Gear Oil
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Joined: Dec 2016
Posts: 82
Likes: 16
From: Hampden MA
Gear Oil
Hate to bring this up with all the confusion and contention I see out there, but here goes. I want to change out the Gear oil in my transmission and rear end. I think I should be using 80W90 GL4 gear oil. Not GL 5 or synthetic. I am looking to confirm. I have a 1969 427\390 M20 4 speed car. If GL4 is the preferred way to go, where would it be available?
Safety Car
Joined: May 2004
Posts: 4,351
Likes: 1,579
From: los altos hills california
My new transmission M20W warranty requires I use this.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Race Director
Joined: Mar 2017
Posts: 11,931
Likes: 4,497
From: Virginia
I went with Red Line full synthetic, 75w90 GL-4. This, too, was based on much searching on the forum, and the ability to use the same oil in the (manual) transmission as in the differential. It seemed to improve the transmission, but I don't have any miles on the (Dana 44) differential yet.
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The Gearbox video with the Youtube channels all recommend GL4 and even have a video on why. The Synthetic is so slippery it wont stay on the gears long enough to make it back to the top and lube the bearings. On of then even had a unit returned with the bearings toasted because of no lube. I rebuilt mine last winter and can row through the gears as fast as I can with zero noise or grind. Its like butter
Last edited by Rescue Rogers; Jul 28, 2018 at 09:01 PM.