Rear end noise

[Bud]

Bike on the center stand. Bags off so the bike is resting on the front wheel. Start the engine and engage first gear at idle speed.

 

Clunk, clunk, bang, clunk, clunk, clunk noise from the rear end. When I rev it up, the noise goes away.

 

The rear wheel has rotational play but movemet from side to side.

 

Also, with bike off and out of gear, rotating the rear wheel produces no noise.

 

Took off the band clamp and rolled back the big rubber boot and fluid (appeared to be gear oil) came out? Normal or sign of %$#@*%#@!!!

 

 

Pending rear end failure? Splines? Where do I start?

 

Any and all help appreciated.

[Joe Frickin' Friday]

I have the bike on the center stand. Bags off so the bike is resting on the front wheel. Start the engine and engage first gear at idle speed.

 

Clunk, clunk, bang, clunk, clunk, clunk noise from the rear end. When I rev it up the noise goes away.

 

The rear wheel has rotational play but movemet from side to side.

 

Pending rear end failure? Splines? Where do I start?

 

Took off the band clamp and rolled back the big rubber boot and fluid (appeard to be gear oil) came out? Normal or sing of %$#@*%#@!!!!

 

Any and all help appreciated.

 

If it's from the final drive area, it's probably not the splines. Although there are three spline sets (one at each end of driveshaft and one at front of gearbox), the failure-prone one is at front of gearbox.

 

With engine off and bike on c-stand, does rear wheel spin smoothly by hand? There may be clunk-noises as you reverse direction of rotation (especially if it's in gear), and that's normal lash in the driveline. But if it's got a gravel-like feel to it as you spin it, then you may have impending wheel crown bearing failure. Confirm by draining final drive oil; if it's sparkly and there are palpable chunks (not fine sludge) of metal on the magnetic drain plug, you need to get this fixed before you ride the bike again.

 

OTOH, if the wheel rolls smoothly by hand (and there are no shards of metal present on the magnetic plug when you drain the final drive oil), I'm betting the noise you're hearing is the wheel/driveline responding to instantaneous RPM fluctuations of the engine. That is, engine speeds up on an expansion stroke and gives the wheel a "kick," then the engine slows down on a compression stroke and the speeding wheel bumps up against the other end of the driveline's lash. When you speed up, the RPM fluctutations aren't as large (and final drive oil drag is higher), so the driveline tends to stay at one end of its lash. When you are riding the bike at low speeds, you don't hear the driveline noise because the wheel is held at more or less constant speed by the bike's mass, and the engine's RPM fluctuations are instead absorbed by the driveshaft's rubber coupling and the gearbox's input shaft (which has a torsional shock absorption mechanism built into it).

 

Re: fluid from FD boot: the input shaft seal on the final drive tends to weep on some bikes. It has been attributed in the past to having overfilled the FD slightly, e.g.to the top of the fill hole threads instead of the bottom. It has also been attributed to a nick or burr on the input shaft which eventually causes the seal to leak. In any event, as ugly as the leakage looks, the actual volume usually isn't very much, usually not much more than a tablespoon between maintenance intervals. If you remove the fill plug and check the level, you should find that the level is still pretty high. Once you've satisfied yourself that the FD is not in jeopardy from loss of lubricant, clean things up, put the boot back in place, and seal it on with long zip ties, nice and tight so it doesn't weep oil all over the outside of your FD and make a mess of things.

[Boffin]

There is a lot of play designed into the drivetrain, mostly at the engagement dogs in the gearbox. With the bike in gear and engine off, it should be possible to rotate the rear wheel a couple pf inches back and forward.

 

Now at idle, the engine does not spin at an even speed. With no load on the wheel, it will slap back and fore between the limits of that couple of inches of slop, producing the most horrendous sounding, but benign noises. I would not make a practice of running the bike on the stand, for safety reasons, but if anyone does they will find that TADT.

 

Andy

[Bud]

I have the bike on the center stand. Bags off so the bike is resting on the front wheel. Start the engine and engage first gear at idle speed.

 

Clunk, clunk, bang, clunk, clunk, clunk noise from the rear end. When I rev it up the noise goes away.

 

The rear wheel has rotational play but movemet from side to side.

 

Pending rear end failure? Splines? Where do I start?

 

Took off the band clamp and rolled back the big rubber boot and fluid (appeard to be gear oil) came out? Normal or sing of %$#@*%#@!!!!

 

Any and all help appreciated.

 

If it's from the final drive area, it's probably not the splines. Although there are three spline sets (one at each end of driveshaft and one at front of gearbox), the failure-prone one is at front of gearbox.

 

With engine off and bike on c-stand, does rear wheel spin smoothly by hand? There may be clunk-noises as you reverse direction of rotation (especially if it's in gear), and that's normal lash in the driveline. But if it's got a gravel-like feel to it as you spin it, then you may have impending wheel crown bearing failure. Confirm by draining final drive oil; if it's sparkly and there are palpable chunks (not fine sludge) of metal on the magnetic drain plug, you need to get this fixed before you ride the bike again.

 

OTOH, if the wheel rolls smoothly by hand (and there are no shards of metal present on the magnetic plug when you drain the final drive oil), I'm betting the noise you're hearing is the wheel/driveline responding to instantaneous RPM fluctuations of the engine. That is, engine speeds up on an expansion stroke and gives the wheel a "kick," then the engine slows down on a compression stroke and the speeding wheel bumps up against the other end of the driveline's lash. When you speed up, the RPM fluctutations aren't as large (and final drive oil drag is higher), so the driveline tends to stay at one end of its lash. When you are riding the bike at low speeds, you don't hear the driveline noise because the wheel is held at more or less constant speed by the bike's mass, and the engine's RPM fluctuations are instead absorbed by the driveshaft's rubber coupling and the gearbox's input shaft (which has a torsional shock absorption mechanism built into it).

 

Re: fluid from FD boot: the input shaft seal on the final drive tends to weep on some bikes. It has been attributed in the past to having overfilled the FD slightly, e.g.to the top of the fill hole threads instead of the bottom. It has also been attributed to a nick or burr on the input shaft which eventually causes the seal to leak. In any event, as ugly as the leakage looks, the actual volume usually isn't very much, usually not much more than a tablespoon between maintenance intervals. If you remove the fill plug and check the level, you should find that the level is still pretty high. Once you've satisfied yourself that the FD is not in jeopardy from loss of lubricant, clean things up, put the boot back in place, and seal it on with long zip ties, nice and tight so it doesn't weep oil all over the outside of your FD and make a mess of things.

 

 

Thanks for the quick reply as my heart has been running double time!

 

Drained fluid. No shards or specks of metal!

 

Rolled wheel forwards and back with no noise or any feeling of grinding!

 

Let rest of fluid drain from boot area. You were correct. What at first seemed like a major leak (because I wasn't expecting ANY fluid behind the boot) was about a couple of teaspoons full.

 

Buttoned things back up and going to ride!

 

Thanks for the very prompt advice which was to the point.

 

Gotta love this place.

[Bud]

There is a lot of play designed into the drivetrain, mostly at the engagement dogs in the gearbox. With the bike in gear and engine off, it should be possible to rotate the rear wheel a couple pf inches back and forward.

 

Now at idle, the engine does not spin at an even speed. With no load on the wheel, it will slap back and fore between the limits of that couple of inches of slop, producing the most horrendous sounding, but benign noises. I would not make a practice of running the bike on the stand, for safety reasons, but if anyone does they will find that TADT.

 

Andy

 

Thanks Andy,

 

Here is a pic with marks showing how much the tire moves front to back.

 

[nrp]

The klunking etc is from the overall mechanical system in your driveline that has several points of backlash, being excited by the 1/rev torsional vibration caused by the 2 cylinder engine with a light flywheel. At higher speeds it will go away.

 

Don't worry about it. I'd worry more if it didn't do that

[Ken H.]

Here is a pic with marks showing how much the tire moves front to back.

TADT. Actually your marks indicate a bit less than most.