I have a '65 C2 with the 327 and 4 speed manual that I have rescued from a 20 yr storeage and have been working on for almost 2 yrs now. Have replaced & cleaned many things...at the stage now to change fluids...
Seen many comments for and against Gl-4 and GL-5, and even comments to be sure and look for a MT-1 designation, etc, some recommending amsoil GL-5....
What is the recommended fluid for the transmission and the rear end?
Ok to use synthetic or stay with mineral based oil?
Thank you
James
60k miles on C2 in Dallas

I have a '65 C2 with the 327 and 4 speed manual that I have rescued from a 20 yr storeage and have been working on for almost 2 yrs now. Have replaced & cleaned many things...at the stage now to change fluids...
Seen many comments for and against Gl-4 and GL-5, and even comments to be sure and look for a MT-1 designation, etc, some recommending amsoil GL-5....
What is the recommended fluid for the transmission and the rear end?
Ok to use synthetic or stay with mineral based oil?
Thank you
James
60k miles on C2 in Dallas

You can spend as much as you like for exotic "hot-rod" lubricants, but it isn't necessary. The trans and diff were designed, tested, and durability-validated using ordinary 75W90 and 80W90 gear lube (plus the GM Limited-Slip additive if it's a Posi diff), and they'll work just fine. GL-5 for the diff, either GL-4 or GL-5 for the transmission.