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rotorwrench · 08-09-2019, 05:27 PM

The original MIL spec for gear lube all carried the 2105 designation so that alone isn't a very good indicator. I'd say that older slow moving heavy equipment would likely use GL1 spec lubricant. Where it gets confusing is when they tell you to use MT1 which is a GL5 spec for non synchro transmissions in busses & trucks. They say it is backward compatible with GL1 but I think they are full of it too. I wouldn't be as worried about the synchro blockers as I would the gear bushings and thrust washers.

SAE-90 GL1 or a good quality SAE-50 motor oil would work since both are the same basic viscosity. They're just rated using different equipment. GL1 with a good anti corrosion additive would be the one to find for the price. A person may have to order a drum of it to get some for a good price. It's all expensive now days.

All the old tractors used GL1.

08-09-2019, 05:27 PM	#9
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: GL 1 oil The original MIL spec for gear lube all carried the 2105 designation so that alone isn't a very good indicator. I'd say that older slow moving heavy equipment would likely use GL1 spec lubricant. Where it gets confusing is when they tell you to use MT1 which is a GL5 spec for non synchro transmissions in busses & trucks. They say it is backward compatible with GL1 but I think they are full of it too. I wouldn't be as worried about the synchro blockers as I would the gear bushings and thrust washers. SAE-90 GL1 or a good quality SAE-50 motor oil would work since both are the same basic viscosity. They're just rated using different equipment. GL1 with a good anti corrosion additive would be the one to find for the price. A person may have to order a drum of it to get some for a good price. It's all expensive now days. All the old tractors used GL1.