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Gear Oils for Manual Transmissions

Automotive gear lubricants, similar to engine oils, are classified by the API in terms of the performance required by a particular application. As in the case of engine oils, these classifications do not define or reflect oil viscosity. To completely specify a gear lubricant, both the API service designation and the SAE viscosity grade are required. Axle and transmission lubricant viscosities are defined separately in SAE J306 recommended practice. Multigrade lubricants are normally used and each viscosity grade has distinct criteria for low and high-temperature performance.

SAE Viscosityclass acc. to SAE J306

SAE- class Min. temperature at dynamic viscosity Kinematic viscosity at 100°C, mm2 / s
  150 Pa*s, °C Min Max
70W -55 4.1 -
75W -40 4.1 -
80W -26 7.0 -
85W -12 11.0 -
90 - 13.5 24.0
140 - 24.0 41.0
250 - 41.0 -


Requirements for Gear Oil:

  • Lubrication, shear stability of the lubricant, reliable wear protection for transmission components and gaskets, antifoaming, temperature control, corrosion protection, load carrying capacity, prevention of pitting, dispersing power, insensitivity to seals, insensitivity to metals, miscibility with other lubricants.
  • Switching and synchronization behaviour.
  • Prevention of noise while idling and operation, low noise operation at high and low temperatures, speeds and loads.
  • A means of extending service intervals of increasing demands on the lubricants, the oils, i.e. consistent functionality over the duration of use, high thermal and oxidative stability for long applicability and optimal conditions for reducing friction energy losses.
  • Cold start. Wear-free starting behaviour at low temperatures.

In addition to the factory standards of the relevant motor vehicle industry, the guidelines for gear oils with the American Petroleum Institute (API) are relevant. However, the API classifications can only provide a rough classification, as the requirements are very complex to modern gear oils.

GL-1 Inactive 1)
Designates the type of service characteristic of manual transmissions operating under such mild conditions of low unit pressures and minimum sliding velocities, that untreated oil may be used satisfactorily. Oxidation and rust inhibitors, defoamers and pour depressants may be used to improve the characteristics of lubricants intended for this service. Friction modifiers and extreme pressure additives shall not be used.
GL-2 Inactive 1)
Designates the type of service characteristic of automotive type worm-gear axles operating under such conditions of load, temperature and sliding velocities, that lubricants satisfactory for API GL-1 service will not suffice.
GL-3 Inactive 1)
Designates the type of service characteristic of manual transmissions and spiral-bevel axles operating under mild to moderate to severe conditions of speed and load. These service conditions require a lubricant having load-carrying capacities greater than those that will satisfy APL GL-1 service, but below the requirements of lubricants satisfying the API GL-4 service.
GL-4 Designates the type of service characteristic of spiral-bevel and hypoid gears in automotive axles operated under moderate speeds and loads. These oils may be used in selected manual transmission and transaxle applications.
Gl-5 Designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and / or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.
GL-6 Inactive 1)
Designates the type of service characteristic of gears designed with a very high pinion offset. Such designs typically require (gear) score protection in excess of that provided by API GL-5 gear oils. The original API GL-6 test equipment is obsolete.
MT-1 Designates lubricants intended for non-synchronized manual transmissions used in buses and heavy-duty trucks. Lubricants meeting API MT-1 provide protection against the combination of thermal degradation, component wear, and oil seal deterioration which is not provided by lubricants meeting only the requirements of API GL-4 and API GL-5.
1) API Categories GL-1, GL-2, GL-3 and GL-6 were declared inactive by SAE Technical Committee 3 in 1995, even though oils may be marketed with these designations. Similarly, ASTM does not plan to maintain the performance tests associated with these categories, as in a number of cases these tests can no longer be run because parts or test installations are not available.

To ensure the function of the transmission over the entire duration of use requires special gear for the respective assemblies. So gear oils today are included as a design element in the development.