GS 1200 Drivetrain Backlash....How Much is OK

Discussion in 'GS Boxers' started by 1coolbanana, Aug 30, 2009.

  1. 1coolbanana

    1coolbanana Long timer

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    Hey guys
    Got an 08 GS1200.
    Something Ive been noticing more and more recently, especially in the slow rough stuff, is how much noise and clatter the drive train makes.
    If I put her up on the centrestand, in first gear, I get about 60mm at the tyre OD of backlash.
    Thats all the lash, made up of the whole drivetrain and gearbox I suppose.
    Is this normal or do I have an issue?
    Can someone try this on their 1200 and tell me what they get please?
    Thanks
    Marc
    #1
  2. BerndM

    BerndM Shiftless One

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    Mine is an 06 R1200GS and I just measured 50mm. I'm pretty sure our gear ratios a slightly different so this probably explains the slight difference between my 06 and your 08.
    Hope this helps
    Regards
    Bernd
    #2
  3. 1coolbanana

    1coolbanana Long timer

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    Thanks Bernd.
    So I can assume its about normal then?
    Two to three inches of snatch must be good then :evil
    Cheers
    Marc
    #3
  4. jpooch00

    jpooch00 Been here awhile

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    I've watched several youtube vids of R1200's doing steep, rough hills etc. and they do seem to make a lot of mechanical noise. In a couple, somebody off-camera comments like they "sound like a tractor", and they kinda do.
    #4
  5. BerndM

    BerndM Shiftless One

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    I'm a total noob when it comes to riding on dirt. Taking some tips from others with waaay more experience than me, I found that my GS is much smoother by NOT using 1st gear except for starting out. 2nd gear was much much better. These big boxers don't seem to mind a bit of lugging. The knock sensors work great.
    Regards
    Bernd
    #5
  6. 1coolbanana

    1coolbanana Long timer

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    I find my biggest issue is going downhill, 1st gear too tall and no engine braking when you need to crawl down. End up all on the brakes.
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  7. grantsdad

    grantsdad Been here awhile

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    In a dog-clutch transmission like the one used in the GS there is quite of bit of built-in lash. There should be a few thousandths in the FD, then a few more (very few) in the drive shaft splines, then more yet in the dog clutches on the gears and slider hubs. If that's not enough lash for you, there's more yet in the torsion-damper spring on the input shaft.

    The question is, "how much is acceptable?" That question can only be answered by the Engineers at BMW and/or Getrag, the manufacturers of the gearboxes.

    [​IMG]

    In this photo you can the dog teeth on the slider align with the clutch slots on 4th gear.
    #7
  8. 1coolbanana

    1coolbanana Long timer

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    Torsion bars in the input shaft!!!!! I thought they were reserved mostly for power steering input shafts in cars. Didnt know BMW used them for gearbox input.

    So have much have you got then?
    And what do you consider acceptable?
    #8
  9. jpooch00

    jpooch00 Been here awhile

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    I didn't know these trannys had torsion dampers. If you have a pic, could you post it?

    Many thanks,

    John
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  10. grantsdad

    grantsdad Been here awhile

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    From what I can tell there is no adjustment for lash or endplay in the gearbox. The gaps between the dog teeth and drive slots is machined into each component. It is what it is. That is until a component fails.

    Lash in the FD would be adjusted similar to any other ring/pinion gear assembly by adjusting the pinion gear or the ring gear. I have not dissasmbled a BMW FD therefore I am not qualified to explain how it's accomplished on these units.

    Torsional dampening is achieved by the spring-loaded input shaft. The gear on the input shaft is floating (for lack of a better word). it's turned by a cam-like hub that is fixed on to the shaft. Torsional loads from the input shaft are absorbed by large spring at the back of the hub.

    [​IMG]


    Please forgive the slanted angle of the picture. The input shaft is the one closest to you, on the right.
    #10
  11. jpooch00

    jpooch00 Been here awhile

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    Thank you very much for the torsion damper pic & info! It works just like the compensator on a Harley, same basic design & concept. I'm always learning something new about these bikes from the well informed folks on this forum. :clap

    Thanks again & ride safe,

    John
    #11
  12. 1coolbanana

    1coolbanana Long timer

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    So can anyone else tell me how much backlash they have at the back wheel?
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  13. grantsdad

    grantsdad Been here awhile

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    I can measure my backlash at the wheel; how would you like it reported? Linear distance of the wheel along it's circumference or moment of angle (in degrees) from the hub to the diameter? I think this called degree of arc?

    Since the gaps between each dog tooth and it's corresponding gear are slightly different would you like me to measure the backlash in each gear?

    There is a curious design about the r1200 gearbox. The dog teeth on 1st, 2nd and 3rd are shaped like pentagrams with flat sides loading on the mating gears. 4th, 5th and 6th are 'kidney' shaped with round sides loading on the gears. Why?

    The amount of backlash is different on each gear. This is by design because the shift barrel accuates 3 shift forks, sometimes simultaneously. For example; downshifting from 6th to 5th requires disengaging 6th and engaging 5th. Timing is everything.

    This timing is achieved by the spacing and shape of the dogs/slots on the gears and the pattern milled into the shift barrel/drum.

    The shift barrel is pictured:

    [​IMG]
    #13
  14. 1coolbanana

    1coolbanana Long timer

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    Linear distance is fine. :thumb

    I didnt want to get too complicated here because although very interesting is not what I want to know right now.

    All I want to know is how much backlash is present from a few other peoples bikes at the approximate OD of the back wheel, when in first gear, and on the centre stand.

    Ive got about 60mm, is this comparable to other 1200GS's.

    This is a nearly new bike and my original question was purely to get an idea whether the amount I have is normal and acceptable for a 1200GS or if I should be talking to my dealer about a potential issue.

    Cheers
    #14
  15. Mika S

    Mika S JC & MC: Double Freedom

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    I've got a 2005 and 60 mm on the 1st gear. I'd say you are ok. :nod
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  16. def

    def Ginger th wonder dog

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    Put some moly in your transmission and ride on.
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  17. grantsdad

    grantsdad Been here awhile

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    Please accept my appologies for such a late reply. I've been out of town and away from my bike to perform any measurements until tonight.

    1st: 58.7375mm
    2nd: 58.7375mm
    3rd: 60.3250mm
    4th: 73.0250mm
    5th: 74.6125mm
    6th: 95.2500mm

    Taller gears have more lash on my '07.
    #17