Transmission "Klunk"- what is the actual mechanical explanation? - K-Bikes.com - Excellence in Motion
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post #1 of 50 (permalink) Old Jun 7th, 2008, 9:54 am Thread Starter
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Transmission "Klunk"- what is the actual mechanical explanation?

We talk about it, but I've never heard a detailed- for-the-layperson explanation of just exactly WHAT the KLUNK sound from the transmission is during shifting. Mine KLUNKS like HELL into first gear, even after 12k miles. It usually does it from first through third, but If I really try, I can finesse into second and third. If nothing else, it is an embarassment to have it work this way.

So what are the parts that are getting so abused? After 12k, I simply can't imagine parts slamming toegther like that are going to survive too long.

Could someone with the knowledge PLEASE take the time to explain just what is getting slammed so hard, and why?

Thanks-

B.
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post #2 of 50 (permalink) Old Jun 7th, 2008, 10:27 am
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It's not what you'd expect, actually the gears in the transmission are in constant mesh. They do not themselves engage and disengage.

It's the slamming together of the dog teeth on the sides of the gears than makes the clunk.

http://auto.howstuffworks.com/motorcycle2.htm

http://auto.howstuffworks.com/sequential-gearbox1.htm

Last edited by JCW; Jun 7th, 2008 at 11:37 am.
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post #3 of 50 (permalink) Old Jun 7th, 2008, 10:34 am Thread Starter
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so they are going to slam so damn hard all their life they are going to eventually send shrapnel everywhere? That's what mine sounds like going into first from a dead stop.
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post #4 of 50 (permalink) Old Jun 7th, 2008, 11:51 am
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Klunk is good.

It means that the dogs have fully engaged and you're ready to go.

Trying to quiet the cluck by foot shifting slowly or not completely only damages the dogs and leads to transmission damage.

If you keep the input and ouput shafts moving at close to the same speeds, the less the cluck. That means a brisk upshift, not speed shifting, but not loligagging either. On downshifts, revving the engine to match speeds will help too. When the bike is stopped, the output shaft is still and the engine/input shaft are rotating at idle speed. Fully clutching the bike will slow the input shaft a little, but it still moves due to some clutch drag. Holding in a couple seconds fully allows the shaft to slow maybe a little more and may help with the clunk, but don't ride the clutch, it'll wear out the bearings.

Last edited by JCW; Jun 7th, 2008 at 11:58 am.
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post #5 of 50 (permalink) Old Jun 7th, 2008, 11:59 am
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Speaking of transmission damage: I was out on the Colorado/Utah border for a few day ride w/ some friends and shifted into 5th and it sounded and felt like the bike was being hit with a sledgehammer...but only in 5th gear and only when applying power. Made it back home by skipping 5th gear.

The report is that the dogs were extremely worn and that 4th was looking like it was going to fail shortly, so BMWNA is replacing the entire tranny under warranty.

Once again I gotta say: I got a lemon and it is in the shop more than I am out riding. I have started a dialogue w/ BMWNA and I am waiting to see what they are willing to do about the unending problems w/ this bike. Will keep ya'll posted.

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post #6 of 50 (permalink) Old Jun 7th, 2008, 3:20 pm Thread Starter
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Quote:
Originally Posted by JCW
Klunk is good.

It means that the dogs have fully engaged and you're ready to go.
Baloney. There isn't ANYTHING good sounding as the tranny SLAMS into first gear while sitting at a stop light.

BAM! = NOT good.

I just got a GS and that thing shifts like someone built a tranny right. I'm tellin' ya, something is NOT good with this design. "Being hit with a sledgehammer" is an accurate description.
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post #7 of 50 (permalink) Old Jun 7th, 2008, 3:56 pm
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It's probably happening on your car but you are far away, well insulated from the rear axle and there is much more mass in the drive line.

If we had a belt or chain from the tranny output shaft to the rear wheel you probably wouldn't hear anything. As it is, we have a shaft drive with splines, UJ couplings and a gear rear drive, so some backlash is to be expected.

I don't think clunks are anything to worry about compared to oil leaks and other problems. Nobody wears out gears or splines and whilst the rear drive crown and pinion is relatively large and beefy, it's the bearing or seal that will get you first.

If you slip the clutch out slowly at stops, you can take up the slack and mitigate clunks most of the time.



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post #8 of 50 (permalink) Old Jun 7th, 2008, 7:04 pm
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While stopped and in neutral try holding the clutch squeezed for a minimum of two to three seconds before tipping from neutral to first and you won't here a thing.

Shifting from 1st to 2nd to 3rd takes a little more concentration: the clutch is just a very brief "brush" not a meaty squeeze; the shift itself, has to be snappy and precise, more of a "flick" than a poke. And the throttle must be consciously unspooled. Put all that together, just right, without thinking about it too hard and your bike will ride just like mine: smooth and quiet.

I hear lots of other bikes; like Japanese, shaft-driven cruisers and even some sport bikes make a lot more shifting noise than mine.

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post #9 of 50 (permalink) Old Jun 7th, 2008, 7:31 pm
 
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Ive put 12500 miles on my 07GT in 10 months living in Seattle, this bike has always been a heavy shifter at low speeds and the gearbox has developed an annoying growl at idle sometimes very pronounced. The dealer says this is normal, any feedback on this.
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post #10 of 50 (permalink) Old Jun 7th, 2008, 8:23 pm
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Well, mine clunks like hell too, but so did my old RT, and it never left me stranded so I got to believe it's just a Beemer thing.

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