Topic: Rhythmic thump on decel at lower speed

[Dunk]

I noticed today my '75 CB750 had a rhythmic thump at low load to decel at 25-30 MPH. Almost like the rear wheel is out of round. I first noticed this immediately after changing he rear tire a few months ago (BT46), during which I cleaned the chain with Oring chain cleaner and lubed. Was going to pull the rear wheel and inspect but it went away and has been normal for months. Today was our first really cold day here, 30* this morning and high around 36*. I noticed this thump, almost like a bead not seated perfect all the way around but only at 25-30 MPH and most prominently under light decel at idle throttle. I do not feel it in the brake pedal slightly pressing but not applying the rear brake, and the thump feel continues regardless of applying the rear brake.

I put the bike on center stand after riding home and spun the rear wheel each direction. I did not notice any oddities or stiffness in the chain. Not sure what's going on, presumably either chain or wheel bearing issues but I can't feel either on center stand. I guess I have to pull the rear wheel and chain for better inspection but anyone have thoughts on this? Odd that it would go away quickly (thought maybe bead not seated 100% and sorted itself out within a few miles), but come back in cold weather. Or maybe a coincidence.

[kerryb]

That's about the same conditions for head shake on my 83 wing.  I suggest you check tire pressure and tread wear to see if it changes any.  Also check tire balance if you can.

[Don R]

 Watch the chain as you rotate the tire to see if it has a tight spot. Also, someone here had a loose front sprocket recently although that would make a faster thump than a bad tire might.

[HondaMan]

Look closely at the chain's master link, if it has one(?). If the clip came off, the sideplate could be trying to work itself off, which will be most noticed as a 'tick' or 'thump' at low [chain] torque moments when entering the sprocket(s).

[Tracksnblades1]

Are you in 5th gear…?

Did you repack the rear wheel bearings..?

Have you tried the same deceleration in other gears, to verify it’s not the transmission? Like faster or slower thumps at the same mph..

Will it continue to thump with the clutch pulled in..?

[newday777]

I noticed today my '75 CB750 had a rhythmic thump at low load to decel at 25-30 MPH. Almost like the rear wheel is out of round. I first noticed this immediately after changing he rear tire a few months ago (BT46), during which I cleaned the chain with Oring chain cleaner and lubed. Was going to pull the rear wheel and inspect but it went away and has been normal for months. Today was our first really cold day here, 30* this morning and high around 36*. I noticed this thump, almost like a bead not seated perfect all the way around but only at 25-30 MPH and most prominently under light decel at idle throttle. I do not feel it in the brake pedal slightly pressing but not applying the rear brake, and the thump feel continues regardless of applying the rear brake.

I put the bike on center stand after riding home and spun the rear wheel each direction. I did not notice any oddities or stiffness in the chain. Not sure what's going on, presumably either chain or wheel bearing issues but I can't feel either on center stand. I guess I have to pull the rear wheel and chain for better inspection but anyone have thoughts on this? Odd that it would go away quickly (thought maybe bead not seated 100% and sorted itself out within a few miles), but come back in cold weather. Or maybe a coincidence.

Is this an old chain or a new chain?
When you cleaned the chain did you use a grunge brush to help clean it?
Have you removed the chain and inspected it for one or more stiff links? That is where I'd start, that and pull the wheels off and stick your finger in each wheel bearing and inspect for notches(rotate finger as you put pressure on the bearing)

[MauiK3]

I'm voting for chain as well.

[rotortiller]

I first noticed this immediately after changing the rear tire a few months ago (BT46),

That's where I would start, maybe a bad belt you cannot see but feel driving it, especially since you checked the chain out already. Try farting around with the tire pressure to see if it makes a difference.

[jgger]

Could it be in the cush drive rubbers in the rear wheel? Perhaps the rubber being hardened because of temperature.  This is only a guess and I didn't sleep at a Holiday Inn last night 🙃.

[BallAquatics]

.....This is only a guess and I didn't sleep at a Holiday Inn last night 🙃.

[BenelliSEI]

Next time you have the rear wheel in the air, over inflate the new tire and have a close look. Any chance something has let go in the basic tire construction? See any lumps or bumps? Also let out all the air and check again. Something may become more obvious at the two extremes.

P.S. I assume the tire was mounted in the correct rotation direction?

[Nurse Julie]

Sounds like a seized link on the chain.

[Don R]

 We're going to keep guessing until you tell us what it was! L0L! My double disc conversion had a weird noise when I spun it, it was the tire tread rubbing on the wheel clamp on the lift.

[newday777]

So Dunk, no reply from you to questions asked of you....
I'm guessing that you didn't hit the notify button??

[grcamna2]

I'm voting for chain as well.

I'm also thinking chain/sprockets.

[rotortiller]

Chain binding is more like a clicking, sounds almost like a chipped gear and has been mistaken as such. There is a notable tonal difference, just like there is with dry and wet farts. lol  Then again maybe the rider needs music lessons.

[BenelliSEI]

Certainly curious!

[Deltarider]

I say... that's a very, very convincing wet fart.

[Jerry Rxman Griffin aka MuthaF'er]

Isn't that called a shart?

[rotortiller]

Isn't that called a shart?

With a bubbler I would have to agree somewhat, however without 'solid' evidence there is no real way of knowing or measuring the airborne particle density or even skid quality from a sound byte.