I want to change the gear lube in the 46 trans, and have been told to NEVER use a synthetic lube, because they are all rated GL-5. Use a dino based GL-4 instead.
Went out yesterday to Wally world and three auto stores and found no GL-4. Autozone had Coastal brand 80/90, with service listed of GL-5, GL-4, and GL-3, on the same bottle. So far in my investigation that claim doesnt even make sense, because GL-3 has ZERO Extreme Pressure additive, which is essential to reduction of gear wear. Can anyone shed some light on gear lubes? Newer vehicles maybe up into the 60's or 70's may have the same requirements and therefore problems. If so it is starting to look like GL-4 is a special order item, perhaps going the way of leaded gas.
I would like to know what the difference is in GL-4 and 5. Tried searching www and pulled up some company sites without luck.

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46 1/2 ton with 56 292:thumbsup:

I have used this before:
http://www.bestsynthetic.com/lubes.shtml

Thanks for the link. The AGT,ALM variety of Amzoil gear lube sounds like the right stuff. Synthetic, GL-4 but not GL-5. I'm going to try to find someone local who is a dealer.

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46 1/2 ton with 56 292:thumbsup:

You cannot go wrong using Amsoil....i've trusted it for years old vehicles and new models.

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...... BRIAN ......