Gears change automatically!

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

Quoted message said:

[Apologies for non-technical terms used]

The chain on my bike keeps jumping down a gear
automatically. That is to say, it seems to want
to be on a smaller back-cog than I set it on.

There doesn't seem to be any particular pattern
to this, it can happen at any time, and in any
gear, and seems to be happening quite frequently
and started this behaviour all of a sudden.

It is quite a problem when going up a hill and
the bike jumps onto a smaller cog, making it
harder work to get up the hill!

Does anyone know how I can fix this?

Thanks in advance

Has your cable stretched? On a lot of derailleurs there is a small
adjusting barrel which you can unscrew a little to tighten the cable.
--
peter

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jim newman said:

[Apologies for non-technical terms used]

That's OK.

Quoted message said:

Does anyone know how I can fix this?

Two possibilities spring to mind, depending on other (not stated)
circumstances.

The most likely, in my opinion, is that the cable has stretched
slightly. This is normal, and is cured by adjusting a little "nut"
thing on the top of the deraileur (the arm that moves the chain across
and takes up the slack), where the cable reaches the deraileur. If
there is no adjuster "nut", then undo the clamp, pull the cable
through a bit more, and tighten it again.

The other possibility is that your shifter is loose in some way. Do
you have modern shifters that click into place, or old(er) fashioned
ones that you have to tweak until they are just right (usually mounted
on the frame)? If the latter, then you need to tighten the securing
screw a little to increase the friction.

Hope this helps. No doubt others will be along soon to expound on my
words some more.

PhilD

--
<><

jim newman said:

The chain on my bike keeps jumping down a gear
automatically. That is to say, it seems to want
to be on a smaller back-cog than I set it on.

Probably just needs a quick tweak on the adjustor where the cable goes
into the der. Try turning it one way and then the other to see how it
moves the little jockey wheels in and out, then tweak until the chain
lines up nicely with whatever cog its supposed to be on. For
mountains of detail take a look at Indexing adjustment here:

http://www.sheldonbrown.com/derailer-adjustment.html
or here
http://www.parktool.com/repair/readhowto.asp?id=64

jim newman said:

[Apologies for non-technical terms used]

The chain on my bike keeps jumping down a gear
automatically. That is to say, it seems to want
to be on a smaller back-cog than I set it on.

There doesn't seem to be any particular pattern
to this, it can happen at any time, and in any
gear, and seems to be happening quite frequently
and started this behaviour all of a sudden.

It is quite a problem when going up a hill and
the bike jumps onto a smaller cog, making it
harder work to get up the hill!

Does anyone know how I can fix this?

Thanks in advance

rought guess the derailer is way out of ajustment, and thus is jumping
up a gear.

<http://sheldonbrown.com/derailer-adjustment.html#rear>

has a fairly good how to.

roger

in message <[email hidden]>, jim newman

(') said:

[Apologies for non-technical terms used]

The chain on my bike keeps jumping down a gear
automatically. That is to say, it seems to want
to be on a smaller back-cog than I set it on.

There doesn't seem to be any particular pattern
to this, it can happen at any time, and in any
gear, and seems to be happening quite frequently
and started this behaviour all of a sudden.

It is quite a problem when going up a hill and
the bike jumps onto a smaller cog, making it
harder work to get up the hill!

Does anyone know how I can fix this?

Thanks in advance

Something is slipping. If you have an old fashioned downtube shifters, just
tighten the clutch bolt on the shifter. If not, you'll need to tell us a
lot more about your setup over all. What make of derailleurs, what sort of
shifters.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

The trouble with Simon is that he only opens his mouth to change feet.
;; of me, by a 'friend'

PhilD wrote on 30/05/2007 13:49 +0100:

Quoted message said:

jim newman said:

[Apologies for non-technical terms used]

That's OK.

Quoted message said:

Does anyone know how I can fix this?

Two possibilities spring to mind, depending on other (not stated)
circumstances.

Third possibility with a full suspension bike is the cable housing
between the main frame and swing arm is too short so that the gear cable
gets pulled as the suspension moves. That one took me a while to
diagnose a few years back.

--
Tony

"The most savage controversies are those about matters as to which there
is no good evidence either way."
- Bertrand Russell

Tony Raven said:

PhilD wrote on 30/05/2007 13:49 +0100:

Quoted message said:

jim newman said:

[Apologies for non-technical terms used]

That's OK.

Quoted message said:

Does anyone know how I can fix this?

Two possibilities spring to mind, depending on other (not stated)
circumstances.

Quoted message said:

Third possibility with a full suspension bike is the cable housing
between the main frame and swing arm is too short so that the gear cable
gets pulled as the suspension moves. That one took me a while to
diagnose a few years back.

Has anybody mentioned chain length/tension yet? I have had gears jump when
riding over a bump if the chain was a bit too long, the derailleur spring
or settings dodgy, or the chain in a small chainring/smallish cog
position.

Roos