API classifies automotive gear lubricants in terms of 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 as shown below. Multi-grade lubricants are normally used and each viscosity grade has distinct criteria for low and high-temperature performance.
SAE Gear Oil Viscosity Grade Requirements
|
Requirements |
SAE Viscosity Grade | ||||||
|
|
70W | 75W | 80W | 85W | 90 | 140 | 250 |
|
Kinematic viscosity, cSt @ 100°C Minimum Maximum |
4.1 - |
4.1 - |
7.0 - |
11.0 - |
13.5 <24. |
24.0 <41. |
41.0 - |
|
Brookfield viscosity Max temp, °C for 150,000 cPs |
-55 | -40 | -26 | -12 | - | - | - |
API Service Designations in Current Use
GL and MT are the API designators for service categories for gear lubricants. MT is for manual transmissions alone while GL designations cover both manual and complex gears. First consider the GL designations.
GL-1
This designation denotes lubricants intended for manual transmissions operating under such mild conditions that straight petroleum or refined petroleum oil may be used satisfactorily. Oxidation and rust inhibitors, defoamers and pour depressants may be added to improve the characteristics of these lubricants. Frictional modifiers and extreme pressure additives shall not be used.
Untreated oil is generally not a satisfactory lubricant for many passenger car manual transmissions because of the operating speeds and loads involved. However, untreated oils may be used successfully in some truck and tractor manual transmissions. In all cases the transmission manufacturer's lubricant quality recommendations should be followed.
GL-4
This designation denotes lubricants intended for axles with spiral bevel gears operating under moderate to severe conditions of speed and load or axles with hypoid gears operating under moderate speeds and loads. These oils may be used in selected manual transmission and transaxle applications. The manufacturer's specific lubricant quality recommendations should be followed.
Although this service designation is still used commercially to describe lubricants, some test equipment used for performance verification is no longer available. Procedures to define this performance are currently being reviewed for adoption by ASTM.
+GL-5
This designation denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high-speed, low-speed, high-torque, and shock-load conditions. Lubricants qualified under U.S. Military Specification MIL-L-2105E (formerly MIL-L-2105D) satisfy the requirements of the API GL-5 service designation. Performance test details are in ASTM Publication STP-512A, "Laboratory Performance Tests for Automotive Gear Lubricants Intended for API GL-5 Service."
API GL-5 quality gear lubricants possess adequate extreme pressure characteristics for essentially all automotive gear applications to prevent wear, pitting, scoring and ultimate gear failure, along with protection against oxidation, thermal degradation, rust, copper corrosion, foaming and water emulsification. API GL-5 oils are relatively equivalent to MIL-L-2105E gear lubricants (see below) and are the most widely used automotive gear lubricants in North America for automobile, truck, bus and heavy construction equipment applications.
Military MIL-PRF-2105-E
|
US Military Symbol |
GO-75 |
GO-80/90 |
GO-85/140 |
|
NATO Symbol |
0-186 |
0-226 |
0-228 |
|
SAE Viscosity Grade |
75W |
80W-90 |
85W-140 |
|
Kinematic viscosity, cSt @ 100°C Minimum Maximum |
4.1 - |
7.0 - |
11.0 - |
|
Brookfield viscosity Max temp, °C for 150,000 cPs |
-40 |
-26 |
-12 |
|
Channel Point, °C, max |
-45 |
-35 |
-20 |
|
Flash Point, °C, min |
150 |
165 |
180 |
|
API Service Designation |
GL-5 |
GL-5 |
GL-5 |
MT-1
This designation denotes lubricants intended for non-synchronized manual transmissions in heavy-duty services. Lubricants meeting MT-1 contain thermal stability and extreme pressure additives.
Service Designations Not in Current Use
Due to changes in manufacturers' recommended practices and the unavailability of proper testing hardware, the API Service Designations GL-2, GL-3 and GL-6 are no longer in current use.
GL-2
This designation denotes lubricants intended for automotive worm-gear axles operating under such conditions of load, temperature, and sliding velocities those lubricants satisfactory for API GL-1 service will not suffice.
Products suited for this type of service contain anti-wear or film-strength improvers specifically designed to protect worm gears.
GL-3
This designation denotes lubricants intended for manual transmissions and spiral-bevel axles operating under mild to moderate conditions of speed and load where service conditions require a lubricant exceeding those satisfying API GL-1 service but below the requirements of lubricants satisfying API GL-4 service.
Gear lubricants designated for API GL-3 service are not intended for axles with hypoid gears. Some transmission and axle manufacturers specify API Category "CC" or "CD" motor oils for this service. The manufacturer's specific lubricant quality recommendations should be followed.
GL-6
This designation denotes lubricants intended for gears designed with a very high pinion offset. Such designs typically require protection from gear scoring in excess of that provided by API-GL-5 gear oils. A shift to more modest pinion offsets and the obsolescence of original API-GL-6 test equipment and procedures have greatly reduced the commercial use of API-GL-6 gear lubricants.
Contact us via Email