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Gearbox 'Clunk' while in gear

3K views 13 replies 9 participants last post by  ssevy 
#1 ·
Recently I've noticed the Legend gearbox occasionally making a 'clunk' noise, very similar to the sound it makes when I put it in first, while I'm in gear and riding. Seems to happen most often after I've shifted from 1st in 2nd. Doesn't have any noticible effect on the motor or handling of the bike... just sounds like it's dropped back into 1st on its own, which is a bit unnerving.

Anyone else had this happen? Any ideas what might be causing it?

I also *may* (see other post) have an alternator bolt issue - could this be a contributor? Could the alternator issue lead to, say, a plug not firing, and the engine disengaging briefly - so the 'clunk' would be the engine re-engaging? No idea if that's even feasible, shooting in the dark here.

Any feedback appreciated, thanks.

cheers,

~crosstie
 
#2 ·
Hi Crosstie,
Sorry to hear about your problem, not sure what to make of the 'clunk' (doesn't sound good tho') but can't imagine how an alternator an could cause a misfire - at least until the battery runs down. My old Tbird had the alternator shaft bolt head shear but it didn't 'clunk', just rattle. Maybe you should pull the alternator to have a look see? Recommend you use an impact driver & good quality bit from the off on those torx bolts - very easy to strip the heads.

Mike
 
#3 ·
The engine dropping from 2nd to 1st would be unmistakeable, so it seems unlikely. If it was dropping out of gear it would be more likely to drop into neutral.

An alternator bolt issue would not cause a misfire. The battery would act as a reserve of power.

It's a long shot, but I would check the engine sprocket to make sure it is tight.
 
#4 ·
Thanks for the replies.

The bike is definitely not dropping out of gear - pretty sure I'd notice that :) It just sounds like it.

It only did it once today (as opposed to a couple times yesterday), and it was while I was idling in neutral at a stoplight. I'm starting to wonder if it's something physically moving on the bike (as opposed to inside the engine)... carbs 'shifting' or something. Keep an eye on it I guess... yikes!
 
#5 ·
I'm just curious here, but does it feel like it's coming most heavily through the side panels (silver bits, with '900' on 'em)? I've had something like that, and it seemed to be tied to a coil not being happy (in the rain, as it happened) - when dry, I don't get it, and it only shows up when that coil acts up after a nice long soak in the rain.
 
#7 ·
Recently I've noticed the Legend gearbox occasionally making a 'clunk' noise, very similar to the sound it makes when I put it in first, while I'm in gear and riding. Seems to happen most often after I've shifted from 1st in 2nd. Doesn't have any noticible effect on the motor or handling of the bike... just sounds like it's dropped back into 1st on its own, which is a bit unnerving.
If it's not actually changing gear (just clunking) then the first thing I'd look at is the chain and sprockets.

If you've got too much slack or badly worn parts the chain may be jumping teeth on a sprocket.

Also check the chain guide on the swing arm. It may be coming apart.


Jim
 
#9 ·
Thanks for the suggestions all.

Shoggot, it *could* be coming from that general area but it's not that distinct... and mike bike hasn't been really wet recently, it's been beautiful here lately.

Slinky - thanks, I'll check the plugs... doesn't seem loud enough for a carb backfire though (guessing, never to my knowledge heard that happen before).

JimmyJ900 / Petrol - thanks as well, I'll check my chain tension and wear. Does 12K miles seem like a lot on a chain? I wax it pretty consistently.

JimmyJ900, is chain guide = chain guard? I drilled some holes in mine, but other then that it seems pretty solid.

cheers,

~crosstie
 
#10 ·
Mileage isn't necessarily a good guide to chain condition since chains wear unevenly. It only takes one bad bounce with the chain adjusted too tight to cause a badly stretched section.

12K miles is also getting close to change time. 15K to 20K seems to be about the limit for the stock chain.

You need to get the back wheel off the ground and turn the rear wheel in the normal direction of travel and watch for loose and tight spots. (It takes several revolutions of the wheel to cover all the combinations of chain and sprocket.)

Everybody says to set the chain tension on the tightest section, but how loose then is the loosest section?:confused:

Also... The chain guide is that funky rubber thing that bolts to the front section of the swingarm between the chain and swingarm itself.

Jim
 
#11 ·
Checked the chain tension today, it's a bit loose across the chain (~40mm) so I'll get that adjusted. The chain guide looks to be in ok shape to me.

Not sure about chain wear, nothing looked obviously wrong but I haven't checked it for stretch.

The rear sprocket is a bit worn but none of the teeth seem that rounded to me. Do you really have to drain the oil to take the front sprocket cover off? Seems like an odd design. Will look at that when I get a chance.

Also noticed I'm way low on coolant - guess I'm not going to get much riding in this week...

cheers,

~crosstie
 
#12 ·
You don't need to drain the oil to remove the front sprocket cover, just so long as the bike is upright you will only get a few mls of dribble out of it. Check that front sprocket mate, I had one that a bike shop had left a bit loose, luckily it didnt bugger the splines on the countershaft, but there is the potential for that to happen. I only noticed a little driveline snatch when the chain was almost worn out. But it may manifest itself in other ways. I'm a bit deaf too, been working around noisy machinery too long and my TBird is rather loud.
 
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