Final Drive Oil weeping?

[R1100RT]

Is it normal for some final drive oil to weep from the rubber boot that connects the final drive unit to the rear portion of the universal joint of a 1998 R1100RT?

I just want to know if this is just something that happens to most of these units or if I have to do a few things to continue my quest for 100,000 miles on this bike before I look for another. I notice some weepage of final drive oil on the underside of the rubber boot which will accumulate a residue on the swing arm bracket. I have over 66,500 miles and change the final drive oil once a year with a synthetic 75W-90 oil. I average almost 15,000 per season. I had the dealer grease the splines last winter and they didn't notice anything abnormal then. I don't see that the final drive oil level had dropped much. So I am just wondering if the slight weepage is something that just needs to be cleaned and not concerned about.

Thanks for your sage advice.

[Motorcyclist]

A picture would help, but it sounds like you have either the FD pinion shaft seal going, or the transmission output shaft seal.

[Jfixit]

I had the same question and received excellent advice from Paul Glaves. After checking for abnormal movement of the rear wheel (everything seemed fine) I loosened the boot by taking the zip ties off, gave it a quick inspection and wiped the oil out of the boot. New zip ties and 2000 miles later no oil showing. I think many bikes weep a little. I think it is normal.

[Red100RT]

I had the same question and received excellent advice from Paul Glaves. After checking for abnormal movement of the rear wheel (everything seemed fine) I loosened the boot by taking the zip ties off, gave it a quick inspection and wiped the oil out of the boot. New zip ties and 2000 miles later no oil showing. I think many bikes weep a little. I think it is normal.

I agree. I have noticed that if I haven't ridden the bike for awhile (month or two) the final drive seals will leak a bit then stop. I have had cars do this especially with the rear motor seal. I have an '81 airhead that does the same thing with the trans seal.

[DrPaul]

Maybe not normal but quite common. As I understand, it is usually the pinion seal rather than the transmission output shaft seal that is the culprit. Overfilling the FD might contribute to the problem. Be sure to drain and fill the FD on the center stand and fill only to the lowest thread of the fill hole. As long as you check the level and don't let it get too low, no harm should come to the FD from this issue alone.

[Mr. Frank]

It's pretty common. I replaced my pinion gear seal at 25K miles and again at 88K. In most cases it's a matter of cleanliness more than function in that the level of oil in the final drive doesn't go down much. You might switch to 80W90 dino gear oil. Sometimes that does not leak as much. If you periodically drain the boot and monitor the oil level you can see how serious the problem is and decide what you want to do.

[jduke]

If the oil is inside the boot, more than likely it is the pinion gear seal. It's not supposed to and with all the problems with the FD on these bikes I would get it fixed. If the pinion gear is moving slightly and causing this you could easily have major damage if not fixed. That's exactly what mine did and I pulled it off and sent it to Anton. The pinion gear was loose and the gears were out of mesh.

[R1100RT]

Looks like I need to look at the pinion gear seal. Thank you to all that posted your comments. The forum is a great way to learn from others and not always have to pay the full price of tuition while learning how to maintain our BMWs.