WHICH COMPONENT is most important in a wheel-end system: the spindle, spindle nut, hub cap, hub, seal, lubricant, or bearings?
Every component, according to Michael Colmenero, Stemco's product engineering manager.
That's because a premium seal can't overcome a poor hub cap, a premium bearing can't perform without clean lubricants, a premium lubricant can't overcome a poor seal design, and seal and bearings can't perform without proper end-play adjustment.
“It's very critical that all these components work together,” he said in the CTEA's lubrication presentation, at which he was joined by three other speakers. “You cannot just expect one component to compensate for the performance of the other components.”
He said lubricants include oils (petroleum-base mineral and synthetic) and greases (hard-pack #2 and semi-fluid 00). The purpose is to reduce friction and wear, disperse heat and wear particles, and protect against corrosion.
He said lubricants consist of a base oil plus additives dispersed in a thickener. The base oil determines if the grease is mineral or synthetic, and provides the lubrication. The thickener holds the grease where lubrication is needed, and may or may not be synthetic.
“Greases do not cool as well as oil, do not flush the wear area as well as oil, do not stay where the lubrication is needed better than oil, and usually are easier to seal than oil, and may contain EP additives,” he said. “Synthetics cost more than non-synthetics, and come in a variety of consistencies.
“Which lubricant is better? It depends on the application and individual shop preference.”
Seal retains lubricants
He said a seal keeps contamination outside of the wheel-end cavity and retains lubricants within the same cavity (oil and grease). He defines contamination as “any material or substance foreign or naturally occurring in a wheel end that will hinder the proper function or degrade the life of components in that system.” External examples would be dirt, grit, sand, salt, mud, water, and ice. Internal examples would be rubber debris, metal debris, salt/solvent, and rust.
Colmenero said that on a trailer axle, contaminants come from the external environment, seal, bearings, and axle tube; on a drive axle, from the external environment, seal, bearings, axle tube, axle vent, gears, and pinion input and output; on a steer axle, from the external environment, seal, and bearings.
“Internal contamination on an axle tube includes slag containing oil, metal, water, and rust,” he said. “If the axle is unplugged, the vibratory action can force contamination into the wheel end. Rust forms when water condenses in the tube.”
The contaminant types: a water/oil mixture may be gray or milky colored, and a spatter test will positively identify this; with rubber debris, the seal assembly, components, and the lube itself must be inspected; with metallic, an inspection of the bearing should show abrasive wearing, pitting, grooving, or damage to the cage or rollers, and a magnet should be dragged through the lube; dirt and mud show similar, but less severe, effects to that of metallic; salt and solvent show excessive corrosion.
He said the barrel angle on a radial lip seal should be between 20 and 35 degrees. If it's too low, it causes accelerated wear and shorter seal life. If it's too high, proper contact geometry will not occur.
The flex thickness should be between .024" and .060". If it's too thin, there are de-molding/strength issues. If it's too thick, there is an increased radial load.
The “R” value should be between .010" and .020". Negative “R” values could result in excessive wear.
He said a short beam length increases radio load and wear of the lip. A long beam length increases flexibility and conformity. The head thickness maintains the stability of the sealing lip and positions the spring properly.
“Venting is critical,” he said. “There's a relief of pressure and vacuum in the wheel end. That maximizes seal life.”
The four “Rs”
In his presentation on lubricant requirements for bearings, Petro-Canada sales manager Clint Domanski said that regardless of the application, the four “Rs” are still paramount: the right lubrication, the right place, the right amount, and the right time.
He said there are three basic configurations for the lubrication of wheel-end hub assemblies: oil-lubricated, unitized or filter-life hubs, and grease-lubricated.
He said most wheel ends have a similar layout: two sets of tapered roller bearings with an inner and outer set. There are two basic types of wheel ends: driven, which are commonly on the front end and use gear oils to account for the required gearing protection; and non-driven, which are most often on the trailer end of vehicles and can be lubricated by oils or greases (soft or hard).
“For oil-lubricated hubs, grease is standard in Europe,” he said. “The most common oil in use is API (American Petroleum Institute) GL-5 for driven axles.
The most common oil viscosity is 140 centistokes at 40 degrees C. Simple oil is often the best form of lubrication for these applications. The key is to insure the fluid level is correct and maintained, and the seals are functioning to minimize leakage.”
He said the most common viscosity of gear oils is 80W90, with Canada having a particular need for 75W90.
Domanski said that over 90% of steering hub driven wheel-end assemblies use an oil, most commonly a gear oil, and the service interval is in the 250,000-mile range.
“In the late ‘80s, we saw the use of softer or double-zero greases for wheel-end lubrication,” he said. “This was an attempt to resolve the issue of leaky seals and the safety issue. When done properly, soft greases decrease seal leakage and extend service life two to three times. They tend to slump and can migrate, so proper fill levels are critical to ensure the inner and outer bearings are adequately lubricated.
“Heavier-based oil in a synthetic can give a thicker oil film on bearings, so it does provide some enhanced protection. However, a heavier base also causes more internal friction, so the use of synthetic, heavy-based oil grease may operate at higher temperatures. When using a soft grease, service life can be extended. However, the real need is to ensure sufficient grease for all bearing components. If a hub has less than what is required, some migration can occur. Checking the bearing axle is a good indicator.”
He said unitized hubs most often are sealed for life, so there's little maintenance or re-lubrication required.
The third type of hub assembly, grease-lubricated, uses straightforward lubrication. At the appropriate service intervals, the bearings are removed, steam-cleaned, and repacked with the correct grease.
“It's most important to get the correct level of grease in the housing,” he said. “Once the bearing grease is packed, the housing is filled with one-third volume of grease.
“Not all wheel-bearing greases are the same. NLGI (National Lubricating Grease Institute) defines the softness or stiffness of grease. The smaller the number, the softer the grease — 00 and 000 are the softest. All wheel-bearing greases are EP (extreme pressure) greases. The standard practice in Europe is to use a #2 grease.”
He said lithium base and complex greases make up 65% of the marketplace.
“They have a lot of nice properties: they're stable, have excellent water resistance, and a wide range of temperature use, so most grease suppliers recommend lithium greases for bearings,” he said.
“Grease is a more forgiving lubricant. It stays in place so it's less tied to leakage, and it does allow for longer re-lubrication intervals. It does have less of a cooling effect so it's more difficult to monitor the condition of the systems in operation. A higher-based oil viscosity we see in synthetic soft greases will sustain that thicker oil film, but you will get higher operating temperatures. In many cases, an EP2 grease, lithium base with medium-range viscosity, seems to offer the best compromise for wheel bearings for the required properties and maintenance practices we see.”
Film of oil
What do you see when you put a bearing surface under a high-powered microscope? A series of peaks and valleys.
“In order for any bearing to operate with surfaces with that degree of roughness, they must have a film of oil separating the two surfaces,” said Timken sales engineer Bill Ratcliff. “That film of oil needs to be no greater than 100-millionths of an inch. Pretty darned thin, but you must have that or that's when you see smoke in the mirrors of your truck and you get a burnout.”
In his presentation on lubrication of trailer wheel ends, he said there are three basic ways to achieve that oil film:
- Oil bath.
“Fifty years ago, all wheel ends cast with inboard brakes and friction material didn't last long,” he said. “The idea of running a wheel end on oil made it much easier to do an inboard brake job. And hence the beginning of oil bath lubrication back in early ‘50s. All fleets grabbed onto this idea because it was a timesaver and oil seals only had to perform as long as the brake lining. It is more difficult to seal liquid oil than a #2 grease. An oil is sensitive to installation. It must be done properly and it does require frequent monitoring. It lasts four times as long as it did 40 years ago.”
- Semi-fluid as grease.
“In the mid-‘90s, lubrication companies said, ‘We've got semi-fluid grease in our lineup, and its main purpose has been for auto greasers. But we know it won't leak as much as oil, so why don't we start promoting it for wheel ends?’ The industry in general didn't do its homework. Someone at the beginning made the decision that if you put the same amount of semi-fluid grease in there as you did oil, it would work the same and be OK. But two years later with wheel-end issues, they decided, ‘Ooh, maybe we ought to put more in there.’ It was determined that if you put the right amount of semi-fluid in there, it will operate satisfactorily if it's half full. It won't leak as much as oil.”
- #2 grease.
“This is the most common way. Drive wheels are even doing it in certain instances. And you'll see it in greater volume. There are some advantages. A grease seal is self-venting, so there's no need for an external vent. It requires minimal maintenance. It provides constant lubrication.
It requires little extra time to install.
“We at Timken have always said that the base oil viscosity of the grease you use to lubricate wheel bearings should be anywhere from 150 to 220 centistokes at 40 degrees C. Any oil seal must have the lid facing toward the lubricant side because that's only way it's going to retain the oil. And because it's facing toward the lubricated side, it must have a vent, because as the temperature rises, pressure rises and pressure, if it can't vent, will push down on the lip and cause it to leak. With a grease seal, the lip faces in opposite direction because the purpose is not to retain the grease but to keep contamination out. It's called an excluder seal. When the temperature rises, pressure vents through seal and out.”
His suggestions for an annual inspection of a trailer:
- “Crawl underneath so you can rotate it one revolution and take look at the seal. Is there any fresh lubricant coming out of it, or does it look dry and dirty?”
- “Listen to the wheel bearings. Take a simple piece of flexible water hose about 1½“ in diameter, hold it to your ear and place it near a hubcap and spin the wheel by hand. If there's anything going wrong on the inside of that wheel end, especially bearing-related, you're going to hear a difference in sound.”
- “How does it feel?”
- “Get an extendable magnet and stick it in there as far as you can, smell the oil at same time and what is on the end of magnet? Anything? Or just clean oil? Beause if you have a bearing starting to deteriorate, you're going to get metal filings.”
Automatic lubrication system
Beka Lube Equipment's Andy Olesh said everybody is trying to sell commodities, but few are really thinking about the end users.
“It seems like the bottom line is price,” he said. “But by adding value to your product, you might be able to get the dollar amount you're looking for.”
He said the EP2 automatic lubrication system dispenses small, calibrated amounts of EP2 grease to various components at regular intervals. It provides these components with continuous lubrication while in motion, and that ensures all components are lubricated while in a working state.
“This is important because you want full coverage of all components,” he said. “If you're manually lubricating and the equipment is stopped, you're packing a bearing or a component but not necessarily getting that full rotation.”
The system consists of a pump and control unit.
“You only need to refresh the grease, and not replace it, as the grease does not run out,” he said. “EP2 greases are thicker and now have that staying power.
“Automatic lubrication is the only way to ensure all components are being lubricated correctly. There are many good mechanics, but they can't be there twice a day to lubricate, or four times a day if you're running through sand or mud.”