Just as modern motor oils are out of place in classic cars, modern gearbox oils only belong in modern vehicles. This is because new oils are generally too low viscosity for old gearboxes. The material compatibility also plays a major role: For in many classic car gearboxes, particularly if built before 1950, non-ferrous metals, such as bronze as well as white metals or alloys, were still used. They cannot tolerate the additives in modern gearbox oils. “They attack the metals. Also, the additives in the API classes GL 5 and 4 are simply oversized for classic cars,” says Oliver Kuhn. He is the assistant laboratory manager for lubricants at LIQUI MOLY.
The classification of gearbox oils touches upon the American Petroleum Institute (API) and ranges from API GL 1 to API GL 5. Put simply: The higher the number, the more modern the oil is and, correspondingly, the greater the additives are. “Manual gearboxes and axle drives used to be separated and, consequently, the properties for the respective gearbox oil were also clearly defined,” explains Oliver Kuhn. Manual gearbox oils were designed predominantly for their behavior towards the synchronizer rings and were given fewer or milder additives. Because there are significantly higher pressures in axle drives, the lubricants correspondingly had greater additives.
One might therefore assume that old lubricant oil recipes could be used. But the expert advises against this: “These do not correspond to the latest level of knowledge. In turn, they do not have sufficient additives,” explains the expert. The LIQUI MOLY Classic gearbox oils SAE 90 and SAE 140 fill this niche with specially adapted additive packages. “Our new gearbox lubricants combine the latest expertise with the understanding for the requirements of old vehicles.”
As classic cars are almost exclusively used in summer, both gearbox oils are a little thicker and the base oils are adapted to the age of the vehicles.
While the Classic gearbox oil SAE 140 is suitable for manual gearboxes of classic vehicles and axle drives with low loads, the SAE 90 can only be used in manual gearboxes. LIQUI MOLY recommends both lubricants for vehicles, motors and transmissions requiring the following specifications or genuine part numbers: API GL1, API GL 2, API GL 3. Both Classic lubricants are available in 1 litre containers.