A vehicle’s drivetrain must resist heat and friction, in all temperatures and circumstances. The forces acting on the gears in a transmission are subject to high loads. The starting a stopping forces transmitted via the transmission from the engine create large amounts of friction and heat on the components. When metal components come into contact, they exert directional loads on one another. Even the smoothest machined surfaces have microscopic irregularities known as asperities. When asperities come into contact, they create wear due to metal-to metal interaction and via flashes of localized high temperature. Lubrication exists to reduce this friction and to dissipate heat. In an ideally lubricated system, the film of lubricant will bear the full load between two surface moving relative to one another.
Transmission fluid additives are especially suited to the forces found in a gearbox. They can be customized for a wide range of conditions, such as temperature extremes or overloading situations. These additives work in conjunction with the base oil or grease in order to improve transmission function and longevity.
Additives commonly found in these lubricants include:
Extreme pressure additives are suited for systems where frequent stopping and starting loads are placed upon the components. Transmissions usually require lubricants with these additives. Some components found in gear systems such as curved-jaw (“Lovejoy”) couplings may not require additional lubrication, but this is because they do not have metal-to-metal surface contact (under normal operation.) For gearbox systems where metal-metal contact is possible and must be avoided, extreme pressure additives offer protection. When high loads are applied, the base lubricant is degraded but the additive remains. These additives, often chlorine, potassium-borate or sulfur-phosphorus compounds, deform to create a last-line barrier between surface contact to maintain operation and prevent wear.
Antioxidant additives and corrosion inhibitors work towards the same end. These help to shield transmission components from the effects of oxygen and oxidizing elements, including moisture. Corrosive forces can include these chemical aspects, but extend to include electrochemical forces found with iron-based (ferrous) metals and alloys of iron. These additives can resist condensation to reduce moisture contamination in a system, resist acid formation and help dissipate heat which would normally speed these harmful processes along.
Bare, non-noble metal will rust over time upon exposure to air, and in mechanical applications there are other oxidizing forces. The addition of heat will speed oxidation and corrosion due to the reactions with acids and bases involved. Anti-corrosion additives work to neutralize these chemicals and protect the longevity of metal components and surfaces. The dynamic forces in a transmission require the right care, the right lubrication and proper maintenance to function properly.
As stated, the right fluids and greases are vital to the operation of a transmission’s many moving parts. Knowing the correct viscosity, additives, and base oil is essential to maintenance of a geared system. The wrong viscosity can create metal-to-metal contact if too thin, and create drag and power loss if too thick. Over lubrication can cause seal damage and failure, and under lubrication can lead to seizure and catastrophic failure of a transmission.
Ensuring that your transmission components are serviced regularly by a certified professional is key to longevity. Transmission rebuilds must also be managed by experienced professionals. For more information, you can view High Gear Transmission’s online transmission fluid guide. Feel free to contact us with any additional questions regarding your transmission or gearbox components today.