Back axle oil

[ROGER B]

EP 90 is the recommended grade, but should it be GL4 or GL5 specification?

GL4 is described as OK for most spiral bevel axles and GL5 is for hypoid axles and has high pressure additives, but must not come into contact with 'yellow metals'. I believe the thrust washers in the diff are 'yellow'?

Thank you.

[geoberni]

Well you've said it, Not for use with 'yellow metals', and then you have to know what is in the axle...
But more importantly as far as I'm concerned is that GL-5 is "For use in Axles and Gearboxes where a Hypoid GL-5 gear oil is called for."

So that's the best reason ever for NOT using it.

There's a good explanatory article here: https://takeuroil.com/can-you-use-gl-5- ... 4_Gear_Oil

[ROGER B]

Thank you for the advice and article link. GL4 it is, then!