Meyers Transport's Al Thompson is confident that 2,000 wheel ends will never spill a drop of oil under his watch. It's quite a claim, really, given the prevalence of leaking wheel seals throughout the trucking industry, but he can take the stance...
Meyers Transport’s Al Thompson is confident that 2,000 wheel ends will never spill a drop of oil under his watch. It’s quite a claim, really, given the prevalence of leaking wheel seals throughout the trucking industry, but he can take the stance because soon his fleet won’t be using oil.
Each of his wheel ends will be lubricated with National Lubricating Grease Institute (NLGI) No. 2 grease.
The maintenance director in Belleville, Ont. is coy about the number of leaking seals that led to the decision to use the thicker lubricant, saying only that it was “more than we would have liked to see.”
But Glenn McKinnon, service manager for Muskoka Transport, suggests that as many as 10% of oil seals will fail prematurely. “You would hope they’d go from brake reline to brake reline,” he says. “We all know [they won’t].”
Once a seal fails, it can take as long as two hours to service oil-soaked brake linings, McKinnon adds, referring to the related maintenance costs that his Bracebridge, Ont. fleet hopes to avoid as it switches to grease-protected wheel ends.
That’s the best-case scenario. If a leak isn’t detected, an oil-starved bearing can lead to a “catastrophic failure” that’s known more simply as the loss of a wheel.
A LONG HISTORY
As unusual as the shift to grease may sound, the lubricant is already used in European wheel ends, and was even common in North American components until a few decades ago.
The use of oil didn’t even begin until 1951, following a casual conversation between Stemco sales manager Tom Davidson and a mechanic who wondered why bearings had to be lubricated with grease. After all, grease-covered bearings made work on the era’s inboard brake designs a messy proposition; oil could simply be drained out of the way.
Stemco engineer Tom Arnold took the question as a challenge, developing the industry’s first oil seal and hub cap.
It didn’t take long for maintenance managers to embrace the designs. A mere 5% of US fleets were using oil seals in 1955, Stemco says. By 1960, almost one in three wheel ends had oil seals, and that share grew to 90% by 1979.
Ironically, the lubricant’s use continued to grow throughout the 1980s, even as the trucking industry began to embrace hub-pilot wheels with outboard brakes that could be serviced without draining the oil.
The maker of wheel components suggests that 95% of North America’s heavy trucks now use oil seals, indicating wheel ends lubricated with oil or a semi-fluid grease.
STICKS WITH IT
But a wheel end will lose its supply of oil if the seal isn’t properly installed or is pushed out of position.
Oil seals also wear due to pressure build up if the vent is plugged or not working, explains Timken sales engineer Bill Ratcliff.
Some leaking oil seals could be addressed through better installation practices, suggests Todd Anderson, Stemco’s vice-president of engineering. Approved tools ensure the force from a hammer or hydraulic press is applied in the proper position. A 2×4 – a common tool in many shops – doesn’t offer the same level of control. “That can deform the seal.”
He even takes the unusual stance of suggesting there is a positive aspect to leaks.
“It can be an indication of another problem in the wheel end,” Anderson explains. “Let’s say the bearing is set too tight and running hot. With a No. 2 grease, you can have a bunch of problems [like that], and your wheel end looks fine. You don’t have the flag saying, ‘Hey, look at me!’
“Your failure mode can be more catastrophic, where a problem doesn’t get addressed until you see your wheel passing you on the highway.”
Still, a number of fleets have decided that grease is the best solution. So far, at least 30 Canadian carriers are testing Timken’s grease-protected Wheel Boss wheel ends, and nine have chosen the systems as their standard spec’s.
One of the primary advantages to using NLGI No. 2 is that the lubricant will stay where it’s put. Ratcliff, for example, illustrates the point by grabbing a small canister of the grease and dropping the open end on a table to show how nothing will flow out of the container. It sticks in place like peanut butter in a jar.
But there is a debate surrounding other lubricating properties.
Anderson insists that oil-protected bearings are flushed clean whenever they splash through their pool of lubricant at the bottom of each rotation. “With No. 2 grease, there’s no motivation for the contamination to leave,” he says, referring to the grease that is packed in place. “Whether it’s moisture or grit, or even metal shavings or particles, oil can pull those away from the bearing.”
Problems with grease-packed components can occur more quickly than those associated with wheel ends that are protected by oil, Anderson adds. A metal surface that isn’t properly coated with grease during an assembly process, for example, will quickly be exposed to the condensation that can lead to rust.
Oil is also a better choice for pulling heat away from a bearing, he says.
But Ratcliff doesn’t accept this common refrain from those who support oil. “There isn’t a wheel in the world that goes fast enough to require oil,” he says, adding that the argument is only true for high-speed machine spindles. “That is where the old saying ‘oil runs cooler’ comes from.”
He points to race cars as proof of his assertion, and questions why those wheels are lubricated with grease, even though they easily outpace any trucks on the road.
Ultimately, there are advantages and disadvantages with any type of lubrication, Anderson says. Stemco, for example, sells seals for grease or oil users. “We have seen both of them work in wheel end settings in different applications.”
Customers, after all, will have the final word on grease.