Gear Oil Spec Difference in GL4, GL5 and MT1

[M.D. Holloway]

had a few questions concerning different gear oil specs. Hope this helps.

Service Designations in Current Use:
GL-1: 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. Friction modifiers and extreme pressure additives shall not be used.

GL-4: 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 transmissions and transaxle applications where API MT-1 lubricants are unsuitable.

GL-5: Denotes lubricants intended for gears, particularly hypoid gears, in axles operating under various combinations of high-speed shock loads and low-speed, high-torque conditions. Lubricants qualified under MIL-L-2105D satisfy the requirements of the API GL-5 specification, although the API designation does not require military approval.

MT-1: Denotes lubricants intended for nonsynchronized manual transmissions used in buses and heavy-duty trucks. Lubricants meeting the requirements of API MT-1 provide protection against the combination of thermal degradation, component wear and oil seal deterioration. API MT-1 does not address the performance requirements of synchronized transmissions and transaxles in passenger car and heavy-duty applications.

[Bill Verburg]

As far as a 915 is concerned only GL5 or MIL-L2105B are acceptable

[M.D. Holloway]

Additional info on the two different requirements:

GL5s have to show resistance to corrosion in the presence of moisture, resistance to gear distress under low-speed, high-torque conditions, resistance to gear distress (scoring) under high-speed, shock-load conditions, oxidation stability.

MT-1s have to show thermal and oxidative stability and deposit resistance, seal compatibility, transmission cyclic durability, spur gear wear resistance, reduced foaming tendencies, stability in the presence of copper and copper alloys.

[Jeff Alton]

What is the best for a G50 box that sees some track time?

Jeff

[KobaltBlau]

IMHO regular over the counter Mobil 1 75w-90 is good for all around use in a G50, including track use. Red Line 75w-90 should be good too. you don't need the 75w-90ns, 75w-90 will be good.