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Old 08-30-2009, 03:26 AM   #1
1coolbanana OP
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GS 1200 Drivetrain Backlash....How Much is OK

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
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Old 08-30-2009, 09:52 AM   #2
BerndM
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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
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Old 08-30-2009, 04:04 PM   #3
1coolbanana OP
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Snatchiness

Thanks Bernd.
So I can assume its about normal then?
Two to three inches of snatch must be good then
Cheers
Marc
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Old 08-30-2009, 04:20 PM   #4
jpooch00
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Quote:
Originally Posted by 1coolbanana
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
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.
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Old 08-30-2009, 05:34 PM   #5
BerndM
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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
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Old 08-30-2009, 06:01 PM   #6
1coolbanana OP
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Goin Down

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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Old 08-30-2009, 09:59 PM   #7
grantsdad
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dog clutches

Quote:
Originally Posted by 1coolbanana
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
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.



In this photo you can the dog teeth on the slider align with the clutch slots on 4th gear.
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Old 08-30-2009, 10:41 PM   #8
1coolbanana OP
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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?
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Old 08-31-2009, 02:30 AM   #9
jpooch00
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Question

Quote:
Originally Posted by grantsdad
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.



In this photo you can the dog teeth on the slider align with the clutch slots on 4th gear.
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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Old 08-31-2009, 05:12 AM   #10
grantsdad
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no adjustment

Quote:
Originally Posted by 1coolbanana
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?
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.




Please forgive the slanted angle of the picture. The input shaft is the one closest to you, on the right.
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Old 08-31-2009, 05:21 AM   #11
jpooch00
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Thumb

Quote:
Originally Posted by grantsdad
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.




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

Thanks again & ride safe,

John

jpooch00 screwed with this post 09-01-2009 at 02:34 AM
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Old 08-31-2009, 02:14 PM   #12
1coolbanana OP
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Snatchiness

So can anyone else tell me how much backlash they have at the back wheel?
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Old 08-31-2009, 06:45 PM   #13
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unit of measure?

Quote:
Originally Posted by 1coolbanana
So can anyone else tell me how much backlash they have at the back wheel?
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:

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Old 08-31-2009, 07:20 PM   #14
1coolbanana OP
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Linear distance is fine.

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
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Old 09-01-2009, 01:15 PM   #15
Mika S
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I've got a 2005 and 60 mm on the 1st gear. I'd say you are ok.
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