The concept of "maintenance instead of repair" has been widely accepted by many truck owners. However, truck maintenance is not an easy task. Just the regular replacement of various oils alone can be quite a headache. In the previous episodes, we have already introduced engine oil. Today, 
this episode of accessory knowledge will introduce gear oil and related maintenance issues.
Gear oil is also known as tail gear oil. It is mainly composed of petroleum lubricating base oil or synthetic lubricating oil, and is formulated by adding extreme pressure anti-wear agents and oiliness agents. It is an important type of lubricant, mainly used in various gear transmission devices, such as transmissions and drive axles.
Gear oil is mainly used to lubricate various gear components. It can help dissipate heat in the machinery during vehicle operation, reduce gear wear, extend the lifespan of gears, prevent rusting of gears, and improve transmission efficiency, etc.
As an important part of power transmission, the gear end faces of the gearbox and the drive rear axle are subjected to extremely high pressure. Once the oil film of the gear oil is broken, the gear end faces will directly come into contact. Under the pressure of high torque, it is very likely to cause damage to the gears, thereby leading to problems such as shaking and abnormal noises in the drive axle.
The replacement cycle for gear oil is generally around 60,000 kilometers. Before reaching the expiration date, it is necessary to replace it in time. Just like engine oil, gear oil also has its own classification.
Internationally, the performance classification of APL (American Petroleum Institute) is generally used. Gear oil is classified into five basic types: GL-1, GL-2, GL-3, GL-4, and GL-5.
API vehicle gear oil quality grades
· GL-1 mineral oil without additives
· GL-2 mild extreme pressure for turbines
· GL-3 mild extreme pressure for rear axles and gearboxes, suitable for spur and helical gears structures
· GL-4 medium extreme pressure, medium strength for double-curved gears and manual gearboxes, equivalent to MIL-L2105
· GL-5 high extreme pressure, suitable for all double-curved rear axles and some manual gearboxes, equivalent to MIL-L2105D
In China, vehicle gear oil is mainly classified into three grades based on its performance:
L-CLC: It is made by refining mineral oil and adding antioxidants, rust inhibitors, anti-bubble agents and a small amount of extreme pressure agents. It is suitable for manual transmission boxes of medium-speed vehicles and drive axles with relatively demanding load conditions featuring curved tooth bevel gears.
L-CLD: This is a refined mineral oil that is processed with antioxidants, rust inhibitors, anti-foaming agents, and extreme pressure agents, etc. It is suitable for various gears operating under low speed and high torque or high speed and low torque conditions, especially for quasi-conical gears used in buses and other vehicles.
L-CLE: It is made from refined mineral oil, along with antioxidants, rust inhibitors, anti-foaming agents, and a large amount of extreme pressure 
agents. It is suitable for various gears operating under high-speed impact loads, high-speed low-torque, and low-speed high-torque conditions, especially for quasi-conical gears in buses, trucks, and other vehicles.
The content of extreme pressure agents in these three grades of gear oil gradually increases. For vehicles with high power and large torque like trucks, the L-CLE grade of gear oil is the best choice.
Of course, this is just a simple classification. When choosing, it is necessary to consider the overall situation from both the vehicle type and the working environment. For light trucks and medium trucks, the load-bearing capacity is relatively low, and the load on the gears is not particularly heavy. Therefore, the requirement for the extreme pressure and wear resistance of the gear oil is relatively low. However, for heavy trucks, which have long transportation distances and heavy loads on the gears, gear oil of GL-4 or higher grades must be used.
