Specification for transmission oils API (American Petroleum Institute)
1) GL-1 - oil without additives.
2) GL-4 - oil enriched with EP additives.
3) GL-5 - oil enriched with high levels of EP additives. Suitable for heavy duty and heavy duty applications. Suitable for hypoid axes.
4) MT-1 - an oil designed specifically for mechanical transmissions.
The SAE (Society of Automotie Engineers) classification of transmission oils indicates the grade of oil viscosity.
The SAE for transmission oils is different from the SAE for engine oils. Transmission oils have higher rates.
Some vehicle manufacturers recommend using engine oil for transmissions that is sufficiently enriched with the necessary additives.