Rear Derailleur Problems - Go Down one at a time - go up two at a time

PUSHERBOT was thinking very hard :
I've got the following problem with an indexed Shimano Acero rear
derailleur on my MTB.

Shifting from smallest cog to biggest cog works fine - one cog at a
time. I'm pretty sure the tension is right or at least pretty close
here. However, when shifting from biggest cog to smallest cog, the
derailleur will only shift two cogs at a time on every 2nd click of
the changer(or at least it is when going from 8-6 and 6-4).

I've taken the cable off, given it a clean and retensioned, but it
still seems the same. I'm guessing that replacing the cable and maybe
the outer will solve the problem, but before I do that, could it be
anything else?

Paul's suggestion is reasonable, although spring problems
are(especially at a time of year when there's not much risk of
corrosion) not the most common cause of problems, and your response
suggests it isn't the issue this time.

If you assemble the cable but don't route it into the mech you'll be
able to pull it backwards and forwards a few times - it's likely you'll
be able to tell if there's any problem there. If it's clean and
lubricated you could also check that the outer hasn't been crushed, or
its ends damaged. Could their be a problem with the cable length? This
can be caused by raising the bars, for instance.

Next I'd check that the mech or the hanger haven't been bent, possibly
through the bike being dropped. It's perfectly possible for the mech to
continue to work in one direction and not the other. It can be hard to
check, though, and ideally you need to get the hanger checked at a shop
with a special tool. Nonetheless, this may have rung a bell, perhaps?!

Good luck.

--
Simon
www.simondaw.freeserve.co.uk

Simon D said the following on 16/09/2006 14:59:

Paul's suggestion is reasonable, although spring problems are(especially
at a time of year when there's not much risk of corrosion) not the most
common cause of problems, and your response suggests it isn't the issue
this time.

I didn't mean to imply that the spring itself was the problem, although
I can see how it looked! I really meant that the spring wasn't *able
to* do it's job because of other factors such as stickiness somewhere.

--
Paul Boyd
http://www.paul-boyd.co.uk/

in message , Paul Boyd
') wrote:

Simon D said the following on 16/09/2006 14:59:

Paul's suggestion is reasonable, although spring problems are(especially
at a time of year when there's not much risk of corrosion) not the most
common cause of problems, and your response suggests it isn't the issue
this time.

I didn't mean to imply that the spring itself was the problem,

Certainly not. It's the autumn and winter that are the problems...

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

Morning had broken, and we had run out of gas for the welding torch.

On 18/09/2006 17:18, Simon Brooke said,

Certainly not. It's the autumn and winter that are the problems...

Ho ho ho!!

--
Paul Boyd
http://www.paul-boyd.co.uk/