Over-the-road and off-road equipment transmission and differential components are exposed to higher pressures and speeds. It is critical that the gear lube chosen must be engineered to withstand extreme heat, be able to control contamination and deposits, have the ability to withstand extreme pressure and shock loads, be compatible with all seal materials, have the capacity to extend seal life, and should have the proper additive package to meet a broad range of OEM specifications such as Limited Slip, API MT-1, Rockwell, and Mack GO-J.
Modern over-the-road and off-road heavy equipment and vehicles are being designed with advanced aerodynamic bodies and shapes to improve air flow and improve fuel economy. This new aerodynamic design strategy comes at a cost when the discussion of cooling critical power train systems arises. Less cooling translates to higher operating temperatures for transmissions and differentials. Also, when outside temperatures are higher, travel speeds are slower, and loads are heavier, choosing the right gear oil is important if the transmissions and differentials are expected to be properly protected over long periods of time. When considering which is the best gear oil for a differential, it is a good idea to check an oil’s minimum flash and fire point. A quality gear oil should have a minimum flash point of 400 degrees Fahrenheit and a fire point of 440 degrees Fahrenheit. Most ordinary gear oils would not be able to protect components at high temperatures, so one needs to look at custom blended or specialty gear oils that can handle temperatures of 100 degrees Fahrenheit higher for short durations. In terms of what type of base oil should be looked at, the bare minimum would be a 95 VI paraffin base stock oil. These oils are considered “neutral” oils. They have been highly refined with almost all impurities extracted. What this means is these types of high VI base stocks will not thin out when exposed to high temperatures, nor will they increase viscosity when outside temperatures are cold. Because they are 98% pure, they will not form sludge, varnish, and other contaminants as other lesser quality base stocks would. Of course, beyond looking for a gear oil with a minimum 95 VI, the additive package is just as important. In the case of differentials, the additive package is quite critical. It would require higher amounts of EP agents, friction modifiers, anti-foam agents, anti-wear agents, and rust and corrosion inhibitors. The additive system must be able to help eliminate any chatter experienced in limited slip differentials. Such a gear oil would be perfect for limited slip differentials such as Twin-Grip, Track-Loc, Traction-Lok, Sure-Grip, and others.
Another factor to look at when choosing the best gear oil for a differential is to check whether the gear oil has been tested utilizing the extreme pressure industry test called the Timken OK Load Test. The higher the number, the better the gear oil’s ability to withstand extreme pressure and shock loads. A score of 70 or more should be a minimum rating if the expectation is for the gear oil to protect critical components during extreme operating conditions over long periods of time. To reach these kinds of ratings of 70 plus on the Timken OK Load Test, the oil must possess superior extreme pressure additives at higher volume. If the gear oil has the proper EP additive chemistry, it should provide protection against gear surface fatigue, which can be called spalling. Also, it should be able to reduce wear metals such as iron.
Conventional brand name gear oils, though well known, have been found to score lower on many industry standard testing when the competition involves specialty or custom blended lubricants. Beyond testing, actual visual results when transmissions and differentials have been disassembled tend to show much more sludge and gum deposits when compared to specialty gear lubes. Apparently, custom blended gear oils follow a different philosophy. They are designed to meet performance standards rather than price standards. It could be stated that brand name lubricants seemingly are formulated by accountants rather than by chemists. The competition for sales is so high among major brand lubricants that price seems to be paramount rather than performance. It is with this idea that it may benefit the smart owner/operator to keep an open mind when looking at custom blended gear oils. On the surface, they may seem much higher in initial price, but long term they offer potentially substantial savings, not only in protecting critical components, but also adding profits to the bottom line. Back to the subject of sludge and gum deposits, which typically are caused due to extended high temperature exposure. Lesser oils can’t take the heat. If your equipment is operating under extended high temperature conditions, then most likely the only choice to consider would be a specialty gear oil. To combat and prevent sludge and gum deposits, a custom blended gear oil typically utilizes state-of-the-art additive technology designed to minimize deposits and sludge. Please be aware that many transmissions and final drives are being forced to operate at much higher temperatures that can range from 280 degrees Fahrenheit all the way up to 320 degrees Fahrenheit. With these higher temperatures, an increase in transmission synchronizer coking has become more and more prevalent. Transmission synchronizer coking causes difficulty in gear changing. The culprit is deposit formation due to an inadequate gear oil being utilized. Simply choosing a gear oil that can withstand much higher temperatures and that utilizes the proper additive technology that prevents sludge and gum deposits, the shifting problems can be a thing of the past. Also, if deposits are eliminated, then the gear oil is able to flow to critical bearings and gears without dealing with unnecessary obstructions caused by deposits formed by oil, passageways, and filters.
A reoccurring theme in this article and in every day equipment operation is the issue of dealing with high temperatures. One area of transmissions and differentials that are temperature sensitive are the all important and critical seals. If temperatures remain high and unchecked, seals can be damaged to the point where they degrade and start to cause premature oil leakage and deposit formations. Industry tests have shown that temperatures in and around the seal area typically operate within a range of 30 degrees Fahrenheit to 50 degrees Fahrenheit beyond sump temperatures. These higher temperatures, if not brought under control, will cause deposits to form around the seals, leading to elastomer losses. If the seal loses its elasticity, then one can expect oil to start leaking. Look for a high performance gear oil that offers a chemistry and base oil that can withstand very high temperatures while being compatible with all seal materials. By choosing the best gear oil for a differential, high temperatures should fall to normal operating conditions. By lowering temperatures a multitude of problems are solved, one of them being extended seal life.
To recap, look for a high quality heavy duty gear lubricant formulated for limited slip differentials utilizing 95 VI base stock oils, a robust and superior additive chemistry that can hold up under extreme pressure, withstand higher than normal temperatures, and control damaging sludge and deposits.