Manual transmission lube
Thread Starter
Instructor
Joined: Sep 2009
Posts: 135
Likes: 2
From: Waterbury CT.
Manual transmission lube
I have a '72 LT-1 with 4 speed tranny. I want to change tranny gear lube. I have some 80W90 that says good for non-synchronized transmissions with OEM spec API GL-5/MT-1 oil. My '72 Chevy manual lists SEA 80 or 90 GL-5 gear lubricant. Are these compatible, or is there an additive left out that should be in a synchronized tranny or is it understood that it is okay for regular synchronized transmissions?
Thanks for any advice you can add.
Thanks for any advice you can add.
Le Mans Master
Joined: Mar 2004
Posts: 7,507
Likes: 1,513
From: Little Rock AR
Your owners manual does not spec GL5.
Old school GL4 is best for vehicles that were originally spec'd for it. People will tell you what they have had sucess with but you can't go wrong using the stuff it was originally designed to use. It just works right.
I tried a heavily advertized brand of expensive synthetic GL5 for a few days in a fresh built Muncie that I put together. It made more noise, leaked and did not shift a smooth as it should. Drained it out and put CHEAP generic parts store GL4 conventional gear oil and never looked back. Don't fall for the hype.
Old school GL4 is best for vehicles that were originally spec'd for it. People will tell you what they have had sucess with but you can't go wrong using the stuff it was originally designed to use. It just works right.
I tried a heavily advertized brand of expensive synthetic GL5 for a few days in a fresh built Muncie that I put together. It made more noise, leaked and did not shift a smooth as it should. Drained it out and put CHEAP generic parts store GL4 conventional gear oil and never looked back. Don't fall for the hype.
Race Director
Joined: Mar 2017
Posts: 11,970
Likes: 4,521
From: Virginia
Red Line makes synthetic GL-4 gear oil (Amazon Link). I use it in my B&W 4-speed, and in the differential.
