Grease has been around for thousands of years. The name springs from a Latin word for fat, which ancients used to keep wagon wheels rolling. But while the technology has certainly improved, we still use grease.
Why? Think of grease as a sponge that holds oil and gradually releases it. That makes it useful where frequent relubrication is inconvenient. Also, grease can seal and protect components from moisture and contaminants. The principal virtue of grease – the fact that it stays put – is also a limitation. You can’t expect grease to perform the cooling and cleansing functions normally associated with oils. But, in the right applications, it’s the perfect solution.
What to use where
OEMs publish ratings a grease must meet to be acceptable for use on their vehicles at various lubrication points. However, these are minimum scores. Just because a grease meets them doesn’t necessarily mean it’s the best choice.
Stocking, and training technicians to use, several different kinds of grease, has its benefits. “There are advantages to using different greases in different vehicle areas,” says Dan Arcy, product marketing manager for Shell Lubricants. “For example, a tacky grease that won’t easily wash off a fifth wheel isn’t as good in high-speed applications, like U-joints.”
What about wheel bearings? Because they endure wide variations in speed and temperature, greases with good mechanical and high-temperature stability, designated NLGI GC, are desired. Normally, a smooth, lithium-based product works well, because it has good ‘slumpability,’ or ability to adequately penetrate rollers, races and cages.
Of course, most heavy-duty vehicles use an oil-filled hub to lubricate bearings and, according to the Technology & Maintenance Council, this is the preferred method, as it makes for somewhat cooler running temperatures.
However, some fleets that have had problems with leaky wheel seals have turned to mineral-based or synthetic semi-fluid grease for wheel bearings, since it won’t get past a damaged or improperly installed seal and contaminated brake linings.
