Kawasaki Vulcan Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
250 Posts
Discussion Starter #1 (Edited)
From about 18 to 25mph I get a rubbing sound. It sounds sort of like when you blow into an empty beer bottle just right. For a while I've thought one of the brake discs were warped and, when traveling at that narrow speed range, the rubbing was at a frequency that produced the sound that I could hear. I can't really tell if it's coming from the front or back. I've tried maintaining a steady 20mph speed with only front or back brake applied to see if I could figure it out but it didn't make enough difference to confidently say it was the discs much less front or back. The sound is present at that speed when slowly accelerating, decelerating, in a straight line or curve. Today I got the bike jacked up and checked the discs for warpage deflection with a dial gauge. All 3 discs were within manual specs. I checked belt tightness per the manual and all is good to go. It is definetely an "in-motion only" noise.

It's an '08 LT completely stock and bought 6 months ago with 16k on the odo. The bike was in amazing condition, cleaner that showroom. The PO had all the shop receipts for routine maintenance. I've put 2k on the bike. It has made this sound since I've been riding it. The bike is rock solid but I'm curious if anyone has had similar noises or thoughts on this.
 

·
Bike Of The Year Winner, 2012
Joined
·
4,905 Posts
While the bike is on the jack, there is no real risk in starting the bike up. Just make sure your tide down nice and tight.

I've done that many times.

Normally I keep the kickstand down, but if I know I'm going to be starting the bike and putting it in gear, I'll have the kickstand up.

Side Note - unless I'm taking the front wheel off, i usually have the jack more towards the rear of the bike. This will bring the back wheel up, while still leaving the front on the ground. Makes everything a bit more stable.

So, crank it up and see if you can identify the noise.
 

·
Registered
Joined
·
250 Posts
Discussion Starter #5 (Edited)
How many miles on the tires? Does it do it in first only or second and third also?
In my neighborhood there are many stops signs mixed in with lots of 35mph speed limits and multiple 15mph curves. So a common routine would be at a stop sign then accelerating normally up to 35-40mph and 3rd gear, maybe a little bit of 4th when there's no traffic. Then slowing down and dropping into 2nd for a 15mph curve followed by another straight stretch and a stop sign. Then repeat this again another 4-5 times. I do this each time I leave home and come back home. When accelerating normally from a stop my speedo arm will sweep across this 18-25mph range probably in second gear. When coming up on the curves I sweep through the 18-25mph range decelerating in 3rd, drop into second at about 15mph and follow the curve. On the backside of the curve I sweep through that mph range while accelerating thru 2nd gear and then to 3rd. When approaching stop signs I'm usually doing about 35-40mph and again sweep down through this mph range. Usually I'll pull the clutch in around 25mph and just before I put my feet down at maybe 1-2 mph I'll pop it into 1st. So engine-wise it happens accelerating with load in 2nd, decelerating in 3rd with some engine braking and coasting with the clutch pulled in and engine at idle rpms.

In all of these conditions, I'll get the same sound between 18-25mph. If I ride at a steady 21-22mph I can get it to make the noise consistently and pretty much remains making the noise until get over 25 or under 18. It does it when the bike is warmed up 5 minutes in the garage and I hit the road and it did it on multiple 3-5 hour trips riding two when I hit that mph zone after both long highway riding and mountain riding with continuous hills, curves and a lot of braking. So heat and passenger-no passenger didn't change it. It never gets worse but it never goes away. It's simply a dependably recurrent rubbing noise between 18-25mph. It's not loud at all but noticeable with a half helmet. Somebody standing 25 feet away probably wouldn't hear it. Again, during the 2000 miles I've ridden it, it's always done that. Otherwise there are no other abnormal noises under any operating conditions.

I've replaced the air filter but otherwise have examined the intake. I understand there are two sets of actuated TB butterflies. Is there a possibility, considering the scenarios described above, that the secondary butterfly actuation is making some noise? I wouldn't imagine they would respond the same, at 18-25mph, with acceleration, deceleration and coasting. Just thinking out loud.

I'm still suspecting something with the disc brakes. Braking is super smooth. There's no herky-jerky when coming to a stop. I'm wondering if the discs and these particular pads simply make this noise at a specific, narrow range of wheel revolutions. I think about how you can rub your finger around the top of a wine glass. If you rub it at the right speed, or frequency, you can create an audible tone from the glass. Rubbing that same glass at a different speed will still introduce all of the same physical effects on the wine glass and probably still vibrates but doesn't generate what we would recognize as a sound. Or like wind blowing across power lines just right will create a sound.

I'll try Smedlin's tip to see if I can rule out the tranny and drivetrain as the culprit. Then I'll check axle torques, disc bolt torques and possibly changing brake pad brand.
 

·
Registered
Joined
·
408 Posts
I've been doing some hands on research regarding the pre-throttles as my bike has a nasty off idle hesitation when cold. Assuming everything you have on the intake side is stock, I doubt the noise is coming from the intake. The only noticeable noise I've heard from the intake minus the air sucking sound at full throttle is the stepper motor going through its homing/calibration sequence at startup. I asked about the mileage of the tires because mine makes a noise similar to what you have described, only at higher speeds and more pronounced in turns, due to very slight front tire cupping. Given that you can make the sound happen consistently I doubt it's the tire. Keep us posted on what you find, these machines are full of all kinds of weird noises.
 

·
Registered
Joined
·
228 Posts
sounds like something is slightly off balance and you are hitting the resonance frequency around 21 mph. Is there any strong vibration or trembling. As Smedlin suggested try running it on the jack and see if it does it. It has to be on the down stream of the clutch otherwise you would here it more often as you pass thought the same RPM range in each gear.

Things to check:
Tightness of your rear hex crown nut on your shaft. (should be nice and tight, if not your spacers might be spinning)
Lubrication of the rubber isolation dampers inside your rear drive hub. (they could be making noises if they are dry rubbing.)
front or rear wheel bearings
tires balanced (could always try throwing a weight on them to just see what happens.
 

·
Registered
Joined
·
2,967 Posts
I had a weird rubbing/scraping noise one time, ended up being a small stick had gotten up beside the belt, mostly behind the shield so it was very hard to see.
 

·
Registered
Joined
·
250 Posts
Discussion Starter #10
Thanks for all the input. I got the bike up on the jack. As you all probably know, with the common jack that most of us has seen there is only about a 3/8" extra on each side of the frame when centered under the bike. I got it up, started it and ran in first for a few moments but didn't feel real comfortable doing it. I'll repeat it again when I can get the bike up, stable and comfortable with running the back wheel up to 30mph.

I didn't run it long and didn't get it up to the 18-25mph range but for the little bit I did I didn't hear anything abnormal.
 

·
Registered
Joined
·
250 Posts
Discussion Starter #11
I think I found the source of the humming sound coming from the left side of the bike when at 18-25 mph, both accelerating and slowing down. For a while I thought it was a slightly warped rear brake disc.

I see now that my front pulley outside lip (the ring that looks like it keeps the belt from coming off the pulley) has a high spot meaning there's a slight inward bend. Then it's wavy for about two more inches. You can barely see it in the pics. It's more obvious in person.



I guess at a certain narrow pulley rpm the belt would resonate like a guitar string.
 

·
wocka, wocka, wocka
Joined
·
5,618 Posts
I think I found the source of the humming sound coming from the left side of the bike when at 18-25 mph,
I guess at a certain narrow pulley rpm the belt would resonate like a guitar string.
does it pick up as you increase speed and drop off when you slow down?
is it only in that narrow band? can you identify a particular melody or what key it is in? if you go faster then slower, can you make it play music?
you mite get a ticket, but try 'splainin to the cop you was just hammerin out a new skore.. hell, IDK, yor the one with the musical bike.. poncho
 

·
Registered
Joined
·
250 Posts
Discussion Starter #13 (Edited)
In accelerating normally, the hum sound comes when the speedo is sweeping through the 18-25mph range, goes away as I continue to accelerate. When faster than that, say on a straight and approaching a curve, as my speed drops while in gear and speedo sweeps thru the 25-18 mph the sound comes, goes away once below 18mph. It is very reliable. Happens every time. Ive gone through that range so many times trying to figure out what it was. Upright or leaned makes no difference. No brakes and riding front then rear brakes makes no difference. It's not a bothersome noise. It's just loud enough for me and passenger to hear with with 1/2 helmets. The sound has stayed consistent in volume, characteristics and about where it happens for several months now. During that time I the belt always had correct tension. Never realigned belt. All three discs are true. Bearings are fine. It's always sounded like a low hum. Sound comes from somewhere between just behind my lower left leg the the back wheel. I've put the bike on the jack and ran it up to maybe 10mph on the speedo. Never felt comfortable going higher with that narrow jack. With no engine noise today, I was able to spin the rear tire by hand and seemed to detect the faintest rubbing sound from the front pulley.

I'll know soon if it is the cause of the hum.
 

·
Registered
Joined
·
361 Posts
DJ, sounds alot like brake pad drag to me.

My old 98 LC1500 suzie used to do it on the front brake. Was only just touching but at certain low speeds could be clearly heard. Like certain low speeds set up a resonance effect exaserbating the noise. Took me a while to figure it out via forum help. Turned out to be a trait with those bikes.

You may have a similar issue here??? Have you tried raising a wheel and spun it to hear if there is any pad drag? will only be oh so slight but detectable.

Cheers Ando
 

·
Registered
Joined
·
64 Posts
My 1500 makes a similar noise around the same speeds. I found mine and it was the front brake rotor/pad contact. Since the rotor is drilled the noise comes from the air going through the holes in the rotor. Apply your front brake and see if noise changes while accelerating to keep same speed. Just a thought.
 

·
Registered
Joined
·
250 Posts
Discussion Starter #16
The rear brake and belt have always been my suspicions. I don't know if I've done enough to rule out the rear brake. I didn't detect any rubbing points when spinning the rear tire freely. I've checked the outside of the rear disc with a runout gauge, but not the inside of the disk. The outside was true. Same for the front brake discs. Cruising while slightly riding the rear brake has made any changes in the sound. I didn't check for runout on the rear pulley. But visually checking while spinning the wheel I didn't see anything obvious, certainly not as obvious as what I saw when watching the front pulley spin. Regardless, I'll know in about a week when I got her all put back together.
 
1 - 16 of 16 Posts
Top