Help! Strange clunking noise...

My ancient MTB has developed an annoying noise that I'm trying to diagnose.
If anyone has any ideas, or has had a similar problem in the past, I'd be
very grateful for your advice...

There is a loud 'CLUNK' (or occasionally 'CLUNK-clunk') coming from the back
wheel once every wheel revolution. It sounds and feels very much like a
knackered bearing. Indeed, I took the hub (old style 7-speed freewheel
sort, not freehub) apart to clean and reset the bearings and the race on the
RHS of the hub is fairly worn, but without any particularly nasty dints.
The ball bearings themselves look fine.

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.
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.

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

Thanks for any help - it'll be much appreciated,

Mat

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



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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.



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Matthew Myatt wrote:

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: http://www.sheldonbrown.com/free-k7.html

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

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.

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

"zathras" wrote in message
...
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.

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?

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