What do the transmission oil classifications API GL-4 and GL-5 mean?
The API classification for transmission oil defines the anti-wear properties of the oil. The higher the number the more efficient the additives against wear. Oils in the highest GL-5 class are normally used in the so-called hypoid drive gears in the rear axle of rear-driven vehicles, which need as efficient additives as possible. GL-4 oils have less additives and are normally used for the transmission of front-wheel drives. The API class has to be selected according to the vehicle manufacturer’s instructions. Using too small a class may result in more rapid wear of parts, whereas using too large a class may cause poor synchronisation in manual transmission.
