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Thread: Slipper Clutch and Friction Zone

  1. #16
    Quote Originally Posted by ncpbmw1953 View Post
    I have no troubles w/ the clutch from brand new '16 to now 27K miles--it's wonderfulThat is a sampling group of one experience. I love the easy clutch level pull force required The lever effort has never been the issue or even mentioned in this discussion. You just need to respect its narrow zone especially when the bike is cold.JUst because there is a poor design OR implementation does not mean you have to RESPECT it
    There were two issues in this post from the beginning. First was what BMW calls a "judder" issue, which I will come back to. Then there was the issue of friction zone. I mistakenly linked the slipper function to the problem because this was a new clutch on the wethead which had the slipper function. Adding that function to the wethead wet clutch may or may not have caused the original issue.

    MCN has posted reviews of both the GS and RT where they experienced the judder issue. I had numerous replies on several forums complaining of the "wonderful" friction zone and then a group started to form talking about the over fill reservoir issue. On my GS, sampling group of one, the clutch reservoir WAS DEFINITELY over filled. I corrected that AND in the process discovered that the first lever adjustment point worked really well for me. Those two items FOR ME solved the friction zone issue. I do NOT know if the the judder issue is solved but I have not experienced it even when in situations where I had run into it before. Now this is the kicker! Finding a BMW service manager who recognizes that judder exists is like finding the Holy Grail. Well, on the 2017 wethead transmissions there is NOW a judder damper. Hmmmm. Do you think they put that on for decoration?
    Old But Not Dead
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  2. #17
    Quote Originally Posted by chewbacca View Post
    There were two issues in this post from the beginning. First was what BMW calls a "judder" issue, which I will come back to. Then there was the issue of friction zone. I mistakenly linked the slipper function to the problem because this was a new clutch on the wethead which had the slipper function. Adding that function to the wethead wet clutch may or may not have caused the original issue.

    MCN has posted reviews of both the GS and RT where they experienced the judder issue. I had numerous replies on several forums complaining of the "wonderful" friction zone and then a group started to form talking about the over fill reservoir issue. On my GS, sampling group of one, the clutch reservoir WAS DEFINITELY over filled. I corrected that AND in the process discovered that the first lever adjustment point worked really well for me. Those two items FOR ME solved the friction zone issue. I do NOT know if the the judder issue is solved but I have not experienced it even when in situations where I had run into it before. Now this is the kicker! Finding a BMW service manager who recognizes that judder exists is like finding the Holy Grail. Well, on the 2017 wethead transmissions there is NOW a judder damper. Hmmmm. Do you think they put that on for decoration?
    Well, it's no problem for me, judder, friction zone. What I do not appreciate is the N>1st gear clunk, so I avoid it. It clearly is an engineering design defect IMO. Fortunately one can avoid it, but one also feels the basic problem when downshifting into first as well, the lack of separation when the clutch is pulled. What's weird to me is: I can be decelerating in 2nd gear as I'm approaching a full stop. Now if I put the bike in N, then let the clutch out while I'm rolling along at just a few MPH, then if I pull in the clutch lever and apply gentle downshift pressure it slips into first with zero clunk. Why can't I come to a full stop then pull in the clutch and put it in 1st and not have it clunk? Just rolling a few MPH prevents the clunk. I wonder what the basic cause is for this? We note when the bike is cold and ambient less than about 60F, there is no N to 1st clunk. It must have to do w/ heat-related expansion of adjacent parts, despite oil that gets a little thinner as it heats up.

  3. #18
    Quote Originally Posted by ncpbmw1953 View Post
    What I do not appreciate is the N>1st gear clunk, so I avoid it. It clearly is an engineering design defect IMO.
    I just went into the garage to see what the clunk was like on my bike. I don't even think about it because as I had thought before I tried it, it isn't that bad on mine. Now when I had a 2011 GS it was a significant clunk. On GS's it seems to be just a normal fact of life kinda thing. Heard people talk about it for a long time. On three Triumph triples and two FJR's it was never as pronounced as on the GS's. IIRC no bike I ever had had a consistent clunk like the GS either. I feel a lurch when it goes into first in addition to the clunk. For me, it ain't no big thing as long as it stays the same and doesn't get louder and the bike doesn't start to move.
    Old But Not Dead
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  4. #19
    Dress for fall & avoid it AlanColes's Avatar
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    Quote Originally Posted by ncpbmw1953 View Post
    Well, it's no problem for me, judder, friction zone. What I do not appreciate is the N>1st gear clunk, so I avoid it. It clearly is an engineering design defect IMO. Fortunately one can avoid it, but one also feels the basic problem when downshifting into first as well, the lack of separation when the clutch is pulled. What's weird to me is: I can be decelerating in 2nd gear as I'm approaching a full stop. Now if I put the bike in N, then let the clutch out while I'm rolling along at just a few MPH, then if I pull in the clutch lever and apply gentle downshift pressure it slips into first with zero clunk. Why can't I come to a full stop then pull in the clutch and put it in 1st and not have it clunk? Just rolling a few MPH prevents the clunk. I wonder what the basic cause is for this? ...
    Different people have different levels of sensitivity to mechanical sounds, 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. Some prefer to have the more raw sound of the BMW tranny as it provides a quicker audabile clue to any tranny issues, while others prefer to have a more insulated and removed experience. Just a matter of which flavour you prefer.

    Quote Originally Posted by ncpbmw1953 View Post
    ... We note when the bike is cold and ambient less than about 60F, there is no N to 1st clunk. It must have to do w/ heat-related expansion of adjacent parts, despite oil that gets a little thinner as it heats up.
    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.


    Quote Originally Posted by chewbacca View Post
    I just went into the garage to see what the clunk was like on my bike. I don't even think about it because as I had thought before I tried it, it isn't that bad on mine. Now when I had a 2011 GS it was a significant clunk. On GS's it seems to be just a normal fact of life kinda thing. Heard people talk about it for a long time. On three Triumph triples and two FJR's it was never as pronounced as on the GS's. IIRC no bike I ever had had a consistent clunk like the GS either. I feel a lurch when it goes into first in addition to the clunk. For me, it ain't no big thing as long as it stays the same and doesn't get louder and the bike doesn't start to move.
    Depending on the amount/degree of the "lurch" it could be normal (if it is minor and goes away immediately) or an adjustment issue (if it produces a constant pull on the bike).

    As for the 2011 GS there is very little to compare as it uses a dry-clutch which makes a significant difference on sound and feel to a wet-clutch. What is common is that BMW in the past have never worried too much about tuning out "normal" sounds and cluncks on their Boxers, that occur in all trannies but are engineered out by most everyone else, so when they went to the wet-clutch on the Boxer they didn't tune that out as much as they have on their G, F S, and K models.
    Regards, Alan - President BMWONS - MOA Charter Club #097, BMWMOA/BMWRA/BMWONS/Airheads
    Current: '14 R1200RT / '06 Ducati ST3s / '91 R100GS / '86 R80RT / '75 R90S / '73 850 & '70 750 Commando Prev: '04 R1150RT / '81 Honda GL1100 / '77 Suzuki GS750 / '73 Norton 850 Commando

  5. #20
    Alan,
    Excellent post; however, sound was never a part of the OP. Sound was an inserted issue just a few posts ago. The "judder" does have a sound associated with it but that was never the issue or even mentioned IIRC. The issue was that the clutch engaged then disengaged in rapid succession causing the front end to hop. There was NO slipping of the clutch between engagement and disengagement. It is like a machine gun, engaged, disengaged, over and over until you pull the clutch lever all the way in. You start to slip the clutch in a normal fashion then the judder begins. It's not fun because it usually occurs in places where balance is an issue. Whether the elves in the Black Forest think that is just something for one to get accustomed to or not may be subject to a readjustment of thinking if NHTSA gets involved. If you ever experience it, it will be obvious it is a very dangerous event. Judder is like alcoholism, the first step is to get out denial and admit it exists.

    P.S. - the lurch is not significant. Lots of bikes do it to some degree. Yes you can compare dry and wet clutches if all you are comparing is the sound. The 2011 had a louder clunk than the 2016, just a fact.
    Old But Not Dead
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  6. #21
    Dress for fall & avoid it AlanColes's Avatar
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    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?
    Regards, Alan - President BMWONS - MOA Charter Club #097, BMWMOA/BMWRA/BMWONS/Airheads
    Current: '14 R1200RT / '06 Ducati ST3s / '91 R100GS / '86 R80RT / '75 R90S / '73 850 & '70 750 Commando Prev: '04 R1150RT / '81 Honda GL1100 / '77 Suzuki GS750 / '73 Norton 850 Commando

  7. #22
    Quote Originally Posted by AlanColes View Post
    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.
    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!

  8. #23
    Quote Originally Posted by ncpbmw1953 View Post
    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!
    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.
    Old But Not Dead
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  9. #24
    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.
    Old But Not Dead
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  10. #25
    Dress for fall & avoid it AlanColes's Avatar
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    Quote Originally Posted by ncpbmw1953 View Post
    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!
    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
    Regards, Alan - President BMWONS - MOA Charter Club #097, BMWMOA/BMWRA/BMWONS/Airheads
    Current: '14 R1200RT / '06 Ducati ST3s / '91 R100GS / '86 R80RT / '75 R90S / '73 850 & '70 750 Commando Prev: '04 R1150RT / '81 Honda GL1100 / '77 Suzuki GS750 / '73 Norton 850 Commando

  11. #26
    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.
    Old But Not Dead
    Semper Fi

  12. #27
    Registered User lkraus's Avatar
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    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!
    Larry
    2006 R1200RT

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