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Thread: Do not downshift..... do not

  1. #46
    My new thing is downshifting and braking a the same time. It feels really cool on the rare occasion that you do it right.

  2. #47
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by KBasa View Post
    If you mean "don't throw it down a gear and snap the clutch out so the bikes gets all loopy", yeah. But properly matching rpm and smoothly engaging the next gear down isn't a problem at all.
    Yes it is fine - and I was sort of curious on a motorcycle transmission how you can shift it without ever downshifting.. is there some magic here I'm missing.. my motorcycle transmissions are sequential - 1-N-2-3-4-5-6, 6-5-4-3-2-N-1 Somehow I can't figure out how to get from 6th to 1st without downshifting (color me slow today.. )
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders
    '12 R1200R - I love this bike!

  3. #48
    Rally Rat
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    Quote Originally Posted by PGlaves View Post
    A brief technical note. Brand new precise splines keep the clutch disk centered in use. As splines wear slop develops in the fit of the splines. So pull the clutch lever with the bike in gear and stationary, releasing the clutch, and gravity can cause the clutch disk to drop slightly off center. Then as soon as the disk is again grasped by the pressure plate/clutch cover it can remain slightly uncentered. This exerts incresed radial loading on the input shaft front bearing. So worn splines can cause or accelerate front bearing failure.

    Whether the cause of the spline wear is angular misalignment, radial misalignment, or lack of lubrication - I would suspect the spline wear led to the bearing failure in the case cited above.
    Thanks for your assessment Paul, you and I talked a bit at the National in WI. I can clearly remember sitting at your seminar when you recommended that oilheads should be torn down for a spline lube around 50,000 miles and the lively discussion that generated within the group. I had about 47,000 miles on mine then, and remember saying to myself that the bike is running good and there is no reason to go in there, at least until the season is over. I suspect the damage was already done in my case, but regardless, your recommendation was right on the ball. I hope others can catch any problems and hopefully prevent these failures by heeding your advice.

    The MOA is lucky to have someone as capable as you in the position of "head wrench." And more importantly, your willingness to share your knowledge with the members at large makes you a huge asset to the organization, not to mention you're a hell of a good guy. I'll hope to see you at some rallies next year, regardless of the brand I happen to be riding. Ever thought about getting technically proficient on Triumphs?

    Anyway, I appreciate all the advice and feedback, and I'll keep you all informed if a miracle happens. At any rate, I gotta ride the bike about 4,000 miles so I can collect the 200,000 mile certificate for the "I love me wall"

  4. #49
    Loose Cannon flash412's Avatar
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    Quote Originally Posted by PGlaves View Post
    ...gravity can cause the clutch disk to drop slightly off center.
    Unless I missed something, the clutch disk can drop slightly due to gravity only when the input shaft is not spinning. That would require the clutch to be disengaged and the bike not moving or require the clutch to be disengaged and the trans in neutral for tens of seconds (with more time for warmer oil and less for cold). Otherwise, the clutch disk will be coaxial with the input shaft, due to centrifugal force being a whole lot greater than gravity.

    Did I miss something? Maybe the clutch disk isn't balanced properly?

    Back on topic... Never downshift? Never upshift either. Hell, never turn the ignition key to the "on" position. SHEESH!
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  5. #50

    Unhappy New Guy...But Same Conclusion..

    [QUOTE=Motorcyclist;288778]Thanks for the advice cjack, and in my case, that has all been done. I have the old parts, and even the oil that was drained out of the transmission (BMW hypoid gear oil). I have offered to have them inspect the parts (in my presence), as did the dealer when the bike was in the shop. My family has a 45 year relationship with the dealership owner, so I believe they fought as much as they could for me. We'll see what happens. As has been said before, any product can fail, but how the company deals with the failure determines their true organizational character and whether or not a customer will do business with them again. Having been around BMW's since 1970, I have a pretty good idea of how they will deal with this unless their hand is forced.[/QUOTE]

    Bought my '07 R12GSA on 2-5-07...love the hell out of the bike...bought a BMW for the way it handled and the ease of working on it...also unfortunately because I thought that corporate BMW was a class act...they certainly are anything BUT a class act...obfuscate and deny...I hear contact Customer Service, that is a joke, Customer Service is an independent company hired by BMW NA to filter complaints and placate owners; they are part of the "black hole of information" surrounding any problems with BMW bikes....try to call someone at BMW NA or BMW Germany...hell, even try to email them and get a personal response and not "go talk to your dealer"...

    OK...so I love my bike and think BMW the Company is a piece of ****...that is why I am on forums to learn how to fix and maintain my bike....sad that arrogance and money at some point corrupted BMW and destroyed their credibility..

    Sorry to get off topic...but if premature mechanical failures are not caused by abuse, then the design, materials and workmanship weaknesses that lead to the failures should be openly discussed and corrected by BMW...crap they even keep their dealers in the dark...Grrrrrr.

    Just my opinions...your mileage may vary...
    Phil
    ========
    "In Wallowas"
    ========
    2007 R1200GS Adventure

  6. #51
    Quote Originally Posted by flash412 View Post
    Unless I missed something, the clutch disk can drop slightly due to gravity only when the input shaft is not spinning. That would require the clutch to be disengaged and the bike not moving or require the clutch to be disengaged and the trans in neutral for tens of seconds (with more time for warmer oil and less for cold). Otherwise, the clutch disk will be coaxial with the input shaft, due to centrifugal force being a whole lot greater than gravity.

    Did I miss something? Maybe the clutch disk isn't balanced properly?

    Back on topic... Never downshift? Never upshift either. Hell, never turn the ignition key to the "on" position. SHEESH!
    I said "So pull the clutch lever with the bike in gear and stationary" - think you just stopped at a stop sign. Nothing in the transmission is spinning.

    Radial pressure is imposed on the front bearing at least until you then shift into second, at which point it will tend to center - yes, maybe. Not a perfect example, but take a hula hoop and spin it around your arm and see how well centrifugal force centers it. The physics are the same.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  7. #52
    Loose Cannon flash412's Avatar
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    Quote Originally Posted by PGlaves View Post
    Radial pressure is imposed on the front bearing at least until you then shift into second, at which point it will tend to center - yes, maybe.
    Ok. But why would a radial load hurt a ball bearing (single or double row) or a roller bearing? That is the load for which they are designed. Ball and roller bearings get unhappy with axial loads, which is why proper shimming is so important in transmissions with helical gears.
    Click here for Tales of Motorcycles and Life
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  8. #53
    Quote Originally Posted by flash412 View Post
    Ok. But why would a radial load hurt a ball bearing (single or double row) or a roller bearing? That is the load for which they are designed. Ball and roller bearings get unhappy with axial loads, which is why proper shimming is so important in transmissions with helical gears.
    A ball bearing is designed to take a given radial load - and in the case of a transmission the radial load is not huge, esentially created by the gear mesh in the transmission. I said "excess" radial load.

    I did not make my original comments up. I learned them from a good engineering book on driveline mechanics. Most row crop and hay farmers know fairly well what happens when driveline slop happens in splined connections.

    I suspect we will just need to agree to disagree on this one. I believe it - you don't.

    You also might or might not believe my understanding as to why a damaged driveshaft universal joint caused an output shaft bearing to fail too - but the lab that did the analysis said it was excessive radial force causing a lack of lubrication because the clearances closed up. And this on a bearing designed to take a given amount of radial load.

    We'll just have to disagree I guess.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  9. #54
    rocketman
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    Quote Originally Posted by AntonLargiader View Post
    On what? The guy just keeps saying "do not downshift." Heck, you upshift, you gotta downshift at some point. That's my take on it.
    Well that petty much goes without saying thou....

    I may be having a "senior" moment but it seems to me I once heard/read about a "rotary" transmission where you could just keep shifting up to top gear then the next shift took you back to first, all while moving the shifter in the same direction each time???? course it would make it hard to downshift thru the gears, though I think you could still do that as with any normal trany. As I said I may just be having a senior moment but... anyone else ever heard of this? It was on some two-wheeler as I remember...


    RM

  10. #55
    Cannonball Rider #52 darrylri's Avatar
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    The first foot shifters did not have a "positive stop", so you could shift up or down more than one gear at a time. I bet that made for some interesting riding!
    --Darryl Richman, forum liaison
    http://darryl.crafty-fox.com

  11. #56
    The old "rotary" shifters - sometimes called suicide shifters if I recall correctly - must have been something. You sure better have known when you were in top gear.

    Head off down the road in 1st, shift to 2nd, shift to 3rd, shift to 4th, lose track - try another upshift back in to 1st at road speed - screetch .....

    I'm glad they decided to change that setup.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  12. #57
    Registered User jgr451's Avatar
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    Sorry,what?
    Shirley you can't be serious,don't downshift?

    Reply:"Yes I'm serious.And please don't call me Shirley."
    Sometimes,nothing is a real cool hand.

  13. #58
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    Quote Originally Posted by Wallowa View Post
    Comments are not aimed at BeemerMike but the concept of not using your engine compression to slow bike..

    Geee Wheeezzz...[insert much stronger invective]...I really could care less how anyone rides their bike...that is their business...but don't shut the door on riders that downshift and brake separately or concurrently to slow down...a lot of fine racers and road riders set up their bikes for corners or surface changes by using both the transmission and brakes...to say that brakes are cheaper than transmissions is one of those "when did you stop beating your wife" meaningless comments...

    Good grief folks take a wider view...like Anton said the transmission has to be downshifted at some point...and excellence in riding would dictate that you use ALL the tools in the box...brakes and transmission to name only two..

    Ps...If my BMW will not hold up under decelerating via downshifting...I need to get a different bike..Hey, anybody what to discuss double-clutching or shifting without using the clutch?

    HOLY COW BATMAN!!!

    That's how I feel!!

    Don't downshift to slow the bike? Don't downshift while braking??

    This IS a BMW isn't it? Not some Chinese scooter for $795.00 on E-Bay!
    If my Honda could take repeated downshifting and braking from 160+, this BMW better be able to do it also (or, I'll go get me another Honda!!)

  14. #59
    Rally Rat
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    While I have enjoyed more than one Honda over my 25+ years of constant street-riding (Heck - kept my PC800 Pacific Coast for 11 years!), don't trade in that BMW just yet.

    Constant downshifting in response to velocity changes, terrain, sudden decision making, weather, etc., is all part of normal riding. One matches engine speed to road speed - that's why motorcycles have multiple gears and we shift in the first place.

    My only two cents worth on a thread that has gotten intimidatingly technical (that Glaves guy must be Mr. Wizard in disguise!) is that one must choose the timing of their shifting with care, and release the clutch smoothly.

    For me, riding a motorcycle is more of a graceful dance than Greco-Roman wrestling.

    To each their own.
    Last edited by Greenwald; 02-03-2008 at 05:07 PM.

  15. #60
    Loose Cannon flash412's Avatar
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    Quote Originally Posted by PGlaves View Post
    A ball bearing is designed to take a given radial load - and in the case of a transmission the radial load is not huge, esentially created by the gear mesh in the transmission. I said "excess" radial load.

    I did not make my original comments up. I learned them from a good engineering book on driveline mechanics. Most row crop and hay farmers know fairly well what happens when driveline slop happens in splined connections.

    I suspect we will just need to agree to disagree on this one. I believe it - you don't.

    You also might or might not believe my understanding as to why a damaged driveshaft universal joint caused an output shaft bearing to fail too - but the lab that did the analysis said it was excessive radial force causing a lack of lubrication because the clearances closed up. And this on a bearing designed to take a given amount of radial load.

    We'll just have to disagree I guess.
    Nah, we don't disagree. Clearly BMW transmissions are not designed nor manufactured to carry the loads for the purpose for which they were intended to be used and sold to unsuspecting consumers. It looks like BMWs most recent transmissions were designed by the latest crop of engineering school dropouts, probably the same fellows who (under)design BMW's "famous for sudden and catastrophic failure" rear differentials.

    File a complaint with the NHTSA. Get it on record.
    Click here for Tales of Motorcycles and Life
    - BMW MOA Lifetime Member #18854

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