My Takeuchi calls for sae90. I change the final drive oil frequently but it always comes out gray and dirty and glitter. Is there anything bad with using say Lucas 85w140? I don't use the machine in the winter.
Lower viscosity oils tend to circulate better. Komatsu and some Cat use SAE 30 in their finals. Perhaps next drain, pull the cover for a more complete drain, then you could also get a view of what you have going on in there.
Synthetic oils are far superior than mineral oils in this application but still should be changed at every engine service.
If the original spec calls for an EP SAE 90 oil, try some oil that meets Cat TO-4 spec SAE 50. And not, it's not thinner. Gear oils and engine oils are measured on two different viscosity scales. If the machine works regularly in mud or water oil change periods for final drives should be far less than whatever the OEM manual calls for. Remember it's only a starting point.
How old is the machine and how many hours does the hour meter show? How much do you travel the machine?
2006 Takeuchi tl140. Maybe 1000 hours. I use it for pushing dirt....backfill and grade. I've used mobil 75w-90 in past but when you shake the bottle, it sounds like water. I'm not sure a synthetic is best option.
My TL150s are nearing 10k hrs. Run 90w generic oil in all the finals. Never an issue with them. Heck, I have 9 Takeuchis and that's all I run in the finals. Had to put duocone seals in the drives on s TB180FR once, but that's it. Funny thing though...7 out of 10 times, one final drains darker oil than its twin. Go figure.
10k hours? Wow. It's hard to find sae90. I can only find outboard oil in sae90.
I should have said 75-90W