Rear mech changing problem

[4F]

I am running campag mirage 8 speed and this morning it just stopped shifting from large ring to small. I assumed a snapped / frayed cable however upon checking this is fine. I have been on the park tools / sheldon sites and tried adjusting however it will shift from small ring to large but not back down again.

What am I missing ?

 

[spandex]

When you try and shift down dose the cable go slack? if so it is your mech, if not it is your shifter. With out undoing the cable from the mech unclip it all from the bike and as if it all moves ok? To me it sounds like the spring is not pulling it back to test this you can take the chain off and push/pull the mech upto the big ring and then see if it gose's back if not try and lube and see if something is in there.

 

[4F]

Yep cable goes slack on shifting down. I have now managed to get it to change down from 1 to 6 by but it stubbornly refuses 7 and 8.

Cannot take the chain off as my work collegue has not retuned my splitter yet. The rear mech is gleaming clean and I cannot see anything in there so maybe a spring issue as the mech certainly does not feel as forceful as my sachs huret running on my other bike.

 

[Jonathan M]

FFFF, is it the rear gears or the front that you're having problems with?

If it is the rear then you might need to look at cables, sometimes dodgy shifting from large cog to small can be because of lots of stickiness & friction between the cable inner & outer, the friction makes less difference going the other way becuase the shifter is pulling the cable through and overcomes it. Look towards the rearmost loop of cable outer if you think this could be the problem.

The other things to consider with dodgy rear shifting is whether any of the limit screws have been incorrectly adjusted, or is the mech or its hanger bent at all due to an accident or just dropping the bike at some point?

 

[jimboalee]

If the FRONT changer shifts from small to large, but not large down to small, and the cable goes slack, the PIVOT BEARINGS in the front mech could have gotten full of road salt and shoot, partially seized overnight and now they need cleaning out.

Lots, I mean lots of cyclists buy a bike and don't apply any weather protection.

When its freed up, smother the pivots with furniture polish.

Where's the category 'Maintenance tips'?

 

[4F]

FFFF, is it the rear gears or the front that you're having problems with?

If it is the rear then you might need to look at cables, sometimes dodgy shifting from large cog to small can be because of lots of stickiness & friction between the cable inner & outer, the friction makes less difference going the other way becuase the shifter is pulling the cable through and overcomes it. Look towards the rearmost loop of cable outer if you think this could be the problem.

The other things to consider with dodgy rear shifting is whether any of the limit screws have been incorrectly adjusted, or is the mech or its hanger bent at all due to an accident or just dropping the bike at some point?

It's the rear mech, as it is ergo shifters surely the limit screws will not be an issue and no the bike has not been dropped or hit.

 

[4F]

If the FRONT changer shifts from small to large, but not large down to small, and the cable goes slack, the PIVOT BEARINGS in the front mech could have gotten full of road salt and shoot, partially seized overnight and now they need cleaning out.

Lots, I mean lots of cyclists buy a bike and don't apply any weather protection.

When its freed up, smother the pivots with furniture polish.

Where's the category 'Maintenance tips'?

Errr title of thread says "rear mech changing problems" It has not been ridden in the wet and the mech is spotless.

 

[jimboalee]

The confusion arose when you said "large ring to small".
Rings are on the crank spider and the front mech moves the chain from ring to ring.

The rear mech shift the chain up and down the sprockets.

Jonathan M could well be correct.

 

[4F]

Jonathan M could well be correct.

Do you mean with regard to cable friction ?

 

[fossyant]

Yup - likely cable drag - either replace cable, or remove and clean it and ensure the outers are clean/run freely. Disconnect from mech and feel if there is loads of friction !

 

[4F]

OK thanks all, job for tonight then. On the plus side Mrs FFFF now believes me when I told her it was essential that I had 2 bikes

 

[Sh4rkyBloke]

OK thanks all, job for tonight then. On the plus side Mrs FFFF now believes me when I told he it was essential that I had 2 bikes

You're married to a LadyBoy?? How's that going for you?

 

[4F]

You're married to a LadyBoy?? How's that going for you?

Thanks for your concern Sh4rky, now corrected

 

[4F]

When you try and shift down dose the cable go slack? if so it is your mech, if not it is your shifter. With out undoing the cable from the mech unclip it all from the bike and as if it all moves ok? To me it sounds like the spring is not pulling it back to test this you can take the chain off and push/pull the mech upto the big ring and then see if it gose's back if not try and lube and see if something is in there.

It's the mech , spring tension not so good and confirmed by my lbs
and new campag 8 speed rear mechs are a thing of the past.

So as far as I can see my options are:
2nd hand 8 speed mech and hope tension is better than what I have
9 speed mech (my lbs says this should work)
New 10 speed groupset (not really an option at the moment)

Any other suggestions / comments ? , for example is there anywhere that can replace springs on old mechs ?

 

[fossyant]

Since when did any mech's tension fail...??

Does the mech have any major 'bush play' - i.e grab hold of the bottom of the cage and wiggle - is there any big play....... My old DA 7400 suff has none, my Ultegra has a 1-2mm play, my old battered Deore LX has lots more, but it all still works....

Does the mech spring back if you 'twang it' - if yes OK......

Cables first, mech then duffed changers !!!!