GREASES

IN THIS SECTION, YOU WILL FIND THE FOLLOWING SUBSECTIONS:

GREASE
GREASE CLASSIFICATIONS
MULTIPURPOSE GREASE
CHASSIS LUBRICANTS
WHEEL BEARING LUBRICANTS
UNIVERSAL JOINT LUBRICANTS
GEAR LUBRICANTS
GEAR LUBRICANT CLASSIFICATIONS
REGULAR GEAR LUBRICANTS
EXTREME PRESSURE GEAR LUBRICANTS
MULTIPURPOSE GEAR LUBRICANTS
CHAIN LUBRICANTS
SILICON GREASE

GREASE

Grease is basically a more solid form of oil lubricant. Many forms of grease contain a fibrous content. In addition to providing lubrication, grease must also repel water, protect against corrosion, adhere to the surface being lubricated, and retain its consistency over various operating conditions. The following are some of the most important properties of grease:

–The consistency of a grease refers to its firmness. Consistency is determined by the type and amount of thickener used, the viscosity of the oil, and other factors.
–Grease consistency is measured by a penetrometer. It’s expressed in the depth in millimeters to which the cone of the penetrometer sinks into a sample of the grease under controlled conditions. A lubricating grease is a combination of lubricating oil and thickening agents such as soap fiber. The texture of the grease depends on the types and amounts of thickening agents and lubricating oils combined in the product. The texture is described as buttery, or smooth, when it has no apparent fiber. Grease with short fiber is slightly stringy. A medium fiber grease is somewhat more stringy.
–The fiber of a grease serves to trap the lubricating oil and hold it in suspension. Under a microscope, the various kinds of soap fibers resemble common natural fibers used in textiles.
–Bleeding refers to the partial separation of the oil from the fiber of a grease. Usually, a small amount of bleeding is acceptable.
–The dropping point of a grease refers to the tendency of the grease to melt and leak from the housing or area in which it’s used.
–The dropping point is the lowest temperature at which the first drop of melted grease forms from a given sample under specified test temperature conditions.
–The type of thickening agent in a grease determines to a great extent the suitability of the grease for specific uses. For example, metallic soaps of sodium, calcium, aluminum, and lithium are excellent chassis lubricants because they adhere well to metal.

GREASE CLASSIFICATIONS

Of course, many different kinds of grease are available. The following are some of the more common classifications:

MULTIPURPOSE GREASE

Multipurpose greases usually contain a metallic thickening agent such as lithium soap. They’re manufactured to meet a wide range of requirements, such as the lubrication of chassis bearings, wheel bearings, universal joints, water pumps, and covered springs. Multipurpose greases often contain additives that protect metals against corrosion and oxidation.

CHASSIS LUBRICANTS

Chassis lubricants are of the proper consistency for application with grease guns through grease fittings. They often contain metallic thickening agents. The grease should be resistant to water because the point of chassis lubrication is usually exposed to splashing water and mud.

WHEEL BEARING LUBRICANTS

Wheel bearing lubricants are greases of the proper consistency to provide extended service in antifriction wheel bearings. They usually have short fiber sodium thickening agents. Wheel bearing greases are resistant to high temperatures, but not to the absorption of water. Therefore, greases of this type shouldn’t be exposed to the weather.

UNIVERSAL JOINT LUBRICANTS

A universal joint lubricant is a type of grease prepared exclusively for the lubrication of universal joints. A universal joint is a flexible joint used when up and down movement must be permitted between the power source and the device being powered. This type of joint is most often found between the transmission and rear axles of a rear wheel drive vehicle.

GEAR LUBRICANTS

Gear lubricants have two principal functions. First, they must provide satisfactory lubrication for gears, bearings, synchronizers, sliding shafts of the transmission, axles, and differentials. Second, gear lubricants must act as a coolant for these moving parts. The proper selection of lubricants for use in transmissions, rear axles, transfer cases, and other such parts of the driveline is as important as the selection of an engine oil.

Most of the lubricating oil properties described earlier apply to gear lubricants as well. For example, viscosity is important. Selection of a gear lubricant of the correct viscosity has much to do with ease of gear shifting. It also influences the load carrying capacity of the gears and, to some extent, it affects leakage and gear noise. Gear lubricants, like engine lubricating oil, contain chemical agents for controlling corrosion, wear, and oxidation. In addition, gear lubricants are affected by such factors as channeling point, solid matter content, and foaming.

The channeling point of a gear lubricant is related to the pour point of oil. The pour point is the lowest temperature at which a lubricant will flow. The channeling point is the temperature at which a lubricant is thick enough that when a channel is formed through it, the sides of the channel fail to flow together within a specified time. Normally, the channeling point of a lubricant occurs approximately 15 degrees F below the pour point. It’s important that the channeling point of a gear lubricant be lower than the minimum starting temperature encountered by the equipment.

The solid matter content of a lubricant refers to the solid materials contained in suspension. Such materials are undesirable, as they cause abrasion and wear in transmission and rear axle antifriction bearings.

Gear lubricants shouldn’t foam when agitated. Excessive foaming can result in leakage of the lubricant from the housing to the extent that parts can be damaged from inadequate lubrication.

GEAR LUBRICANT CLASSIFICATIONS

Gear lubricants are classified according to their ability to provide adequate lubrication under specific operating conditions. They’re grouped into four categories: (1) regular gear lubricants, (2) extreme pressure gear lubricants, (3) multipurpose gear lubricants, and (4) chain lubricants.

REGULAR GEAR LUBRICANTS

Regular gear lubricants are straight petroleum oils that are well refined. They’re free from water, sediment, acid, and any other substance harmful to the performance of the lubricant. Some transmission or transaxle manufacturers recommend the use of regular gear lubricants when tooth pressures and temperatures aren’t severe.

Straight mineral oils don’t have extreme pressure characteristics. Therefore, regular lubricants are becoming less and less popular than heavier duty lubricants.

EXTREME PRESSURE GEAR LUBRICANTS

Extreme pressure gear lubricants are for severe service. They’re used in transmissions and spiral bevel gear rear axle assemblies that have a tendency to score (scratch, groove, or mar what should be a smooth surface) and wear when regular type lubricants are used.

MULTIPURPOSE GEAR LUBRICANTS

Multipurpose gear lubricants conform to the requirements of API service classification GL-4. They’re widely used in spiral bevel gear rear axle assemblies and in some worm gear units. Multipurpose gear lubricants are also recommended for most manual transmissions.

The term multipurpose doesn’t mean that a single viscosity grade can be used for all applications under all climate conditions. Multipurpose gear lubricants are available in SAE 80, 90, and 140 grades. The proper grade should be used for the particular application and temperature conditions to which it’s exposed.

CHAIN LUBRICANTS

Chain lubricants are special lubricants that both penetrate and lubricate the rollers, pins, and end shields of common drive chains. They’re specially formulated not only to penetrate but also to stick to these components of the chain. This means the chain lubricants won’t fly off the chain as it moves. Chain lubricants normally come in spray cans that have a tube for directing the lubricant to the chain.

SILICON GREASE

Silicon grease—this lubricant excellent for use with fasteners that have tendency to rust and seize, like those on exhaust systems and coolant components. Silicon grease resists heat. Won’t melt at hot exhaust temperatures and vaporize like engine oil. Silicon grease adheres well to clean metal surface. If surface very clean, grease will never be totally washed away, with soap and water, gas, even solvents. Bolts installed in exhaust manifolds with silicon grease can be removed ten years later.