If that trans wasn't already dead you just killed it.

Can you tell me how please? I would like to know the rationale for putting low shear, low viscosity oil in an extreme duty transmission. I can't imagine why they would do that.

RTFM
 

There's four reasons, mostly having to do with the orientation and design of the case. First off, good luck shifting it in cold weather. After that, it is a tall case, oriented in a somewhat nose-up fashion. Lubrication is splash-driven. With a standard-level fill of heavy oil, the top including the synchros and front input bearing will starve for oil. This is one of the primary reasons the Getrag got a bad reputation - user induced lube failure. Of course the occasional leak would do it with any oil.

Synchromesh is the best oil for the 'Rag.

You cannot compare engine oil to trans oil just by their specs.
They use different ratings. 90 gear is roughly equivalent to 50 engine oil
Redline MTL covers 75W gear oil and 5 W 30 engine oil in the one product.
Seems most syncro oils come up as 75W85.
If you have several days to spare there are endless threads online on the best oil for these.

Assuming you have spent some time in these threads, what was your conclusion?

Thanks for responding, but I can see no compelling reason to run anything besides 85W140
in the G360 transmission. The ‘splash’ concept didn’t work very well because the trans was half full of the thin stuff when it came in growling with bearing noise. Gear oil doesn’t need to splash. It has such great adhesion that is follows the gears up to the top and stays there. It will adhere to a vertical surface for days, even weeks undisturbed. As far as the height or angle of the G360, if there are differences to other manual transmissions, I believe they are negligible. They all sit higher in the front, and if were very much taller it would contact the cab floor. That said however, running 5W30 Full Synthetic oil might be alright because I’ve have seen what synthetic oil can do for a Powerstroke HPO system. It is amazing technology. And by using what the manufacturer recommends I also avoid any liability issues. But if it were my truck, I would definitely use gear oil. I have yet to drive it since I drained out the gear oil and refilled it with the thin stuff, so I don’t know how it’s going to react. If I hear any noise, the gear oil goes back in! lol

Getrags are normally noisy - noisier than alot of other transmissions. How much experience do you have with them? :w2:

As mentioned earlier the original spec was for 5w30 engine oil and times have changed.
Personally I would go with a current transmission 75W85 oil not an engine oil. Viscosity is the same but it is designed for transmissions

That's why synchromesh is "currently" the best Getrag fill.

This was an abnormal transmission noise fellas. It sounded like a bearing going out. It was one of two complaints the owner brought it in for. This is my first encounter with a "rag," as I've heard it called. Seems like a fine transmission, as good as any other gearbox if it is maintained. I noticed all the extra criss-cross webbing cast into the left side, and wondered if it was to compensate for a weak case. It shifts without a clutch with no gear clash, so that says a lot for it.