I have a 1996 R1100R.
I wanted to buy oil for the Gearbox and Final Drive, but at the time of purchase I had not looked into the manual to see what was used from new.
To make a longer story shorter, I was told by the dealer that they use 75w-140 synthetic. My book says either 80 or 90 Hypoid gear oil or 80w-90 Hypoid gear oil. So what is the real story. I have read people have been using the synthetic in both. This however does not make any sense to me. Is this why there are so many bearing failures in the final drive, by using the synthetic. It is not even close the viscosity of the stock oil.
Any rider reports or long term use reports (same) would be helpful. My gut feeling is go with the stock oil.
I switched to all synthetic at about 20k miles on my R1150R. Never regretted it. Over 43k now, and the bike runs fine.
If you don't mind the extra cost, synthetic is great for high mileage boxers.
If you want to use regular oil, that is fine too.
I find synthetic makes my bike feel smoother.
Owner's manuals will not recommend synthetic oils, but they do not hurt.
What you should pay attention to is the octane rating recommendation for fuel.
If I run under 89, my bike pings. And the manual says "89".
As far as drive failures go, they are not related to oil, but factory installed shims.
2 things to watch for:
Weeping oil from the rubber boots on the drive, gathering on the rear wheel.
Mostly in the back due to gravity.
OR
Metal shavings on the magnetic final drive plug.
If either of these things happen, stop riding, and get a mechanic to inspect the drive.
I was able to save big bucks several years ago, as catching a problem early was the difference between a $125 repair, vs. thousands for a new drive. There is a MCN article by Paul Glaves that explains the shim issue, and sure enough, my mechanic described the same exact problem, without ever reading the article.
I don't recall 1996 models suffering from this much though, it came on in later models, but I could be wrong.
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