GL-3 and GL-4 : Designed for manual gerboxes with brass parts such as synchronisers, it should only be used in Manual Gearboxes
GL-5 : Designed for Axles / Differentials , they contain twice the Phosphorous as GL-4 oils and they should NOT be used in gearboxes, because it will corrode the brass synchronisers and make them slip ( noisy shifting ), you can only use these in differentials, and reciprocally GL-4 should not be used in a differential because it lacks the Phosphorous Extreme Pressure additives.
GL-6 : not currently in use.
You may find some oils that are GL4 and GL5 rated, i would not use these and use an oil that only meets GL-4 instead ( ensures low amount of phosphorous ).
Guide to gear oils
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Guide to gear oils
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Oil and Coolant guru
Finnish but born and raised in Spain.
Oil and Coolant guru
Finnish but born and raised in Spain.