the air flowing underneath a truck at highway speeds to blow the lube away from the axle, disguising leaks.
Proper alignment is also important to maximize component life. Tires should be balanced, tire diameters matched and tire pressure maintained.
It's important to keep complete, accurate maintenance records. These can provide a quick indication of how axles and other components are holding up. When something does go wrong, make sure technicians are doing proper troubleshooting and paying attention to detail.
Wheel-end Assembly
"I think some of the biggest issues in regards to wheel-ends are installation related issues," says Steve Slesinski, director of product planning for Dana.
Whenever you have to perform service on the wheel-end, whether you're replacing seals, bearings or working on brakes, it's vital to reassemble the wheel-end correctly, including installing the components correctly, getting the bearings seated, the right bearing adjustment and the right amount of lubricant.
"There are varying degrees of how well fleets meet that challenge," says Stemco's Anderson. "I know quite a few fleets who pay a lot of attention to wheel-end maintenance and do an excellent job. There are other fleets who don't pay as much attention and have a higher percentage of problems."
When you take apart a wheel-end, it's important to thoroughly inspect and clean everything, says John Butler, a field service representative with Federal Mogul.
"This is absolutely essential, and a lot of people don't do it," Butler says. "Anytime you leave anything inside a wheel end, it will cause you grief. Worn metal particles or contamination can cause the seal to fail." Rust on the hub bore or spindle must be cleaned off. "You don't have to get the pits out of it, but you have to get that rough slag off. It impedes the seal from sealing. It also makes it stick so when it's time to take it off, it might take you two sticks of dynamite."
Inspect the studs that hold the wheels on the hub, says Al Anderson, fleet sales manager at Consolidated Metco. It's important to make sure they aren't stripped or loose in the hub, so they will hold the wheels once you put the lug nuts back on.
If the seal is not installed correctly, the wheel-end performance can be compromised and the life of that wheel-end could be shortened, says Stemco's Anderson. While installation procedures differ somewhat depending on the manufacturer, he says, with any method, it's important to make sure the seal is fully bottomed out, or fully seated, in the hub bore or on the spindle shoulder. If the seal is cocked, with one side higher than the other, it will result in uneven wear on the seal.
Once you have the seal in place, it's important to be careful during reassembly of the components. "People will install a new seal into a hub, place the hub on the spindle, then pull it off again for some reason," says Dana's Slesinski. "Many times when they do that, they actually damage the seal without knowing they did so." The outer end of the hub needs to be properly supported as it is placed back onto the axle or spindle.
The right amount of lubrication is also vital. If you're using grease, you have to pack the bearings; if you use oil, pre-lube them. After assembly, it's essential to fill the hub cavity with grease or oil. Especially on drive axles, forgetting this step can cause catastrophic failure, Butler says. "It takes about 30 minutes for the rear end to provide enough lube, and in the meantime, you can weld the bearing to the spindle."
Bearing Adjustment
Probably the biggest bugaboo in assembling a wheel-end after service is bearing adjustment.
"I always joke that if you ask 10 different people how to do wheel bearing adjustment, you're going to get 12 different answers," says ArvinMeritor's Hinesly. "Everyone has a little different tweak on it - what they think works for them."
Al Anderson, fleet sales manager with Consolidated Metco, says the importance of wheel bearing adjustment is grossly underestimated by many fleets.
"It might not seem like a huge deal, but think of the consequences," he says. "Minor consequences include wheel seal leaks and wheel bearing failures. Major consequences are wheel run-offs." If a wheel gets out into the motoring public it could hit another vehicle, often with tragic results.
To address the bearing adjustment issue, the ATA's Technology and Maintenance Council several years ago developed a Recommended Practice, RP-618. The key factor of the RP is using a dial indicator to measure wheel-end adjustment, which should measure no more than 5 thousands of an inch of end play. "It's like boiling water," says Smego. "You know it's hot, but until you put a thermometer in it, how hot is it? Until you put a gauge on the wheel-end, you don't know how much end play you have."
Too tight is worse than too loose, says ConMet's Anderson. "Loose results in a much more gradual failure. Typically you'll get a wheel seal failure before you get a gross bearing failure, so it gives you an opportunity to get it right. If you have something too tight, it fails rapidly. You will not get an early warning."
Hinesly recalls a visit to a fleet where a shop manager assured him his shops were doing proper bearing adjustments. The manager even bet Hinesly lunch that they could pick any one of his shops at random and visit for confirmation. When technicians at the selected shop - touted as the fleet's best - had to go find the dusty magnetic dial indicator and couldn't describe the proper procedure for adjusting bearings, Hinesly had a free lunch.
ConMet's Anderson notes that trailers tend to get less maintenance attention than tractors, yet many dangerous wheel-off incidents occur on trailers. "You hear a lot of drivers say, ÔI didn't even know the thing came off,'" he says. "You'll sometimes see a trailer show up with one of the duals completely gone."
Stemco's Anderson notes that some people are installing their wheel-ends using preload as part of the bearing adjustment. However, he says, "once you install preload, there's no way of measuring how much you have, so if you over-tighten it, you won't be able to tell if it's over-tightened, and you can cause damage to the wheel-end. So if a fleet decides to install a wheel-end in preload, it's important for them to clearly understand the procedure to result in the right amount of preload."
Properly adjusted bearings also help resolve another traditional wheel-end problem: leaky wheel seals. Wheel seals, Smego explains, are the weak link in the system. Leaky seals, he says, are a telltale sign that something's wrong in your wheel-end.
"RP 618 on bearing adjustment gave the industry a unified bearing adjustment standard to work off, and I think that helped solve the issue of leaky wheel seals, no matter whose seal it was."
Before that, he says, the right way to adjust bearings "depended on which supplier or vendor you talked to last."
Not everyone signs on to the dial indicator procedure. Federal Mogul, for instance, has a patented device that it claims is a more accurate way of measuring end play. The key, says Federal Mogul's Butler, is to have a good procedure and stick to it.
Lubrication
ArvinMeritor's Hinesly recalls one fleet customer who had to replace both front and rear differentials in six trucks after the ring and pinion teeth were worn to a sharp knife edge. The culprit? Two 55-gallon drums of GL-3 oil, rather than the GL-5 required. "It was the same viscosity, so he thought he was buying the same lube, but he did not look at the GL specification," Hinesly says. "GL-5 refers to the additive package. When you're under load, it helps perform that bond between the ring and pinion."
In general, you should use the lube specified by the OEM and axle manufacturer, use the proper amount of lubrication, follow the lubrication-change interval or schedule for the axle, and - if the axle is equipped with oil pump and filter - replace the filter when the lube in the axle is drained and replaced.
There are some tricks to knowing you're using the right amount of lube. For instance, says Stemco's Anderson, if you're using oil bath lubrication, it takes a little time for the oil to work its way through the bearings as the wheel-end is filled. So as you fill that wheel-end, you may need to take a little time to let it settle in and work its way through the bearings, then come back and check the level again.
To get the right amount of semi-fluid grease, many fleets measure or calculate how much semi-fluid grease is needed for that application, then meter out that volume or weight in the shop to take away much of the guesswork.
If you're using hard-pack grease, it's important to properly pack the bearings and make sure there's enough grease around the bearing rollers, and fill the sump of the hub cavity in the wheel-end.
Check fluid levels whenever the engine oil is changed. Don't make the mistake of checking the oil level by dipping a finger through the fill hole and think that if you feel oil, the axle is full, says ArvinMeritor. Oil should be at the same level as the fill hole in order to fully lubricate all necessary components. If the oil level is extremely low, look for leaks.
Spec'ing an oil or lubrication pump for drive axles, where available, provides additional protection, particularly against spinouts. The combination of a pump and filter can further increase lubricant efficiency.
Synthetic lubes mean you don't have the change the axle oil for 250,000 miles or more, and most linehaul fleets, Hinesly says, go up to 500,000. However, he says, it's a good idea to analyze the lube at that 250,000-mile mark. "You might see if a bearing is breaking down or if you've got some water contamination in the lube."
Water contamination is often a problem for truck owners who like to keep their equipment squeaky clean. Spray from high-pressure washers can get through some of the vent systems on the wheel and let water into the wheel-end.
Hubs & Wheels
"One of the biggest mistakes people make is thinking that a torque wrench is connected to an air hose," says Paul Levering, vice president of technical services at Webb Wheel Products. "By that I mean, an impact wrench is not the same thing as a torque wrench."
Webb and other wheel manufacturers specify a torque range for wheel fasteners that needs to be checked with a manual torque wrench. Generally, Levering says, people put more torque on with an impact wrench than they realize. If you over-torque the fasteners, you can stretch the stud to the point of almost failure and not know it. On the other hand, if it's under-torqued, the wheel can move on the hub and cause wheel stud failures. Either way, you could be looking at wheels that come off and become deadly projectiles on the highway.
"Once a wheel starts to come loose, nothing good happens," Levering says. "At the very least, you're going to damage the hub and wheel, and it could have far more serious consequences."
Painted wheels are another culprit of loose wheels, Levering says. If the paint is too thick, or not allowed to cure properly, it will compress. "Some paint takes a couple of days to cure, but mechanics will let it sit for only 30 minutes," he says.
With hub-piloted wheels, it's important to inspect the fasteners - both the nut and stud - when you take the wheels off. Make sure they're in good condition, that the threads aren't rusty. Before you put the nuts back on, put a drop of oil in the thread of the nut and in between the nut and the washer. Levering says if you have rusty threads or rusty joints, even with the right amount of torque, you won't get the right clamp load. Torque ratings are made on the assumption that all the components are in good condition; if they're not, it throws things off.
In its 1992 report on wheel loss accidents, Levering says, the National Transportation Safety Board found that a large percentage of wheel-off incidents occurred within 30 days of servicing the vehicle - showing the important of proper maintenance procedures.
To help develop those proper procedures, ConMet's Anderson notes there are many other TMC Recommended Practices that speak to wheel-end issues such as lubricants and other maintenance items.
Spec'ing For Low Maintenance
One way to address some of these issues is by spec'ing newer components designed to reduce or eliminate the potential for mistakes. Front non-drive steer axles, especially, are increasingly being spec'd with some level of low-maintenance components.
Some axles feature permanently assembled, sealed and lubricated hubs. ConMet's PreSet hub assemblies feature pre-adjusted bearings that use a spacer to positively set the bearing clearance, eliminating the need for traditional manual wheel-end adjustments. Similarly, Dana's LMS, or Low Maintenance System, combines a precision machined hub, premium wheel seal, premium bearings and precision spacer in a self-contained unit that can be torqued up to a predefined level; no bearing adjustment needed.
Going a step further, unitized hub, bearing and seal assemblies make wheel bearing, seal maintenance and wheel-end adjustment unnecessary. However, individual components can't be serviced. If a seal goes in a unitized hub, the whole hub unit must be replaced.
Depending on what type of system you choose, you could be looking at tens of dollars to hundreds of dollars more in price. Whether that investment will pay off in reduced maintenance costs is something you have to analyze for your fleet.
