Hi all, and thanks for letting me join your community.

I just purchased a 2010 Concours 14 about a month ago. Since then, I've put about 800 miles on it and have loved every minute of it.

After about the first 150 miles, I notice some black spray on the inside of my left rear wheel. I didn't think anything of it at first. It has progressively gotten worse to the point where it really caught my attention today. There's no oil leaking on the ground or anything, but I started looking around to see if I could find the source.

What I found has really disturbed me. It looks as though there's a hole where there should not be one next to the rear end drain plug. It's definitely the source of the spray, which I assume now is gear oil. I'm honestly concerned to even ride it at this point because I don't know if it even has any gear oil in it, although none has leaked on the ground as of yet.

I've included some pictures and am hoping if you guys can tell me how bad this is. What really gets me is that the dealership I purchased this from assured me the bike had just been serviced and there were no major issues found. I hope I'm wrong, but this seems pretty major to me.

Let me know your thoughts. Thanks in advance!

**Edit: Much to my relief, I have been able to find some pictures of some final drives for sale that look as though they also have this hole. Perhaps this is just grease from when they serviced the bike, or I have a small final drive leak somewhere inside the case?

Possibly too much grease on the spline, or a leaking seal. Figuring out whether it is grease or oil will tell you which. The last pic looks like oil. Either case needs the wheel removed, which is one of the easier jobs on this bike.

Or, you could just give it a good clean and see if it reappears.

My guess is someone overfilled the rear drive gear housing because they didn't follow the manual.   But could be a leaky seal.  Just check your level and if OK, I would clean off the wheel and give it time to see if it gets better.

Rear drive oil has it's own special smell.  Spline grease usually doesn't smell like rear drive oil.  Someone could have got very ambitious with greasing the rear spline and the grease got thrown out.  When I've greased mine up (every tire change) I've only used the Molybdenum grease (Honda    ) and sparingly at that.  We've seen issues with seals as well.  Overfilling the rear drive will cause added internal pressure.  I've never filled mine to the point where it's come out of the filler hole and I've never had an issue with seals.  Clean it all off and check the rear drive oil level.  Hopefully the previous owner did not over tighten the filler plug.  I would start there. 

Overfilling the rear drive will cause added internal pressure.  I've never filled mine to the point where it's come out of the filler hole and I've never had an issue with seals.

Once, I apparently did.  The first time I changed it, I might have overfilled it a little, and I ended up with the exact same symptoms and presentation as the original poster.  But it only lasted a few weeks and then was fine.

Clean it all off and check the rear drive oil level.  Hopefully the previous owner did not over tighten the filler plug.  I would start there. 

Looks like we are all in agreement

Rear drive oil has it's own special smell.  Spline grease usually doesn't smell like rear drive oil.  Someone could have got very ambitious with greasing the rear spline and the grease got thrown out.  When I've greased mine up (every tire change) I've only used the Molybdenum grease (Honda    ) and sparingly at that.  We've seen issues with seals as well.  Overfilling the rear drive will cause added internal pressure.  I've never filled mine to the point where it's come out of the filler hole and I've never had an issue with seals.  Clean it all off and check the rear drive oil level.  Hopefully the previous owner did not over tighten the filler plug.  I would start there.

Thank you all for your responses! I really appreciate it. I'm inclined to think that this is probably spline grease, as the rear tire was just put when I purchased the bike, and when I get a bunch of the stuff on my finger it doesn't really have a smell at all (or it's so subtle that I can't notice it). I'll see if I can get the drain plug open today and give it a look.

Thanks again!

Thank you all for your responses! I really appreciate it. I'm inclined to think that this is probably spline grease, as the rear tire was just put when I purchased the bike, and when I get a bunch of the stuff on my finger it doesn't really have a smell at all (or it's so subtle that I can't notice it). I'll see if I can get the drain plug open today and give it a look.

Thanks again!

Yep, gear oil has a VERY distinctive smell to it and it's impossible not to notice.

Don't remove the rear drive drain plug! You want to open the filler plug to check the level.

Place the bike on the center stand and open the filler plug. The oil level should be just touching the bottom threads for the filler plug. Don't rotate the tire while you're checking! The gears will pick up the oil and you won't get an accurate reading. 

I was just about to mention both of those notes...
Never remove the drain plug, before making sure you have the "fill" plug removed... Some times those damned fill plugs are wayyyy tight, and many people have had difficulty getting them out, and end up damaging them... then, as they had already drained the rear drive... they couldn't fill it up.. till they got the fill plug fixed...

also, when checking the "fill" level, make sure the bike has sat stationary for about a half hour, and do not rotate that rear tire... They probably over filled it when it was serviced, by doing just that, turning the tire really allows it to be overfilled drastically.. the level should just touch the threaded portion of the hole, and not "overflow".. even on the side stand... this causes premature internal seal failure.

Over greasing that drive spline also causes a lot of spooge, I do mine on every tire change, but I make sure to completely clean off all of the old grease. I admit, I don't use the moly grease, I find it extremely messy, I just use a high quality bearing grease (I have 2 types, and both are different colors, one is red, the other is bright blue) and can tell if I over greased by the color if it "flings some out", I use it pretty sparingly these days, as I have acquired enough times to figure out "just right" and doing it every 5-6K miles, that grease is fine.

Yep, gear oil has a VERY distinctive smell to it and it's impossible not to notice.

Yeah, it is a pretty gross smell.  I can't quite describe it, but nothing smells quite like it.

Don't remove the rear drive drain plug! You want to open the filler plug to check the level. Place the bike on the center stand and open the filler plug. The oil level should be just touching the bottom threads for the filler plug. Don't rotate the tire while you're checking! The gears will pick up the oil and you won't get an accurate reading.

+1  Perfect info.  Easy to do/check.

Yeah, it is a pretty gross smell.  I can't quite describe it, but nothing smells quite like it.

+1  Perfect info.  Easy to do/check.

In my teenage years, we always described that smell as "Ohhhhh crap, this is gonna cost me a bunch of $$$$$$$"

My guess is someone overfilled the differential because they didn't follow the manual.   But could be a leaky seal.  Just check your level and if OK, I would clean off the wheel and give it time to see if it gets better.

The C14 does not have a "differential", it has a rear drive housing. The only need for a differential is if it has two rear drive wheels.

Dan

The C14 does not have a "differential", it has a rear drive housing. The only need for a differential is if it has two rear drive wheels.

OK, "rear drive" it is!

I always fill mine on the side stand, seems to always get the right amount in, with no spray. I had what you are showing in the pics when I overfilled the first time I changed oil.

Another tech Tip, is to loosen the fill screw before removing the drain. Someone may have tightened it too much to be easily removable.