How to understand grease differences

Restoring an antique tractor often leads to encounters with grease that has hardened. Before you finish the job, you’ll have to decide what type of grease should replace it.

Grease basically serves two purposes: It provides lubrication to the bearing or metal-on-metal joint to reduce friction and wear, and it drives away moisture and helps seal out new moisture. The latter is more important for antique equipment than the former.

If a tractor is driven only a few times a year in a tractor parade, the parts and bearings aren’t going to see a lot of wear, but they do need to be protected from moisture and rust.

Heavy oil in suspension

In general, grease is simply heavy oil with an additive (most often soap)to make it thick enough to stay in place. Hence, grease is used when an oil lubricant would leak or would not properly seal the lubricated part.

It’s also formulated to gradually release the lubricant it contains. As grease liquefies, it delivers a lubricating oil and also the additives in it.

Historically, the first grease was animal fat used to lubricate the axles on chariots and wagons. Now, grease has turned into a multifaceted lubricant able toperform under a wide variety of uses for tractors, trucks, and complex equipment.

Grease composition

Grease is mostly comprised of base fluid (75%to 95%) typically composed of Group I and Group II mineral oil-base stocks. That’s followed by thickener (5% to 25%)and additives (0% to 15%),which provide most of the unique features of the grease and enhance its performance. A number of additives are similar tot hose used in engine and hydraulic oils, including oxidation inhibitors, corrosion inhibitors, anti-foam agents, rust inhibitors, and anti-wear compounds.

Other popular additives are molybdenum disulfide (moly) and graphite, which reduce friction by filling in the small voids in the surface of bearings. Moly also gives extreme-pressure (EP) greases their ability to stand up under intense loads.

Another additive in some grease is a tackifier, which gives grease a tacky feel and helps keep it in place. Finally, dye can be added for easy identification by the enduser, even though the color does not necessarily indicate a particular application. Common colors are red, green, and blue.In many cases, red pigment is used to identify extreme use and/or high temperature use, but that is not the case among all manufacturers.

NLGI (formerly the National Lubricating Grease Institute) administers standards for grading greases. In one test, the hardness or softness of grease is rated by dropping a cone into a grease sample. The depth of penetration in five seconds is then measured and converted to one of nine NLGI grades from 000 to 6. The higher the grade number, the harder and stiffer the grease. Lower-grade numbers signify softer, more fluid grease.

Another NLGI test determines the grease’s dropping point, or the temperature at which a grease passes from a semisolid to a liquid. This dropping point, which can vary between 200°and 500°F, changes with different formulations.

To measure the dropping point, technicians apply grease to the wall of a test cup and place it in a special oven along with a thermometer that measures the temperature in the cup without touching
the grease or the sides of the cup. The dropping point is the temperature at which one drop of oil falls from the cup wall.

Regardless of what grease formulation you select, always clean off the zerks before adding grease. If you apply grease before cleaning off the fittings, you push any dirt that has collected on the zerk into the bushing or bearing, where the dirt will act as an abrasive and could lead to premature failure.

Picking the right grease for your tractor

Which type of grease is best for antique tractors? General-purpose grease is designed to work in a variety of applications, but that doesn’t mean it is not specific. Some general-purpose greases are made for specific vehicle brands. Consequently, multi-purpose grease is the most commonly used formulation where heat is not an issue.

Grease distributors will offer high-temperature grease, marine grease, anti-seize grease, moly grease, and other specialty formulations. However, these likely will never be needed in a tractor restoration. They most likely didn’t exist when your vintage tractor was built.

The exception for current use might be assembly grease, which sticks to the metal components and protects the parts from rust and moisture during a rebuild. Some grease formulations pro-vide better cling to metals and better resistance to both water washout and spray. These can be useful on chain drives and other applications in which resistance to spin-off is needed.

Avoid mixing different brands and formulations of grease. When greases made from different thickeners are mixed, the result may offer poorer in-service performance or physical properties than either of the component products alone. This lessening in performance capability may show up in any of several areas, such as lower heat resistance, change in consistency (usually softening), or decrease in shear stability.

Remove all old grease

Ideally, the best procedure to follow when changing grease brands is to completely remove all old grease before new grease is added. This is usually done, for example, when wheel bearing sare repacked with grease.But any complete restoration usually involves removing as much grease as possible, as well.

During a change from one grease type to another, when complete removal of the old grease is impractical, much of the old grease may be removed by purging with new grease. This can be done initially and/or progressively by temporarily increasing the quantity of grease applied and shortening the application interval.

The bottom line is that more frequent grease application may be the best bet anyway. Several tractor restorers have commented that lubrication frequency with antique equipment is more important than grease formulation. Because restored antiques often sit for long periods, a fresh application of grease is a good way to purge any accumulated moisture and debris. Just keep an old rag handy.