I changed out my final drive oil at 1500 km, way before the recommended changeout. Two observations:
1) The oil level was not full, because when I removed the upper check/fill bolt nothing overflowed out.
2) On removing the lower drain bolt, what came out was unexpectedly dirty, with lots of visible particles suspended in the oil. I would call it almost silt-like.

On that note, I would recommend to all Swing owners that they do their first final drive oil changeout when you do your first oil change. It's really cheap insurance to make sure the final drive lasts a long time. I used Shell synthetic 75W-90 gear oil.

[quote="bigbird"]I changed out my final drive oil at 1500 km, way before the recommended changeout. Two observations:
1) The oil level was not full, because when I removed the upper check/fill bolt nothing overflowed out.
2) On removing the lower drain bolt, what came out was unexpectedly dirty, with lots of visible particles suspended in the oil. I would call it almost silt-like.

On that note, I would recommend to all Swing owners that they do their first final drive oil changeout when you do your first oil change. It's really cheap insurance to make sure the final drive lasts a long time. ]I used Shell synthetic 75W-90 gear oil.[/quote

"I used Shell synthetic 75W-90 gear oil." Since the shop manual calls for 10W-30, I hope you aren't making a big mistake with that gear oil.

OK, I drained the gear oil in the final drive, installed motor oil (Shell Rotella T6 synthetic 5W-40) with the JASO MA rating required by Honda , ran the bike for several minutes while spinning the rear tire on the stand, drained that new oil, and installed another dose of motor oil. I didn't use Honda oil (never have, never will), as it is not anything special. Engine oil is made by oil companies, not by motorcycle companies.
I use only Shell lubricants. That's because the aerospace company I am associated with only specifies Shell lubricants in their overhaul of gas turbine engines. This is a very large world class company that does billions of $ of business worldwide. They would never cheap out on lubrication. There is a reason they specify Shell lubrication. I figure I can't go wrong with their products for car or bike.

In Googling gear oils, I found this:
"It is important that purchasers check the oil against the vehicle manufacturer's specification to ensure it does not contain any aggressive chemicals that may attack gear components, such as the phosphor bronze used in many Japanese boxes."

So, as I wipe the humble pie off my face and say I was wrong about using gear oil, I again thank the many contributors here who are civil, patient, and helpful.
Terry

I asked a friend of mine for his comments. He has owned and fettled many bikes and scooters and knows them inside out - he owns currently an X9500 and a Nexus 500 (this replaces a T-Max).
He regularly completely disassembles his scooters for overhaul and is a mine of information.
Here are his comments:

It depends on the cut of the gears and the pressure loading on the teeth as they mesh.
Cut appropriately as per for example the old mini, where the gears were in the sump, they are perfectly fine lubed with ordinary (mineral at the time) engine oil. Otherwise most gearboxes would use hypoid 80 or 90 gear oil.
A lot of modern cars now though use the much thinner automatic transmission fluid in their manual gearboxes.
The thinner the oil the less drag. Also being almost a hydraulic oil ATF will take huge pressure loads. You would think that a thicker oil would give better protection but that is not the case as it's also slower to move around and gets churned up more and is slower to settle back into the 'sump'.
I would guess for the small relatively low torque scooter final drives, any oil will be OK. If we were talking a manual primary gearbox as in most bikes, then they generally are lubed by the engine oil. This would probably indicate that the 'standard gear tooth profile' generally in use by the motorcycle industry as a whole will be appropriate for this type of oil, and Suzuki, Honda and Yamaha in particular will more than likely retain this standard in their scooter final drives.

I found this most interesting and reassuring.

I had 2 mid-80s Accords with manual transmissions, and both of them used regular 10W-30 (or thereabouts) engine oil in the transmissions. I never had a problem with those cars, so that's another reason I've personally been comfortable with using engine oil in the SWing. I also like not having to go out and buy different (and more expensive) oil just to do the change on the final drive

Back many moons ago when I was a youth There were friends at the local drag strip who used automatic transmission fluid in their manual transmissions and swore by it.
Craig

My two bobs worth! ( USA residents please read as 2c)

When I owned my Range Rover, I made the mistake of using the Hypoid 90 grade gear oil in the gearbox. Luckily I mentioned it to a fellow RR owner and found out that this beast only could run on regular motor oil as the thicker oil would put excessive strain on the oil pump and the sulpher in the hypoid would mix with condensate to form sulphuric acid which in turn ate out the brass/bronze bearings. This was borne out with further discussions with RR mechanics.
The hypoids have a distinctive "sulpher" smell.
Big differences viscosity and or ingredients in recommendations by the OEM's is there for a reason.

Thanks Jeff, did mine today, your pictorial saved me heaps of time.