[UBZ]

So I put new aftermarket gears in the 410 transfer case , did the whole rebuild thing as one does .
This led me down the rabbit hole of what oil to run .

I have always used 80w/90 in the xfer and diffs . Castrol EPX Axle GL5 normally and never had any issues
However recent reading has given me the impression that I should be running a GL4 oil in the xfer due to the 2x bronze thrust washers on the counter gear.

What oil are people running ? GL4/ GL5?
I could use something like Redline MT90 at the high end of the scale or I see penrite do a 75w90 GL4 oil. Getting harder to find these days .

However trail logic says use the same easy to get oil in as many places as possible
so would prefer to use the same oil as in the diffs , and leave the spendy oil for old 4 speed gearbox

[fordem]

Read your labels - there are yellow metal friendly GL5 oils.

The GL5 designation has to do with the level of EP (Extreme Pressure) additive protection, and the problem with GL5 oils and bronze (or brass) is that the sulphur which was commonly used would attack the "yellow metals", newer formulas don't have the same sulphur content.

I've been running Mobil One full synthetic 75W90 GL5 in manual transmissions (with brass synchros), transfer case (again, brass synchos) and front & rear diffs for over twenty years now with no issues.

[sideways]

I run the Penrite 80w-90 GL5 gear oil. It says it is safe for copper alloys. It's quite cost effective in a 20L too.

https://penriteoil.com.au/products/gear ... 90-mineral