Slipper Clutch and Friction Zone

It had been some time since I read the initial post, and I didn't re-read the first portion when replying. Ahhh, the mind gets lazy. ;-)

That gives me a better understanding of what you're experiencing. Unfortunately, while I have plenty of experience with both wet and dry clutches and have rebuilt a few, I'm definitely no expert and your experience has me scratching my head.

Should be able to eliminate the slipper-clutch as a culprit, however, as it works on deceleration only.

It sounds as though it might almost be that the clutch plate is grabbing at low speed. Many years ago when I worked on my Norton clutches some folks would run across a similar scenario if there was certain contaminates on the plates, others would make them slip but certain ones would make them grab initially and it took a bit for them to release.

Has it occurred in both 1st and 2nd gears? Any other gears?

AlanColes said:

It is the reverse of what you are thinking. As the oil heats it gets thinner (both in it's amount on the parts and in it's viscosity). Therefore it has less of a dampening affect on the sound.

....but if your bike sounds similar to the "typical" wethead, than there is nothing actually wrong with the tranny-clutch setup, it is just that BMW has never concerned itself much with masking the mechanical sounds of it's transmissions. They are normal sounds that are simply engineered out of most other bikes.

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I don't see any way slightly thicker oil, especially 0/40W at 60F, is sufficient to dampen the BIG clunk you get when you put the bike into first. No way. Go to ambient of 66F and you'll get the clunk on a cold start. I don't know the full anatomy of the clutch assembly but what seems like is happening is there are adjacent rotating parts that clunk more the greater their differential rotational velocity. If they were BOTH essentially stopped, there would be no clunk beyond slight as gears mesh. My sense is that as parts heat up tolerances are tighter such that one rotating part starts to get dragged into turning by another adjacent gear/part, and so this creates the clunk that worsens as the bike warms. The role of heated thin oil I was surmised would decrease the tendency for adjacent rotating parts to 'drag along' a neighbor.

That's an interesting rationale. Yes, they didn't bother to engineer out a substantial clunk--gee, I wonder why the other bikes bothered to simply engineer out those normal sounds!

ncpbmw1953 said:

I don't see any way slightly thicker oil, especially 0/40W at 60F, is sufficient to dampen the BIG clunk you get when you put the bike into first. No way. Go to ambient of 66F and you'll get the clunk on a cold start. I don't know the full anatomy of the clutch assembly but what seems like is happening is there are adjacent rotating parts that clunk more the greater their differential rotational velocity. If they were BOTH essentially stopped, there would be no clunk beyond slight as gears mesh. My sense is that as parts heat up tolerances are tighter such that one rotating part starts to get dragged into turning by another adjacent gear/part, and so this creates the clunk that worsens as the bike warms. The role of heated thin oil I was surmised would decrease the tendency for adjacent rotating parts to 'drag along' a neighbor.

That's an interesting rationale. Yes, they didn't bother to engineer out a substantial clunk--gee, I wonder why the other bikes bothered to simply engineer out those normal sounds!

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I agree with the above. BMW's have had a reputation for clunky transmissions for as long as I can remember; however they seem to work ok.

Alan,
I'm sure about 1st gear but not so sure about any other gear because when this happens both hands are busy, one or both feet are busy and you are concerned about the bike falling down.

Back in the late 70's or early 80's, the USMC had about 32 AV8 Harriers crash. The Marines were putting experienced pilots in them because they were hard to fly. The USMC came out with a finding that it was pilot error. (the USAF had made similar findings where they blamed the pilot and not the plane). My point is that it is easy to say the GS is OK, it is the rider that is at fault. As was previously stated, BMW KNOWS that there is an issue because they have modified the 2017's and up.

I have ridden Honda's, Kawasaki's, Triumph's and BMW's since 1965. I will take a manually actuated clutch over a hydraulic ANY DAY. But I don't have that option. The conclusion I have come to is I have adjusted the lever and actuation as best I can and I'm aware of the problem and where it occurs. So I'm more careful.

ncpbmw1953 said:

I don't see any way slightly thicker oil, especially 0/40W at 60F, is sufficient to dampen the BIG clunk you get when you put the bike into first. No way. Go to ambient of 66F and you'll get the clunk on a cold start. I don't know the full anatomy of the clutch assembly but what seems like is happening is there are adjacent rotating parts that clunk more the greater their differential rotational velocity. If they were BOTH essentially stopped, there would be no clunk beyond slight as gears mesh. My sense is that as parts heat up tolerances are tighter such that one rotating part starts to get dragged into turning by another adjacent gear/part, and so this creates the clunk that worsens as the bike warms. The role of heated thin oil I was surmised would decrease the tendency for adjacent rotating parts to 'drag along' a neighbor.

That's an interesting rationale. Yes, they didn't bother to engineer out a substantial clunk--gee, I wonder why the other bikes bothered to simply engineer out those normal sounds!

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You are misstating what is happening with the oil. Yes, it is a multi-grade, 0W-40, but the W stands for winter and don't think that it ever gets to an actual 0 viscosity. Cold 0W-40 is sufficiently thicker cold than at operating temperature (engine oil needs to be at least 220 degrees F to burn off all the deposits and accumulated water vapor). There are real and significant acoustic dampening differences between cold engine oil and engine oil at proper operating temps.

The clunk, if it is the ubiquitous BMW clunk as the OP appears to be suggesting, isn't from the clutch, it is from the transmission and there are many reasons for it.

Spacing of parts, spin-down and spin-up times, etc., all change as the transmission heats up and when completely cold (at startup), everything is a bit of a compromise for many parameters. Also, BMW has traditionally used more technically intricate castings than most other manufacturers for several reasons. These are lighter and stronger, but transfer much more noise than the less expensive typical motorcycle castings that are thicker and heavier.

As for sound itself, there is a very real correlation between oil temperature and the sounds heard on my Airheads, my past Oilhead and my Wethead. My Norton and Ducati tranny sounds are far less sensitive to this than my BMW trannies.

YMMV

Alan,
Again, I agree with most of what you said, but as a veteran of a zillion oil threads I would like to make the following comment. xW40 means the operating viscosity of the oil at operating temps is 40 weight. As you stated the 0W or whatever W is the cold or startup viscosity. The answer is more complex than that because it involves lots of other factors such as base stock extenders to achieve the range of viscosity values but the short answer is that 40 is truly the most important factor.

Just IMO, the additive package in the oil you use has more impact on the clutch slippage than the viscosity.

Motorcycle Consumer News also spoke of the problem in an October, 2013 review of the R1200GS:
"The new 8-plate wet clutch is a big change. Unlike the automotive
style dry clutches used on previous boxers, the wet clutch
promised to be a big improvement as it should easily handle more
abuse without overheating in demanding off-road conditions.
And perhaps it could have been a purely positive experience,
except that BMW chose to fit a centrifugal pressure plate assist
to reduce lever effort and provide a back-torque limiting effect.
While its lever effort is commendably light, such a design also
changes engagement feel with rpm, becoming lightswitch sudden
at higher revs. Attempting jackrabbit starts from lower revs, the
clutch didn’t generate adequate grip, oddly grabbing and releasing
for a hopping launch that didn’t inspire admiration. From
high revs, its sudden action made wild wheelies too likely, so
conservative launches were the only way to go, and we didn’t
set any records as a result."

This description seems to be saying that the "centrifugal assist" and the slipper effect may in fact be due to the same mechanism. Still sounds like the only way to prevent a hopping launch is to have the clutch fully engaged before the rpm gets very high?

Hey, that sounds like the skill needed for the older dry clutches!

Vindicated!!!

Thanks for the information, Larry. I say vindicated because I knew something was not right and got the feeling from some respondents on the several forums I posted this topic on that it was clearly a case of OPERATOR ERROR. As the song says "I'm no angel" or in this case "no expert" on clutches. I've been a trouble shooter most of my life so when BMW changed to a hydraulic clutch with slipper features my first suspect for the problem source was the new clutch. Even though I now know there is a problem, at least now I can compensate for it. Thanks.

I always thought that sensation (hopping) was the traction control kicking in but now I think it's a result of the effect described here. I've never had a bike with traction control so that was my initial impression ... then again, this is my first bike with a slipper clutch of any kind too. I do know that the bike is very easy (too easy) to wheelie with a passenger but not so much riding solo. Always wondered why the traction control didn't step in there ... makes much more sense now.

AlanColes said:

You are misstating what is happening with the oil.... There are real and significant acoustic dampening differences between cold engine oil and engine oil at proper operating temps.

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Alan, I said nothing about 'cold engine oil' vs 'engine oil at proper operating temps...' that is your reframing of the point I was making.

What I did say was that on a COLD START at AMBIENT of maybe 66F and up you get the clunk IMMEDIATELY, before engine oil or transmission has changed appreciably, whereas as below that you don't get the clunk until the engine runs for a few minutes. This suggests the source of the major difference is more to do w/ expansion of the parts involved, versus 'acoustic dampening differences' from changes in the oil. You're comment seems to suggest when OIL temp is 62F, major dampening happens, whereas when OIL temp is 66F minimal dampening effects are happening. No way, no how! It's as you mentioned later, 'Spacing of parts, spin-down and spin-up times, etc., all change as the transmission heats up and when completely cold' is essentially what I said in other words, 'My sense is that as parts heat up tolerances are tighter such that one rotating part starts to get dragged into turning by another adjacent gear/part, and so this creates the clunk that worsens as the bike warms.'

ncpbmw1953 said:

Alan, I said nothing about 'cold engine oil' vs 'engine oil at proper operating temps...' that is your reframing of the point I was making.

What I did say was that on a COLD START at AMBIENT of maybe 66F and up you get the clunk IMMEDIATELY, before engine oil or transmission has changed appreciably, whereas as below that you don't get the clunk until the engine runs for a few minutes. This suggests the source of the major difference is more to do w/ expansion of the parts involved, versus 'acoustic dampening differences' from changes in the oil. You're comment seems to suggest when OIL temp is 62F, major dampening happens, whereas when OIL temp is 66F minimal dampening effects are happening. No way, no how! It's as you mentioned later, 'Spacing of parts, spin-down and spin-up times, etc., all change as the transmission heats up and when completely cold' is essentially what I said in other words, 'My sense is that as parts heat up tolerances are tighter such that one rotating part starts to get dragged into turning by another adjacent gear/part, and so this creates the clunk that worsens as the bike warms.'

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My misunderstanding/misreading. I was thinking that your clunk was like mine, most pronounced at cold startup (oil at ambient (60F-80F mostly) and not after the bike has been run for a while (oil at 180F-210F).

Boy........these new bikes are com-pli-kated
OM

ncpbmw1953 said:

Alan, I said nothing about 'cold engine oil' vs 'engine oil at proper operating temps...' that is your reframing of the point I was making.

What I did say was that on a COLD START at AMBIENT of maybe 66F and up you get the clunk IMMEDIATELY, before engine oil or transmission has changed appreciably, whereas as below that you don't get the clunk until the engine runs for a few minutes. This suggests the source of the major difference is more to do w/ expansion of the parts involved, versus 'acoustic dampening differences' from changes in the oil. You're comment seems to suggest when OIL temp is 62F, major dampening happens, whereas when OIL temp is 66F minimal dampening effects are happening. No way, no how! It's as you mentioned later, 'Spacing of parts, spin-down and spin-up times, etc., all change as the transmission heats up and when completely cold' is essentially what I said in other words, 'My sense is that as parts heat up tolerances are tighter such that one rotating part starts to get dragged into turning by another adjacent gear/part, and so this creates the clunk that worsens as the bike warms.'

Click to expand...

BMW motorcycle transmissions clunk. They always have. Some less than others but they clunk. In 1977 I got off a Yamaha triple and onto an R60/5. The first time I shifted from 1st to 2nd I actually looked back and down to see what had broken and fallen off the bike.

PGlaves said:

BMW motorcycle transmissions clunk. They always have. Some less than others but they clunk. In 1977 I got off a Yamaha triple and onto an R60/5. The first time I shifted from 1st to 2nd I actually looked back and down to see what had broken and fallen off the bike.

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Apparently BMW decided enough people found their proprietary clunk objectionable enough to make revisions for at least some 2017 water boxer designs. Good for them as there is nothing inherently pleasing about clunking transmissions, especially the N>1st gear clunk.

ncpbmw1953 said:

... people found their proprietary clunk objectionable ...

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While folks might like to categorize things this way, it is not the case. Nothing proprietary about it.

ncpbmw1953 said:

... Good for them as there is nothing inherently pleasing about clunking transmissions, especially the N>1st gear clunk.

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For/to you. But that isn't everyone.

I have no such aversion to the relatively un-muffled sound of the BMW transmission, I actually prefer it's honesty.

BMW transmissions are known to last as long or longer than most.

Perhaps haven't ridden many touring Harleys. Like BMWs, they will happily rack up hundreds of thousands of worry-free miles but the trannies have a very definite audible clunk to them. They are just doing their job with less muffling than other makes.

No one is forced to buy one, but also, no one should really complain about something that has been a known fact for decades. Buy Honda and you'll know you've shifted gears when the gear-indicator confirms it - that's a gross exageration, but there is a real difference just like there is with the Boxer engine. I had a Gold Wing but perfer the BMW Boxer to the Honda Boxer. If a person doesn't like the basic characteristics of a specific vehicle why did they buy it in the first place? Well, sometimes it takes owning/riding several bikes until we identify what it is that we like the most and what we don't care for or want. There are plenty of choices out there and most all of them are very good bikes, just different approaches and flavours, which is absolutely great for all of us.

PGlaves said:

BMW motorcycle transmissions clunk. They always have. Some less than others but they clunk. In 1977 I got off a Yamaha triple and onto an R60/5. The first time I shifted from 1st to 2nd I actually looked back and down to see what had broken and fallen off the bike.

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My first Oilhead ride had me a bit worried I broke H's bike

I think the biggest clunk I have experienced is a K 1200 Wedge idling high at start up and nudging it into 1st....EVERYONE turns to look I mean CLUNK And it's a wet clutch as well.

I have ridden several Wetheads and haven't thought about it at all.

Clunk or Hop, that is the question?

As the bard from Avon once said, to be or not to be, that is the question! Well this this thread has drifted mightily to clunk or not to cluck, is that a question??? Lots of bikes clunk. Some more so and others less. Really I am much more concerned about how well they shift, and does the clunk cause a problem with shifting. Although we have danced around this but how the transmission is designed and built has a lot to do with it. All the bikes I have ridden, if you pull in the clutch, you still get the clunk so the clutch usually isn't the clunk culprit. That's my 2 cents.

Now, as the OP, the real issue was the hopping problem directly related to clutch activation. IMO, this issue was resolved as a design issue known to BMW. Also, IMO, it is a potentially dangerous situation and worthy of a report to the NHTSA.

Shifting Issues on 2018

chewbacca said:

I found the following in an MCN article directed at the wethead clutch:
"they also have an unfortunate centrifugally energized
pressure plate design that creates control difficulties during hard
launches. Attempt a quick start on the new water-head, and its
clutch will bounce in and out of engagement, making the bike
hop instead of drive forward."
In another review of an RT there was this:
"My only complaint is that, when using the clutch, I found its very narrow friction zone at the end of the lever’s throw difficult to manipulate. Slow speed maneuvering was met with a herky-jerkiness I hadn’t mastered by the end of our ride."
http://www.motorcycle.com/manufacturer/ ... -ride.html

The highlighted sections above seem to be describing exactly what I was experiencing.

When I checked my res level, a bunch of fluid came out indicating it was over filled. There was a thread on AdvRider that point to the tune of several pages. So I think we are getting at the heart of the matter. Whether the slipper function has anything to do with the issue is mute, it is becoming clear that the clutch unit on a GS probably has a mechanical problem in its design.

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When you reduced the amount of fluid in the clutch reservoir did that help with the clutch problems?
My RT is a 2018 with around 1700 miles on the clock has a problem with up shifts.
I have also experienced this engage-disengage symptom during faster take offs from stops.
But my main problem is that as the motor heats up during a days ride, the shifting action gets worse.
When cold I can shift from Neutral to First gear with no noise and no Lurch. When Hot, it makes a lot clunk and will jump a foot or so, unless I lock down the brakes. It is as if the clutch doesn’t completely separate.
Also the warmer the motor/transmission gets the worse the shift action between Frist and Second gear is, using the clutch. The shifting is very “notchey”, like you can feel the engagement of the gear teeth in the foot pedal. A few times it got stuck in Neutral and I was not able to shift into Second without coming to a stop or using very excessive force.
The bike does have the Gear Change Pro system and it works down shifting with no problems. Upshifting is another story. I gave up on that part. Up shifts make me look like it is my first time using a manual transmission.
The bike has now 1750 miles and it starting doing something similar from Second to Third gear.
I returned the bike to the dealer yesterday.
PS: My HexHead with a 188,000+ miles shifts better.

Hi Bernie,
Yes correcting the fluid level did help, but not a cure. I also have gear change pro but for me it has pros and cons. But I kinda like it. Like I said before, this IS a design and build fault and BMW knows it. They made fixes to the 2018 but not sure if they fixed it. For me just knowing about the issue has allowed me to compensate. It could get someone hurt, but since most guys just blow it off it will not really be fixed. Seen that happen before. Still a great bike.

2016 R1200GSW as well. N to 1 clunks once warm, pretty loudly, but usually slick right after cold start up. I sit in neutral most all the time now. Other than that, it works quite well. My 2001 R11S's trans is smoother, however. Gear Shift Pro takes getting used to, as it requires that you just keep the throttle ON through the shift. It's against decades of experience that has one want to do otherwise. But it is some slick piece of kit... as long as your do what it wants.