Originally Posted by gonefishn

There have been many threads on transmission fluid before but just wanted to share one more for reference.

Was buying something else when I saw on the shelf three bottles side-by-side of 85W90W fluid with the first labeled GL-4, the second GL-5, and the third GL5+.

Reading the backs, only the GL-4 said protects copper, brass and non-ferrous metals used in synchros.

Bought a bottle and am now torn on replacing the fluid or not. First time I ever came across an only GL-4 rating. The GL-5 stated it met the MIL-L2105 too but did not claim to protect certain metals.

Originally Posted by FFBillysCor

I use NAPA Sta Lube GL 4 Hypoid 85-90. Part # SL24239. Did the research, and decided it was a better choice for 1965-66 Muncie 4 speed MT's. Best,