Volume 2 Issue 2 - Extra

In this issue of Lube Notes, I will respond to the numerous questions I receive from month to month about gear lubes. From the questions I receive, I realize that folks are not really sure what gear lubes are or exactly why they are different from motor oils. I want to briefly introduce gear lubes and discuss their classification system. Then we will look at proper applications for gear lubes.

First, a little knowledge of gears is important in order to understand the function of gear lubes (please refer to Figure One on the next page for this discussion). Gears transmit motion and power from one rotating shaft to another rotating shaft providing multiple applications of power transmission. There are several types and various geometric shapes for gears but I will only address automotive applications. In Figure One, spur gears, bevel gears and hypoid gears are displayed; sun and planetary gears will be discussed with automatic transmission systems. Spur gears are simple gears with easily meshing gear teeth that transfer power between parallel shafts. Bevel gears allow intersecting shafts to transmit power. Hypoid gears facilitate the transfer of power between non-intersecting shafts at right angles. The important concept to grasp in these gear sets is the action of contact and sliding motion. The spur and bevel gears are engaging and rolling in motion whereas the pinion and ring in the hypoid gears are contacting and sliding. This sliding action allows the Hypoid gears to transmit greater power (the force is distributed over the sliding area), providing for smaller differentials in auto and truck applications.

Design and Function of Petroleum/Synthetic Gear Oil

With this summary introduction to gears, we can now go forward with the design and function of gear lubes. Gear lubes must achieve the following:

• Provide for proper shifting in manual transmissions at all temperatures
• Maintain fluid separation of moving metal surfaces
• Reduce friction and wear
• Lubricate associated bearings
• Prevent scoring of highly stressed gears
• Provide fluid flow in cold temperatures
• Remove heat during operation to maintain safe temperatures
• Demulsify (separate from water)
• Prevent Rust and Corrosion
• Resist foaming and dissipate entrained air bubbles
• Be compatible with all seals

Gear lube is a complex product accomplishing a multitude of functions and if any of these functions are ignored it can result in damage to the components.