Mysterious rear wheel thumping

[baz666]

I've looked through old posts but can't find anything that applies.
I get a strange rear wheel thumping. Maybe once per second. I'm not sure I don't think it's every revolution of the wheel since the thumping doesn't speed up when I go faster. It stays pretty much the same at any speed. Maybe at highway speeds it's thumping faster but I just can't hear it or feel it because of the wind noise, louder engine, etc.
I raised the rear wheel off the ground and turned it back and forth, etc but felt nothing. It's not like a suspension thumping and the bike tracks straight, no rear end vibration.
One mechanic told there might be a flat spot on the tire but another mechanic said that would produced such a pronounced thumping. Neither had time to take it out for a test ride and experience it themselves.
The yellow dot on the tire is not lined up with the air valve. It's actually directly opposite the valve but I've been told that some mechanics prefer to do it that way for some reason.
Could it be the rear wheel bearings? But if it was that, wouldn't the bike vibrate or wobble?
I'm really stumped.
Any suggestions at all would be greatly appreciated.
thanks,
baz

[tkent02]

Chain or shaft drive?

[chef1366]

The fact it stays the same at different speeds is a mystery.

[André]

What bike,chain or shaft?

[Turtleface]

His profile says he has a 750ES. My bike did something similar when my chain bit the dust.

[tkent02]

Yeah, but it should change with road speed if it's a chain problem.

[Turtleface]

Yeah, but it should change with road speed if it's a chain problem.

That's a good point. Last night of my overnight shift, my mind's a bit buggy at the moment.

What part on a 1983 750 ES could possibly move enough to cause a "thump" sensation, but stays at a constant rate regardless of engine RPM or road speed?

If the bearings haven't been checked, is that possible? Obviously, you'd check all the suspension/wheel related nuts and bolts, for correct torque. How old is the tire that's on it? What condition are the roads you're riding on?

[TheCafeKid]

Im betting its either a bad chain a bad sprocket or the CS sprocket nut is loose. One link, if stiff, or corroded or a bad sprocket tooth (twisted, hooked, raised) isnt going to change THAT MUCH with speed, because it will only be felt when the chain link is engaged with the sprocket, and same with a sprocket tooth. If its the chain, you're probably only going to feel it every revolution of the chain, and only when its binding on a tooth. I had this problem on my 1100E. Id switched to a 530 chain and the CS sprocket i had been sold was JUST slightly too narrow. The nut wouldnt tighten down apparently enough to keep it from wobbling (i only found this out later, when replacing the whole shabang, and switching to a larger CS sprocket) If the sprocket will walk in the CS, even as little as a mm or two, it is going to bind the chain, killing the chain quicker, etc.. CHeck those thing.. Id replace the chain and sprockets anyway, as if the nut or a tooth is bad, the chain is toast..

[baz666]

Sorry, it's chain drive. '83 GS750ESD
530 - 43, I believe.
The tires both have less than a 500 kms on them (300 mi.), though they are Kenda Challengers, not the best tires out there.
The shock is just under a year old, I have the bill.
The chain, I don't know. It looks very clean and I can't see any binding or bent links. I have to take off the Cam Shaft sprocket cover to take a look at it s condition and check the nut's torque.
thanks,
baz

[posplayr]

with a freinds help of course, I would put it on a centerstand or rear wheel stand and running the rear wheel up to about 3K in 5th gear. That should help isolate the problem which is likely the chain.

Keep your fingers away rom the chain.

[baz666]

Well, I found the source of the mysterious rear wheel thumping.
Actually, it's really more of a rubbing sound.
It happens every rotation of the rear wheel. For some reason, I decided to take out the rear brake pads (probably because it's easy to do) and ride the bike up and down our dead end street like that to see if it made a difference.
I took out the rear pads and yep, no more thumping/rubbing. The pads have worn down enough that there is a lip about 1/4" high at the top of the pad material. (Funny because there lots of pad material left.) I'm not sure if the disc rubs against that lip or what.
The thing I'm not certain about is whether the problem is the pads or whether the disc itself is perhaps warped. But then wouldn't I see one pad being more worn down than the other? Currently, they are both equally worn down.
I'm picking up a set of new Ferrodo pads today so I'll find out.
If it still thumps away once the new pads are in, I guess I have to look at the disc. Does anyone know what other components would rub against the rear pads?
thanks,
baz

[Jagir]

i am experiencing a similar problem after having my front shoes 're-shod' on my old Honda moped. After 'wearing them in' (riding 20 km and braking a bunch) the sound has dissipated a bit.