Mystery sound - scientific progress goes "clonk?"

[j-p.s]

(I have a funny noise in my bike. I should start by mentioning that a
decent LBS has had a look over it and found nothing, but see at the end.)

My chain and cogs go clonk. I have a newish (four months) hybrid, kept in
reasonable nick and cleaned a month or so ago. The clonk is similar in
sound to that when you engage the pedals suddenly: a muffled metallic
thud.

It doesn't really transmit as vibration into the pedals, and it's
repetitive with the approximate period of revolution of the back wheel
(really the back cassette, I suppose, as when freewheeling there's
nothing).

What's bizarre is that it tends to go away when cycling downhill. This
isn't a pressure on pedals thing: small pressure uphill gives quiet
clunks; medium pressure downhill gives nothing. This intermittent nature
may have foxed the LBS, as I cycled gently downhill to them.

Any ideas, or ideas how I might diagnose? I would live with it but it
sounds worrying, like money emptying itself from my bank account.

J-P
--
He is a Man with Too Much Salt, like an Mormon on a Corner.

[Pete Biggs]

j-p.s wrote:
> (I have a funny noise in my bike. I should start by mentioning that a
> decent LBS has had a look over it and found nothing, but see at the
> end.)
>
> My chain and cogs go clonk. I have a newish (four months) hybrid,
> kept in reasonable nick and cleaned a month or so ago. The clonk is
> similar in sound to that when you engage the pedals suddenly: a
> muffled metallic thud.
>
> It doesn't really transmit as vibration into the pedals, and it's
> repetitive with the approximate period of revolution of the back wheel
> (really the back cassette, I suppose, as when freewheeling there's
> nothing).
>
> What's bizarre is that it tends to go away when cycling downhill. This
> isn't a pressure on pedals thing: small pressure uphill gives quiet
> clunks; medium pressure downhill gives nothing. This intermittent
> nature may have foxed the LBS, as I cycled gently downhill to them.

I suspect it is pressure related even though you think only "small"
pressure uphill makes the noise. The pressure is probably less evenly
applied there at least.

Could be a faulty freewheel mechanism: frewheel body (hub part that
cassette fits onto) may need replacing. These can make odd, unique and
disturbing noises! If it is this, it will eventually fail altogether,
meaning you won't be able to freewheel.

Check wheels and tyres aren't fouling anything (allowing 2mm for flex).
If it was in time with crank revolution, I would suspect the cranks or
bottom bracket. Chain revolution: stiff link.

> Any ideas, or ideas how I might diagnose? I would live with it but it
> sounds worrying, like money emptying itself from my bank account.

Could you get another cyclist-who-knows-about-these-things or someone from
LBS* to ride alongside and behind you? They may be able to pin-point the
sound more clearly than you can from the saddle - and also watch for
anything wobbling!

* Alternatively, leave bike at shop and request they take it out for a
proper test ride until they experience the problem for themselves.

~PB

[Colin]

j-p.s wrote:
> (I have a funny noise in my bike. I should start by mentioning that a
> decent LBS has had a look over it and found nothing, but see at the
> end.)

Check your pockets. I recently had a worrying "chink" on every turn of the
pedals: turned out to be the house key and some change striking each other.
:-)

Colin
--
cycling AT spiralpathways DOT co DOT uk

[j-p.s]

On Tue, 22 Jul 2003 16:44:35 +0100, Pete Biggs scrawled:
) Could be a faulty freewheel mechanism: frewheel body (hub part that
) cassette fits onto) may need replacing. These can make odd, unique and
) disturbing noises! If it is this, it will eventually fail altogether,
) meaning you won't be able to freewheel.

See, this is what I thought it was, and left it with the LBS. They
reported nothing, and I had to agree that there was no noise in the 200
yards prior to reaching the LBS....

This morning by the time I got out to Sandford-on-Thames I was making a
noise fit to frighten children. I stopped and wiggled everything I could
(on my bike, that is). Found it: the rear wheel cassette was hypermobile
and could be translated along its axis by about three millimetres or more.

By the time I had got to the LBS, it was much quieter and could only move
a half a millimetre. But it was under warranty and they agreed it needed
replacing for free. After four months that shouldn't happen, and they're
returning it to Giant. It's now sorted and noiseless, and they put a new
chain on too, obverously.

.... A very odd noise. Like having three or four (or three-and-a-half)
spokey-dokeys on my wheel. I'll remember that one, as did you :) The
relapses and remissions of it confused me no end, though.

J-P
--
"But we make his love too narrow/ with false limits of our own,/ and we
magnify his strictness/ with a zeal he will not own."

[j-p.s]

On Tue, 22 Jul 2003 19:15:57 +0100, Colin scrawled:
) Check your pockets. I recently had a worrying "chink" on every turn of the
) pedals: turned out to be the house key and some change striking each other.

Like Henry Braun said to me off-list, the number of clanks and bonks that
are a result of mudguards and brake cable ends is ridiculous. If I had a
penny for every time... well, I'd have enough for a can of Vimto, anyway.

J-P
--
Perhaps electricians use these labels as curses to ward away amateur
competition. But all the same, I shall resist the temptation to do any
wiring until I am completely sober.

[Dave Kahn]

On Wed, 23 Jul 2003 09:10:56 +0000 (UTC), "j-p.s"
> wrote:

>On Tue, 22 Jul 2003 19:15:57 +0100, Colin scrawled:
>) Check your pockets. I recently had a worrying "chink" on every turn of the
>) pedals: turned out to be the house key and some change striking each other.
>
>Like Henry Braun said to me off-list, the number of clanks and bonks that
>are a result of mudguards and brake cable ends is ridiculous. If I had a
>penny for every time... well, I'd have enough for a can of Vimto, anyway.

A few months ago I was hearing a very delicate little chink-chink
sound on my Sigma that occurred on some rides but not others. I
couldn't tell where it was from and it was driving me mad. It was only
when the same sound happened on the Super Galaxy that I realised it
the chinks were coming from me. It turned out that when I wear a
particular jacket over a particular jersey the tag of the jersey zip
dangles over the tag of the jacket zip and bounces on it.

--
Dave...

[Peter Connolly]

> Check your pockets. I recently had a worrying "chink" on every turn of the
> pedals: turned out to be the house key and some change striking each
other.
> :-)

I find it a good idea to keep some loose nuts and bolts in a tobacco case in
your panniers. You'll never hear any minor noises then!

Pete.