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Gear oil lubricants are subject to standards aimed at assisting manufacturers, owners and users of vehicles in identifying the proper lubricant to protect their equipment. The most relevant gear oil standards in the commercial sector are issued by the American Petroleum Institute (API), the SAE (Society of Automotive Engineers), ASTM International, and the vehicle manufacturers. Over time, as the performance demands placed on gear oils (both for axle and manual transmission) have increased, there has been less emphasis on the API standards and a greater emphasis on SAE J2360 and especially OEM-specified lubricants.

API Publication 1560 describes API automotive gear lubricant service designations. This document includes the familiar service designations GL-5 and MT-1. There have been several service designations identified in this document over the years, some of which are no longer supported by test procedures to verify that fluids actually meet the requirements. Recently, the API issued the eighth edition of Publication 1560.

Over time, the technical sophistication of drivetrain hardware in passenger car and commercial vehicle sectors has increased. These advances in hardware design have been part of a trend toward more efficient axles, longer service intervals and tougher duty cycles. In addition, improvements in aerodynamics have resulted in increased operating temperatures, placing greater thermal demands on drivetrains. To protect these complex mechanical systems, gear oil additive technology has also continued to evolve. Accurate performance standards, with current and relevant test procedures to verify that lubricating fluids meet those standards and offer excellent levels of protection (rather than merely adequate) for a given type of equipment, are perhaps more important today than ever before.

The eighth edition of API 1560 includes a number of key changes from the previous edition. These updates modernize this document by clearly defining service designations which are in use and, most importantly, those which are now out of use and effectively obsolete. One of those listed as “in-use” in the previous document, and now listed as “no longer in use,” is API GL-1. This is important because API GL-1 denoted lubricants which might be suitable for use in some truck and tractor manual transmissions, but applied such a mild standard that it was not satisfactory for use in modern passenger car manual transmissions. For example, it allowed for the use of straight petroleum oil or refined petroleum oil, neither of which would provide the protection against wear, oxidation, and corrosion offered by a lubricant designed for use in today’s equipment.

As the document states, truck and tractor vehicle and non-synchronized transmission manufacturers have, for some time, preferred the standard API MT-1 instead. At the same time, however, the document warns that API MT-1 does not address the performance requirements of synchronized transmissions and transaxles in passenger cars and heavy duty applications, limiting its value.

Another important change from the previous edition of this updated publication relates to API GL-4, another older designation denoting lubricants intended for axles with spiral bevel gears and selected manual transmissions. API GL-4 is still used commercially, even though test equipment to verify that a lubricant provides this level of performance is no longer available. While the previous document indicated new tests were being sought for API GL-4, this is no longer the case, as no such efforts are underway or planned. Due to a lack of tests- this standard is becoming obsolete.

The new document emphasizes the core designation within API 1560 as API GL-5, with well-defined test requirements that remain current today. Although API GL-5 has been in existence for several decades, it is a key designation when it comes to axle lubricants. It denotes lubricants intended for gears, particularly hypoid gears of the type found in axle differentials operating under a variety of environments, from low speed and high torque to high speed and shock load conditions. The new edition of Publication 1560 also acknowledges the performance specification SAE J2360 as a widely recognized higher level performance specification for automotive gear lubricants. It points out that lubricants approved under the J2360 Standard meet the requirements of API GL-5, but that the requirements of J2360 exceed those of API GL-5. For example, the SAE J2360 Standard contains requirements for elastomer compatibility and gear cleanliness after oxidation that are not contained in API GL-5.

The changes to API 1560 reflect an increasingly complex gear oil market and ever more stringent performance requirements originating at the vehicle manufacturer or supplier level. These parties have emphasized the need for more thorough and severe test requirements. The relevance of the API service designations is being clarified as the industry gravitates toward other ways to define gear oil performance.

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