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Mack 12Speed gear oil?


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My '77 12 speed tranny is supposed to take 80w90 gear oil acording to the TS442 service manuals.

However the common practice at the local Mack dealership is to use 85w140 gear oil.

Comments or thoughts?


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In SAE grade GO-H you can use 90, 80W-90, 80W-140, 85W-140, 140.

In SAE grade GO-H/S....................75W-90, 75W140, 80W140.

All can be used above and below temps of 32 degrees.

You should be good to go.

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It doesn't cost anything to pay attention.

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