Help! Strange clunking noise...

Matthew,

I have had the same experience with my freewheel.

You'll find there is a degree of slack in the free wheel bearings allowing the cluster to rock slightly. This will be the knocking sound you're hearing.

I recently renewed my cluster and the noise reappeared. And once again I found the slight rock present.

I tried removing the thinest shim in the freewheel bearing but found the freewheel tended to bind (ie chain suck became a problem) The noise did however disappear.

Cheers Ray

Since your clunk only happens when you are pedalling I suspect it is related to the chainset or chain. Does it occur when back pedalling with the bike stationary ? Does it occur when the pedals are turned forwards slowly with rear wheel off the ground. It could be a stiff link in the chain which can not flex over the jockey wheels properly. Are you sure its from the back end of the bike, could be the Bottom Bracket bearings. Could be something catching on your crank as it revolves such as the end of the front derailleur cable.

Matthew Myatt said:

My ancient MTB has developed an annoying noise

How old is it? Does the wheel have a modern cassette or an old-style screw-on freewheel?

If unsure, see: sheldonbrown.comfree k7.htmlOpen ↗

............

Quoted message said:

However, I'm not convinced the noise is due to the hub bearings and I'd rather not splash out on a
new wheel unless I'm certain this is the cause. Three things that make me question whether the hub
bearings are at fault:

1) Slightly tightening or loosening the bearings has no effect on the noise.
2) The noise only happens when I'm pedalling. I expect that a knackered hub bearing would make a
noise whenever the wheel is tunring, during freewheeling for example.

I would expect so too.

Quoted message said:

3) The noise is considerably worse when I'm using the middle cogs of the freewheel (the ones I
use the most). I can't see how the gear I'm in would effect the problem if it were due to the
hub bearings.

You might happen to apply a different amount of torque or less even torque in those gears.

Quoted message said:

Given these observations, I'm beginning to suspect a knackered bearing inside the freewheel. Is
this possible/likely?

For cassette hub: I would also suspect the freewheel body (often known as the "freehub body" - thing
that cassette goes on) - but it probably won't be its bearings exactly. The ratchet/drive mechanism
could be damaged/broken. It's not economical to repair - so it means a new freewheel body. First
make sure cassette is ok and freewheel body is not loose.

Freewheel hub: I'm not sure, sorry.

~PB

"Pete Biggs" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Matthew Myatt said:

My ancient MTB has developed an annoying noise

How old is it? Does the wheel have a modern cassette or an old-style screw-on freewheel?

Probably over ten years now. The frame's as rusty as hell and doesn't have much paint left on it,
but I've upgraded most components as they've worn out. It rides pretty nicely, considering it's
age and weight, and the crappy frame makes it pretty unattractive to thieves. Ideal as a
hack/commuting bike.

Anyway, just to confirm: it's an old-style hub that takes a screw-on freewheel. So, unfortunately,
your advice doesn't count. Thanks for trying, though - much appreciated.

Mat

MSeries said:

Since your clunk only happens when you are pedalling I suspect it is related to the chainset
or chain.

I don't because it's one clunk per wheel revolution - not crank or chain rev.

~PB

"zathras" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

Matthew,

I have had the same experience with my freewheel.

You'll find there is a degree of slack in the free wheel bearings allowing the cluster to rock
slightly. This will be the knocking sound you're hearing.

Thanks for the response. Could you actually feel the slack by rocking the freewheel? I'll give mine
a wiggle later (as it were) and see if there's any give.

Quoted message said:

I recently renewed my cluster and the noise reappeared. And once again I found the slight rock
present.

I'd have thought buying a new freewheel would solve the problem - were you just unlucky, or could
there be some other problem with the rear wheel / transmission that causes the freewheel bearings to
wear prematurely?

Quoted message said:

I tried removing the thinest shim in the freewheel bearing but found the freewheel tended to bind
(ie chain suck became a problem) The noise did however disappear.

Woah - I don't fancy taking the freewheel apart! From what I've heard, that path can lead to many
hours hunting around the floor for little springs and ball bearings and hours more fun trying to fit
them back together again.

I'll see if I can borrow an old freewheel to see if that cures the problem. (I realise the chain'll
probably skip, but I'll hopefully be able to ride it enough to see if the noise has disappeared.)

Thanks very much for your help,

Mat

"MSeries" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

Since your clunk only happens when you are pedalling I suspect it is related to the chainset or
chain. Does it occur when back pedalling with the bike stationary ? Does it occur when the pedals
are turned forwards slowly with rear wheel off the ground. It could be a stiff link in the chain
which can not flex over the jockey wheels properly. Are you sure its from the back end of the
bike, could be the Bottom Bracket bearings. Could be something catching on your crank as it
revolves such as the end of the front derailleur cable.

Thanks for the advice. I'm pretty confident it is something wrong with the back wheel / freewheel
because the 'clunk' happens once every revolution of the back wheel. This effectively rules out the
chainset / chain / bottom bracket. It's *definitely* not a stiff chain link as I've checked for this
(before I realised the once per wheel revolution thing).

The noise only occurs while pedalling on the bike (Murphy's law of bike maintenance) and doesn't
happen while backpedalling.

The only other explanation I can come up with is a dodgy spoke. It is possible that this would cause
a noise only when pedalling because of the extra force on the spoles when the wheel is being driven,
but it seems unlikely and there aren't any obviously loose or damaged spokes. And it feels more like
a hub thing (can feel the clunk through the bike frame).

I'm liking zathras' idea that the freewheel bearing is shot. I'll check this tonight and post my
findings...

Thanks again,

Mat