Problem finding conventional 75w90 gl4 gear oil

[mattwithcats]

Another suggestion is Mobil 1 Delvac 50...

https://www.mobil.com/en/lubricants...products/mobil-delvac-1-transmission-fluid-50

 

[ripcord]

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]

Another suggestion is Mobil 1 Delvac 50...

Not for a differential with a Hypoid design.

 

[SOHCman]

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