Slippery Situations
When it comes to grease and preventive maintenance, we've got a brand new problem. Two of today's biggest maintenance concerns – preventing corrosion and extending maintenance intervals – are at odds with each other.
Deborah Lockridge
Senior Editor
Here's the rub: Many fleets have been extending oil drain intervals out beyond equipment manufacturers' recommendations, using oil analysis to ensure that the oils are still doing their job. But some fleets forget that they need to coordinate their greasing efforts with these extended drains. Your average grease won't stand up to those long drain intervals, and you can't analyze it as easily as your engine oil to make sure it's still doing the job.
So choosing the right grease and applying it properly are vital to achieving the goals of corrosion prevention and extended PMs.
Grease manufacturers admit that not much research has been done about the effect on grease of new, more corrosive de-icers being used by many states, such as magnesium chloride and calcium chloride. The basic principles of corrosion prevention should not only still apply, but be more important than ever to prevent the corrosive-chemical-laden water from finding its way into your chassis components.
Grease prevents corrosion in two ways: It acts as a physical barrier to water, and it contains additives that chemically work to prevent corrosion. After a period of time, the physical barrier gets worn down, and the chemicals lose their effectiveness. Greasing is needed at regular intervals to maintain the protective properties.
Chassis components, by their very nature, make it hard to keep lubrication in place.
"The constant pressures that are applied to the driveline and the chassis eventually work grease out of the component," says Mark Betner, heavy duty product manager at Citgo. "When you work that grease out, you allow contaminants to intrude, or enter, that component."
Stede Granger, OEM technical manager for Shell Lubricants, explains it this way. "Some of these joints that require grease are types of joints that have movement that really minimizes the internal relubrication effect. Some of these joints, like the spring pin joints or some of the tie rod end joints, have a tendency to push the grease away from the point of contact."
Add the trend toward extending maintenance intervals, and that can become a problem.
"We're seeing extended drain intervals; we're seeing engine oils that don't have any problem running 50,000 miles," says Bryant Hardy, a principal scientist at ConocoPhillips Lubricants. "Even though the engine oils can live out that long, other components along the driveline that are lubricated with grease can't."
You have several options: You can bring the truck into the shop between oil drain intervals for a secondary PM appointment where it is greased; you can outfit your equipment with automatic chassis lubrication systems; or you can find a premium grease that can stand up to the longer oil drain intervals.
The Right Grease
Choosing the right grease is a bit more difficult than picking an oil. Unlike engine oil, there aren't classifications such as the CJ-4 type ratings you see in the API "donut."
The first thing to do is look at what the equipment manufacturer recommends, says Douglas Pond, commercial vehicle lubricants adviser for ExxonMobil. Then you can build from there, depending on your specific needs. "If it's a matter of extending oil drain intervals, you need to pick a grease that's going to stand up to that. You're going to look for things such as oxidation resistance, resistance to thermal degradation, structural stability while in application, temperature range and corrosive resistance."
One place to start is the National Lubricating Grease Institute's service classifications. ASTM D 4950 is a standard for automotive service greases, with chassis lubricants designated by the letter "L" prefix, and wheel bearing lubricants indicated by the letter "G" prefix. The two highest performance levels are GC and LB; the combination GC-LB represents a multi-purpose category.
NLGI also sets standards for the fluidness of grease. For instance, an NLGI No. 2 grade grease is typically what's used for greasing chassis, while automatic chassis lubrication systems may use a more fluid grade such as 0 or 00.
You need to make sure you're using a grease designed for heavy-duty truck applications, not for regular automotive use, Betner says.
"Grease is basically made up of three components: base oil, thickener and additives. All three components need to be optimized for ultimate performance in a truck fleet chassis. One of the significant areas lacking in many greases is the base oil viscosity selection. A true high-performance, heavy-duty truck grease should have a much heavier base oil component than greases used for general purpose. This offers significant improvement in prevention of water wash-out from highway spray and significant improvement in the staying power of the grease, especially when extended service intervals are needed."
At the same time, don't be tempted to go too far in the other direction, says Shell's Granger. "Sometimes people think the heavier it is, the better it is." But a grease that's too thick won't have the pumpability needed to get into tight areas on a truck, he says – places like the U-joint.
"The very important thing about greasing the U-joint is you have grease that gets into all four cups of the U-joint. If you pick a grease that's more designed for, say, construction equipment, it doesn't pump easily enough to get all four of those cups lubricated the way you should."
In addition, he says, "If you look inside a U-joint, the bearing point is a thin needle bearing, and those must be free to rotate. You don't want to put a heavy, sticky grease in on all those little needle bearings."
If you're concerned about corrosion protection, there are a couple of things you can look for. First, does the grease pass the ASTM D 5969 corrosion test? "Many greases fail to pass this test," Betner says. "Failure to pass this test would certainly raise the question of how much corrosion protection there would be for chassis components when exposed to corrosive chemical contaminated road water."
ExxonMobil's Pond also suggests another test, ASTM 6138, also called the Emcor bearing test. "It subjects bearings lubricated with grease to extreme wet, corrosive environments and measures the amount of corrosion on bearing surfaces," he says. Not all manufacturers will have that information, he says, but if they're touting the ability of a particular grease to resist corrosion, they should.
Another thing to consider is the type of thickener used, such as lithium complex, aluminum complex or calcium sulfanate. Greases with different types of thickeners may be incompatible with each other. When that happens, they may not work right, and you'll end up with excessive wear.
Several companies market "extreme" truck greases designed for tougher applications, such as extended maintenance intervals, and these also typically have excellent corrosion protection, because they're designed not to wash out as easily. Synthetic greases are another option.
Grease Myths
Because choosing the right grease can be complex, many trucking customers (and even lubrication salespeople) have adopted ways of evaluating grease that don't really tell you anything.
"Don't get stuck on tacky appearance, color, high-temperature claims or attempt to evaluate grease by squeezing a small amount between your fingers or doing the palm/water test believing that these types of things truly are performance indicators of fighting corrosion, water wash-out or staying power in the chassis components," says Citgo's Betner.
"There's a lot of what I call eyeball lubrication testing going on," Betner says. "Grease has lent itself to that because it's designed to stay put, so there's more opportunity to touch it and mess with it (than there is with oil). Unfortunately, what looks good to the eyeball may not prove out in real world truck service."
For instance, ConocoPhillips' Hardy wants to debunk the "hammer test," where you put a drop of grease on a plate and hit it with a hammer. "They think that shows them how well grease will stay put," he says. It doesn't.
One of the most common and most useless guidelines used to evaluate grease is the color. Lubrication engineers say some people insist that a certain color of grease is better, but color has no effect on the grease's performance.
"If we change the color of a grease, we will instantly have a dozen complaints," says Hardy. "Color's important, because it helps you see new grease when you're trying to purge grease out of a bearing. But other than that, it makes no difference."
John Geyer, industrial marketing specialist for Chevron Global Lubricants, says some customers will just refuse to use a grease that's a different color than what they're used to using. "Even if the grease has far better properties than their current product, they'll often ask, 'Can you make it in this color?' "
Another myth, says Pond, is the idea that more moly is better. Research has shown that a small amount of molybdenum disulfide, known as moly, improves the performance of grease.
"Moly is what I call that last-ditch effort," he explains. "when everything else is gone, the moly is that last soldier standing if you're in extreme conditions or if you haven't greased the thing in who knows how long." However, he says, "when we do comparisons, we found no difference in performance between higher amounts of moly and lower amounts of moly."
Because moly is becoming a very rare substance in the world, he says, the difference between 1 percent moly and 2 percent moly "increases the cost enough to make your eyes open."
The ultimate indicator of whether you've got the right grease is its performance in your trucks. "The acid test it to put them in your truck and see if they survive a certain period of time," Betner says. "Are your components lasting longer, or are you still having problems, even if you've applied good maintenance practices?"
Of course, choosing the right grease is only part of the battle. It needs to be reapplied properly and at regular intervals. The best grease in the world won't do any good if it's not where it's supposed to be.
As Geyer says, "The common lubrication still applies: The right product, in the right amount, at the right time will prevent 90 percent of your grease problems."
Maintenance for Profit continued...
