Any owner-operator who thinks of hubs and seals as merely the ends of his axles is in for a surprise. Of the many small but indispensable parts that keep a truck running, wheel seals, bearings and hubs are fundamental. Whether you pay a premium for low-maintenance equipment or buy products you will maintain yourself, understanding your hubs and seals can help you make buying decisions that will save money and minimize downtime.
Longer seal life used to require a lot of mechanical work by the owner-operator. Kurt Steffler, a 25-year owner-operator leased to Jones Motor Express, still does nearly all the work on his truck. He uses traditional hubs in all positions. Steffler says he has never had a bearing or seal failure with Chicago Rawhide seals, which he uses exclusively.
“An old-timer showed me how to put in bearings and seals and crank them down with a two-foot breaker bar,” Steffler says. “Of course, I check for heat on the hubs every time I get out of the truck and eyeball everything for leaks.”
Today, owner-operators who don’t want to replace bearings, seals and hubs can choose from a variety of packaged axles and wheel ends requiring very little maintenance and repair. Unitized wheel ends, the top of the line pre-set hub, are often assembled and put on an axle before being shipped to the truck manufacturer. Seal makers such as Chicago Rawhide and Stemco and bearing makers such as General Bearing, Timken, SKF and Freudenberg NOK supply their products to a manufacturer that engineers the entire preadjusted wheel end but also sells the bearings separately. Con Met engineers and builds hub assemblies. Low Maintenance System, or LMS, is Con Met’s name for its pre-set wheel end.
Rawhide seals, first used on stagecoaches in the 19th century, weren’t phased out until the 1950s. Today’s seals are made of polymers, which Con Met product manager Mark Wagner calls “engineered rubber.” Teflon, fluoroelastomers and nitrile rubber enable seals to last 300,000 miles or more. But seals and lubes must be compatible to ensure such longevity, says Dennis Henson, product manager for brakes and wheel ends at Dana.
Grant Sheldon, an owner-operator who tests products for Eaton, Kenworth and others, found that out the hard way. He still used rawhide seals into the late 1980s, using standard mineral oil as a lubricant and changing his hub oil every 30,000 miles. When he switched to synthetic lubes that promised extended maintenance intervals, the synthetics did not prove compatible with rawhide seals, which wore out quickly. He then switched to rubber seals and found they lasted 400,000 to 600,000 miles.
“They cost two to three times as much, but they last four to six times as long,” Sheldon says. “Using synthetic lubes and seals and preadjusted wheel ends saves money in the long run.”
But what exactly is a preadjusted wheel hub? Henson says they are distinct from traditional hubs. “Preadjusted hubs have engineered end play,” Henson says. “This allows the bearing end play to be established before the hub is installed. When the hub is installed on the axle by the truck or axle manufacturer, all that’s necessary is to tighten the spindle nut to the proper torque.”
Drive axles are somewhat less likely than other axles to have preadjusted wheel ends. According to Henson, some fleets do not find it necessary to use the more expensive, extended-maintenance preadjusted and unitized hubs because failure rates at drive axle positions are typically lower. Dana’s low-maintenance wheel end package for drives is available from several manufacturers, including Gunite. Drive hubs from Gunite, for example, have a drive flange oil fill design to “allow the use of lubricants that are compatible with today’s most popular differential lubricants,” according to the company. Gunite hubs are supported by a three-year, 350,000-mile warranty.
Meritor offers a unitized wheel end for drive axles that comes as a complete assembly with hubs, cam brakes and drums. The UWE-90 has four seals. The inner seal protects against brake shoe contamination. The outer seal keeps wheel bearing grease separate from axle lube, while a mid-hub and a spindle seal keep axle lube away from wheel bearing grease and brake shoes.
This unitized drive axle hub is made of aluminum, which adds price but makes the hub as much as 110 pounds per axle lighter than ductile iron hubs made by Meritor, Gunite and others. But Meritor’s Daytonlite ductile iron hubs improve tensile and yield strength and allow for much thinner hub sections.
The traditional hub is still common at all axle positions. Like the traditional hub, preadjusted hubs can use off-the-shelf seals and bearings. In contrast, when a seal or bearing needs to be replaced in a unitized hub, the entire hub has to be replaced. Thus, having a seal or bearing problem in the middle of nowhere with a traditional or preadjusted hub means a much easier fix.
It is likely, however, that fixing the problem will not return end play to exact specs. The advantage of the premium-engineered – and premium-priced – unitized hub is that it offers extended service intervals and longer life. Owner-operators will pay a higher price for Dana’s low-maintenance and other preadjusted hubs than for traditional hubs and even more for unitized hubs. In return they will save money and worry less that their seals or hubs will fail. Dana’s Outrunner seals carry a two-year, 200,000-mile warranty, while the company’s seals in low-maintenance hubs carry a three-year, 350,000-mile warranty. Because conventional hubs require proper bearing adjustment, lubricant cleanliness and seal and spindle nut installation, preadjusted and unitized hubs make sense to many thrifty owner-operators.
To say that bearings and seals are only as good as the lube they swim in may be an oversimplification, but the best lubes provide long maintenance intervals and life spans. Oil bath systems – completely fluid systems using no grease – were introduced in the 1960s to lessen the need to clean and repack bearings. But many shops found themselves with increased work and expense because linings were oil-soaked, and bearings were failing. There is a movement now back toward hard and semi-fluid greases because they do not exit the hub.
“Oil bath systems became popular because engineers mistakenly believed grease should move in the bearing environment.” Wagner says. Instead, “Grease should stick and bleed oil. This keeps the thickeners in grease from being degraded.” Wagner believes 50 percent of nondrive-axle hubs will soon be lubricated by hard greases. Semi-fluid grease has already regained popularity. Oil bath systems, however, have the advantage of weeping – leaving traces of oil on a hub that indicate a seal must be replaced.
Compatibility of lube and seal is complicated because seals are made of a variety of synthetic materials that can interact with mismatched lubes in less than desirable ways. To avoid this problem, Stemco Seals in Longview, Texas, requires SAE 50-weight lube in its seals for unitized hubs, says Marketing Manager Kara Bolster.
Other advances in wheel-end technology had to happen before longer-lasting wheel seals made sense. When inboard brake drums (mounted inside the wheel end) held sway, hubs had to be removed to service the brakes. This meant wheel seals had to be replaced each time. Outboard brake drums, however, do not require removing the hub, so the seal stays intact, and extended service intervals and longer life become important.
In an age when fewer owner-operators have the time, resources, will and skill to do things the old-fashioned way, low-maintenance and unitized hubs with precision-toleranced bearings, space-age seals and properly matched lubes become more valuable as a way to save money and reduce downtime.