NASHVILLE, Tenn. – A new Recommended Practice for using semi-fluid grease in wheel ends is now the rule presented by the Maintenance Council of the American Trucking Associations. But the maintenance procedure (known simply as an RP) may also have dealt a blow to one of the product’s original selling points.
The fact that the grease now has to be filled to the 3 and 9 o’clock positions in a hub cavity – roughly straight across centre – isn’t much of a change. It’s simply a little more grease than had been suggested with the 4 and 8 o’clock positions used by those who pour traditional oil into a hub. But now users are told also to check the fill levels every 100,000 miles (160,000 km for the metrically inclined), and that could dampen the long-life properties that tend to come with synthetic versions of the grease.
“You have to pull the outer bearing,” explains Henkel Corp. engineer Bob Tanis, who led the review of the maintenance practice. “It’s not a low-maintenance item any longer.”
For awhile, the mere use of the grease appeared to be a high-maintenance issue on its own. When enough lubricant wasn’t added, bearings ran dry and in some cases that led to the dreaded loss of truck wheels.
Issues of leaking oils had been solved, but that did nothing to address problems that appeared if installers followed traditional fill procedures designed for oils.
A growing number of failures all had three things in common, says Tanis: tapered spindles, low grease levels and the use of semi-fluid grease.
“It would work if you make sure you have enough in there, but if you want the best recommendation, it’s not the best,” Tanis insists. “If I had my druthers, I’d use transmission lubricant. It’s the most thermally stable lubricant in the entire truck.”
But ExxonMobil – whose Mobilith SHC 007 dominates greases used in this application – is working with individual component manufacturers to refine the rules, undoubtedly to find a way to retain the long-life attributes that come with a synthetic lube.
“The requirement for the inspection is a very valid one,” says ExxonMobil OEM sales manager Sam Hughes, adding that a check of bearing endplay is probably the “key” reason for inspections. “The RP is as good a general guide as you can get.
“We’re saying utilize good practices and check with the OEM … the use, the application of the product does not circumvent sound maintenance practices.”
ExxonMobil is recommending a “post audit” on a few hubs after about three months in service, checking axial endplay and actually measuring the amount of grease in a hub if there are any lingering questions. But it’s questioning whether entire wheel ends always need to be pulled apart.
Despite initial failures linked to installation problems, some fleets continue to embrace the use of semi-fluid grease over oil. Sales continued to rise even when the issue was not yet resolved, Hughes adds.
“In our business, Mobilith SHC 007 has virtually eliminated leaky oil seals, which has dramatically reduced the number of our trailers that are taken out of service,” says Jerry Thrift, group manager of maintenance services for Ryder Transportation Services. “Ryder began using the product three years ago, and now it’s in 15,000 of the company’s 46,000 trailers.”
Vic Wintjes still uses semi-fluid grease in many of the wheel ends in the Canadian Tire fleet.
The maintenance manager began the initial switch from oil because his trailers would sit stagnant for long periods of time. The result was seals that deformed and let oil leak out of the hub.
“With a grease, it doesn’t run out,” he says of the attraction to the product.
With new equipment, however, the fleet is now switching to new components that will solve the lubricant loss and let technicians and drivers stick to traditional oils.
“We feel confident the seal will work,” he says. “With all the new improvements in seal packaging, the method for adjusting proper clearance on the bearings, you’re seeing longer seal life.”
Oils are still better at transferring heat – and that’s especially important in cases were extreme temperatures come into play because of to heavy loads and lateral stresses.
Greases aren’t ideal in every situation, Tanis says. Since wheel ends filled with semi-fluid grease run 30 to 40 Fahrenheit hotter than their oiled counterparts, there could be trouble for those “pushing the envelope”, he says, referring to applications pulling heavy loads or that involve heavy braking.
The temperature change can draw water into the hub, which leads to corrosion problems.
But there are cases in which synthetic lubes are still the best bet, particularly in the way that they’ll maintain their viscosity under most temperature conditions, Wintjes says.
Unlike traditional oils, products like Mobilith 007 won’t turn to molasses in cold weather.
“The grease still has a lot of merit,” he says.
Since running into problems with the application of the grease in 1998, MacKinnon Transport has been spec’ing its wheel ends with a traditional oil, says maintenance manager Brian Burrows, who was working on the shop floor when the problem began to emerge.
But on some leased equipment, the grease is already in the wheel ends. “We jack them up and shake the wheel or pull the cap and make sure (there’s enough),” he says.
To ease inspections, the fleet is also turning to aluminum caps that incorporate a plastic eyeglass to check lubricant levels.
“The only greased hubs that bear looking into are the unitized models. You never take them apart. They’re a sealed unit,” he adds.
“If grease gets on the brakes, it’s equally insidious (as contamination with oil), if not worse,” Tanis adds of another problem that can appear if the grease leaks. “You can’t just wash it off. You have to replace the parts.
“Maybe the mass switch to synthetic, semi-fluid grease is not the great choice it once looked like it was.” n
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