Hey Guys,
I bought my '73 GX Coupe (A15, Original 4-speed Gearbox, Original Diff) about a year ago with a lot of vibration and whining down the driveline. The first thing I was advized to do was squeeze about half a cup of copper compound grease into the diff with ATF and the 85W gear oil. The gearbox just got ATF. Its been a year and the vibration has quieted down quite a bit.

I'm thinking of replacing the diff and gearbox oil this afternoon and I was wondering if anyone had advice or hints on the type of oil I should use. Maybe some mixes that work better? In example, a friend of mine mixes a third of his diff oil with another type of oil into his GTX's diff. I just can't remember what it was. =/

I live in South Africa, I do just as much highway driving as I do bumper-to-bumper driving, and the the drivetrain's (original) been hammered by an A15 for 10 years.

Any advice or hints would be appreciated.

don't use GL5 oil in your box, they will harm the gears. i use Pennzoil 80/90W GL4 in my box and 140W GL5 in diff. no problem at all, smooth shifting.

I go gl4 and 1/3rd atf. My mechanic swears by it and speaking with a member here tgat built race boxes he says it stops the gearbox oil frothing up as much.