Owen_Dyneto wrote:
You don't say what type of 75-90 is in it now. Gear oils with slip additives such as would be used in a differential are detrimental in a standard shift synchronized transmission as the slip additives defeat the action of the synchronizers.
Also the heavier oils will help retard gear spin which can benefit shifting.
When in doubt you can't go wrong by using the lubricant Packard recommended.
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