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Rattling gearbox

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joerahn
Newbie
Newbie

Posts : 2
Location : Moscow

Rattling gearbox

Post by joerahn on Thu 21 Apr 2016, 5:31 pm

Hello, community!

I used forum search on my problem but since my english skills is fairly poor i didnt got much of it.

So i bought lovely blue CB500 from a friend last year. At the end of the season (we can't ride during winters, yes Sad ) i encountered a problem.
When switching from first to second gear i can hear gearbox clatters (not sure if it is the word i need tho) very loud. So i went home to diagnose a problem.
I find out noise appears when i'm shifting to first gear which is is ok. But also when i'm shifting from neutral to second gear (standing still, clutch pulled of course) i can hear a rattling sound, like sprockets in the gearbox scrape (again, not sure if it's the word) one another.

So i have only two guesses. It's either cluth have excessive freeplay, or problem in the gearbox itself. Following shaft for example, or a thing that mooves sprokets back and forth.
I can't check those right now, but i desided to ask anyway.

I hope my writings can be read without a special dictionary. Smile

Thank you in advance.
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Jameshambleton
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Posts : 2122
Location : Bedale, North Yorkshire

Re: Rattling gearbox

Post by Jameshambleton on Thu 21 Apr 2016, 5:53 pm

Welcome to the forum and it sounds like clutch rattle. I think a few members on here have it although I've not experienced it myself
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jchesshyre
the 900
the 900

Posts : 643
Location : Chester

Re: Rattling gearbox

Post by jchesshyre on Fri 22 Apr 2016, 6:23 pm

Everything you describe is normal, you just need to move the gear lever more decisively. You shouldn't normally be going from neutral to second at standstill. On both CBs I've had, if I do do this just to see what happens then there's a big clunk or the grinding gear sounds that you describe if I'm not firm/quick with the gear lever. 

I'm 99% sure there's nothing wrong with your gearbox. Just make sure you're shifting swiftly - not giving the lever an aggressive kick but a firm, decisive click - and your problem should disappear. Even after racking up loads of miles I still occasionally do a hesitant gear-change now and then which results either in a false neutral when at high speed or the horrible gear grinding sound you describe when at low speed or standstill.
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stormbringer
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Posts : 1231
Location : Aarhus, Denmark

Re: Rattling gearbox

Post by stormbringer on Fri 22 Apr 2016, 7:08 pm

Welcome to the forum @joerahn Smile

Gearbox clunkiness is part of the CB experience. Actually, it's quite normal for this type of gearbox-design to work horribly when handled 'too carefully'.

The thing is - it's a dog-box. Please start by searching the internet for an explanation on what this is. You will find a technical explanation and discover that eg. rally-cars use them too, because they are fast. The reason for putting a dog-box in the CB is not only to get at the quick shifting, but also because it is small.

In stead of the traditional synchromesh-mechanism aligning sprocket speeds on shift, there's - nothing. Just big, fat interlock splines designed to take the 'klonk' on shift. Sounds like a bad thing but it works great; actually it works better the faster you go.

So, with dog-boxes there's a trick to learn; clutchless shifting...
Yup, that's right. No clutch on shift. It takes some practice to master, but the reward is an almost unbroken pull up through the (upper) gears.
Works best upwards on 3-4, 4-5 and 5-6 transitions with revs on or above 6k.
You simply ease off the throttle while applying a somewhat decisive push upwards with your toe on the pedal. Click. Then back on the throttle.
Shift is initiated with the throttle, not by pushing harder on the lever.
Done right, it works klonk-less, lightning-fast and without any effort on your part.
You will wonder why everyone isn't doing it this way - it's so natural.

There is one thing to watch out for: false neutrals! Once in a while the box will miss the gear and since you're all focused on getting  back on the throttle, you will end up sending the revcounter sky-high... Usually I do this overtaking annoying old ladies  in slow-moving cars. And every single time I end up scaring them - and myself - in the process.

Happy riding Smile
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skyrider
the 900
the 900

Posts : 1955
Location : preston lancs

Re: Rattling gearbox

Post by skyrider on Fri 22 Apr 2016, 8:58 pm

yes clutchless changes are sound I do it all the time you will get used to doing it Smile

dado_dassler
Barry Sheene
Barry Sheene

Posts : 82

Re: Rattling gearbox

Post by dado_dassler on Fri 22 Apr 2016, 9:01 pm

@joerahn wrote:I used forum search on my problem but since my english skills is fairly poor i didnt got much of it.

just a few weeks after buying my bike i had the same paranoid problem, but apparently it's completely normal if you go easy on the gear lever.
a solid shift is what you need as people have already mentioned, but i have also heard that using semi synthetic oil in these older bikes instead of fully synthetic helps reduce the noise when shifting gears, though i have not tested this yet.
here is a link to my post (there is video and sound too): clutch or transmission issue?
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joerahn
Newbie
Newbie

Posts : 2
Location : Moscow

Re: Rattling gearbox

Post by joerahn on Sun 24 Apr 2016, 4:36 pm

Thank you for your answers, guys.

Though i think you can understand my confusion, because i'm kind of stumbled upon this thing. It was ok when i bought my bike. I checked it thoroughly, even shift through all gears on a central stand and gear change were smooth at the moment. But after few month i got this.

Looks like i'll have to live with it. Smile

I have a question though. Could this eventually lead to a worn off teeth on a second gear?
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jchesshyre
the 900
the 900

Posts : 643
Location : Chester

Re: Rattling gearbox

Post by jchesshyre on Sun 24 Apr 2016, 5:36 pm

If it's got worse then it could be too much slack in the clutch cable (should be 10-20mm measure at the end of the lever) or that the cable's about to snap. I once had difficult gear changes and neutral finding as the warning sign of a cable that shortly afterwards snapped.
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stormbringer
Moderator
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Posts : 1231
Location : Aarhus, Denmark

Re: Rattling gearbox

Post by stormbringer on Tue 26 Apr 2016, 6:42 am

@joerahn wrote:But after few month i got this.

Could this eventually lead to a worn off teeth on a second gear?

I don't like to hear that it's gotten worse. It shouldn't. As jchesshyre says, make sure your clutch cable is sound and well functioning. Clutch cables are known to not last forever - some of us even carry a spare cable under the seat for roadside repairs...

No teeth on the gears are going to be worn off. All the gears are constant mesh - engaging is by mean of 'dogs' on the side of the gearwheel, locking into a carrier wheel with matching dogs. The carrier wheel is moved sideways by a fork (actuated by the gear lever mechanism), locking the gear to the splined axle.

Gearboxes are little mechanical marvels - I urge you to go have a look at functional drawings you can surely find on the 'net. Or, if you are so inclined, go find an old knackered engine and take it apart simply to learn how energy is sent from the pistons through the crank, the gearbox and the final drive to the rear wheel.

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