Problem finding conventional 75w90 gl4 gear oil

mattwithcats · Jun 26, 2021

Another suggestion is Mobil 1 Delvac 50...

Learn how Mobil Delvac 1™ Transmission Fluid 50, a full synthetic, manual transmission fluid, was designed to provide maximum engine protection.

www.mobil.com

ripcord · Jun 26, 2021

You do NOT need GL-4 in a 1970 Mustang 8 or 9 inch rear end. There are no yellow metals in those axles and any GL-5 gear oil will work fine.

MolaKule · Jun 26, 2021

mattwithcats said:
Another suggestion is Mobil 1 Delvac 50...

Not for a differential with a Hypoid design.

SOHCman · Jun 27, 2021

Use any GL-5 gear oil you wish for a hypoid differential. GL-4 is not suitable protection.