Generally, I assume that the API oil service designations are all one needs to know about what lubricants to use. Yesterday, I bought Valvoline High Performance 75W-90 Gear Oil and my local NAPA store to fill my fresh 67 M-21. However, the label on the back says "recommended for hypoid differentials (conventional and limited slip) where API GL-4 or API GL-5 is specified and non-synchronized manual transmissions where API GL-5 fluid is specified" without a mention of synchronized transmissions.
Is there a special GL-5 designation for non-synchronized transmissions? Is GL-4 and GL-5 for differentials different from the GL-4 designations discussed here as appropriate for Corvette 4-speeds? Is there any reason why I should not use this stuff?
I was hoping to fill the trans today, and I hope one of our oil experts can enlighten me.
Is there a special GL-5 designation for non-synchronized transmissions? Is GL-4 and GL-5 for differentials different from the GL-4 designations discussed here as appropriate for Corvette 4-speeds? Is there any reason why I should not use this stuff?
I was hoping to fill the trans today, and I hope one of our oil experts can enlighten me.
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