Front derailleur randomly not changing

[Fifelad]

Strange one this. The derailleur changes perfectly the majority of the time, then every so often fails to change. I did think it could be due to the fact that I don’t have it clamped in the way on the shimano derailleur where the arrow guides the cable, for those that are familiar, as believe it or not it is a much smoother change not clamping it in the recommended way. It’s on a Cube Agree, not that should be relevant. Thoughts ?

 

[richardfm]

Strange one this. The derailleur changes perfectly the majority of the time, then every so often fails to change. I did think it could be due to the fact that I don’t have it clamped in the way on the shimano derailleur where the arrow guides the cable, for those that are familiar, as believe it or not it is a much smoother change not clamping it in the recommended way. It’s on a Cube Agree, not that should be relevant. Thoughts ?

A photo showing how it is clamped and the cable routing and anchoring might help

 

[Big John]

If it was me the first thing I'd try is removing the cable from the front mech, holding the cable in one hand and pulling the lever with the other to see if the cable is moving freely. If it's a sticky cable that might account for it working one minute and not the next. If that was the case drop a new cable in but give a squirt of GT85 down the cable outer first by using the little red straw. If that doesn't work then you can try one of the next options......I'm sure there will be more than a few turn up 👍

 

[Ajax Bay]

Make and model of FD would aid diagnosis.
Assume dropping to small ring.

 

[Supersuperleeds]

Cable about to go?

 

[MontyVeda]

Mine's similar... but i don't clean it very often and it's probably the cold affecting the gunk

 

[Fifelad]

Thanks for the replies folks. Sticky cable sounds the most plausible reason. The cable is not that old and I always squirt some GT85 in the outer cables to aid movement. The bike is generally ridden in the dry in summer. Apologies for lack of photo evidence. I think I’ll put a new cable in and see how it goes.

 

[Cycleops]

Outer cables can often start rusting internally after just a few months if a cheap brand. Replace both and make sure to add grease to the cable. Clean the derailleur and oil pivot points. Should fix the issue.

 

[Ajax Bay]

Make sure not to add grease to the cable as it will increase friction between cable and outer.
Anyway @Fifelad is not going to have "cheap brand" cables on a Cube Agree, is he?

 

[Cycleops]

Dunno, but my Cube certainly has, 'cos I put them on.

 

[Spiderweb]

Make sure not to add grease to the cable as it will increase friction between cable and outer.
Anyway @Fifelad is not going to have "cheap brand" cables on a Cube Agree, is he?

He might if he’s Scottish😳

 

[froze]

I only mention this because it's outside of what everyone else is saying, I'm betting it's the cable, but if you still have a problem after replacing the cables then consider this stuff.

You could also be experiencing a weak spring in the derailleur; or a problem with the shifter itself.

Did you check to make sure you don't have a broken or bent or worn ring gear tooth or teeth? Random could mean that as you pedal and you shift the ring gear has to be just in the right position where that tooth is to prevent a shift. Most cases this would act more like a skip, but not always. Or the shift ramps on the gear ring are worn which would not make the chain skip, just fail to pick up correctly.

Spin the pedals and look down at the chainrings, check to see if there is a wobble in the gears, they should run perfectly flat but if the chainring got bent a bit or the chainring bolts are loose, it could be a wobble causing sporadic shifting.