Advice about front shifter

[UphillSlowly]

One of my bikes is a Giant Defy, with Shimano 105 group set. When I am not on the bike the front shifter seems to work perfectly, but when I am riding the chain seems "reluctant" to shift into the small ring. It is less of an issue if I happen to be freewheeling, but that's not always practical.

Sometimes it feels like the only way to solve the issue is to move into a larger cog on there rear cassette, then adjust. Furthermore, sometimes when I press the downshift gear lever for.the front derailleur it just wiggles inwards with no resistance and I have to press it again, closer to the hood.

Is this a case of needing a new gear cable? Frustratingly i can't replicate the issue when tinkering off the bike. I think the shifter positions are fine (no rubbing).

Thanks

 

[Paulus]

Could well be the time for new inner and outer cables. It sounds like they are sticky for whatever reason.
I presume that the mechs, and chain are clean.

 

[UphillSlowly]

Could well be the time for new inner and outer cables. It sounds like they are sticky for whatever reason.
I presume that the mechs, and chain are clean.

Thanks. That's what I thought. Roads have been mucky recently, so will give a thorough clean to see if makes a difference, but it's been an issue for a while

 

[13 rider]

Thanks. That's what I thought. Roads have been mucky recently, so will give a thorough clean to see if makes a difference, but it's been an issue for a while

I lost downward shifting on my front derailleur the other week . A good clean and a dose of wd40 on the derailleur cured it and it's been fine since , This would be my first move before looking at cables etc

 

[UphillSlowly]

I lost downward shifting on my front derailleur the other week . A good clean and a dose of wd40 on the derailleur cured it and it's been fine since , This would be my first move before looking at cables etc

The odd thing (which I.should.have made clear) is that the derailleur moves across fine, but it feels that if there is too much tension in the chain it doesn't want to move across. Only an issue while cycling, but not when it's on the stand. And then every now and again it feels like the shifter is not connected to the derailleur. Quite odd.

 

[Ajax Bay]

Has unscrewing the FD L limit screw no beneficial effect?
The shift obv won't happen when you are "freewheeling" (chain not moving).
Typically it's good practice to ease off while shifting down or up at the front.
On the stand chain tension is minimal so "it works perfectly". However when the chain is under tension it will need a bit more of a 'shove' from the cage (aka a millimetre further left).
When in small/large and what is the gap 'tween chain and inner cage plate?

 

[andrew_s]

The odd thing (which I.should.have made clear) is that the derailleur moves across fine, but it feels that if there is too much tension in the chain it doesn't want to move across. Only an issue while cycling, but not when it's on the stand. And then every now and again it feels like the shifter is not connected to the derailleur. Quite odd.

That happens.
If something long and thin is under tension, the higher the tension, the harder you've got to push sideways on the middle to deflect it by a certain amount. It doesn't matter whether it's a bike chain, a bit of string, or a spoke.
On the stand, you are turning the cranks with one hand, not pushing much, so the chain tension is low.
Going up a steep hill when you want to change in to the small ring, you are standing on the cranks and the chain tension is high.

In both cases the amount of sideways push from the front mech is the same (coming from the front mech spring), and the sideways deflection in the former case is more than in the latter. If the chain isn't pushed far enough over, it doesn't change.

To help matters...
a) ensure that the front mech spring tension isn't wasted by trying to drag the inner through a mucky housing.
b) try to time your gear change so it happens when the chain tension is relatively low - i.e. the cranks are vertical. It can also help to give a bit of a pre-change stomp to allow you to ease off the pedal pressure during the change.

 

[boydj]

I'd try slackening the cable on the front shifter just a touch and/or take a fraction of a turn off the lower limit screw. When you're
on the small chaninring there should be a touch of slack in the cable.

 

[Alex321]

And then every now and again it feels like the shifter is not connected to the derailleur. Quite odd.

I have that issue with my rear shifter (also 105). When trying to shift into a higher gear (smaller sprocket), it sometimes just clicks freely, without appearing to be connected to anything.