Tiagra left shifter sticking

[wyre forest blues]

I have an oldish (2014?) Cannondale Synapses bike with Tiagra shifters. I think they are the 4600 with the window displaying the gear position. I havent used it for some time but now need to lend it to my son in law. The front left shifter is a double. When I shift down to the small ring the normal smooth operation is now heavily resisted followed by what can best be described as a clunk and sharp sudden movement as the mech moves the chain to the small ring. Moving back to the large ring works perfectly. I'm pretty sure its not the mech which is faulty. Has anyone encountered this issue and if so can it be fixed or is a new left shifter needed.

 

[figbat]

Cable frayed? Or rusted?

 

[boydj]

Look at the cable inside the shifter - that's where they tend to fray. It does sound like a cable problem and you can confirm by detaching the cable at the mech then moving the mech by hand and checking the cable movement when operating the shifter.

 

[Globalti]

The clue is always the same: "I haven't used it for some time....." meaning the cable has rusted or was fraying last time you used it but the deterioration was gradual so you didn't notice it.

 

[ianrauk]

It's always seems that the left hand brifter goes first. If it's not the cable of course.

 

[wyre forest blues]

Thanks for all your suggestions. A project for me tomorrow.

 

[Ajax Bay]

Greater tension on the FD (cf RD) cable

 

[Gunk]

I agree that it probably an inner cable, as they’re cheap I’d pop a new one in anyway, however check that the front mech moves freely as they get all gummed up with old congealed grease, it’s an easy job to get it off the bike and service it on a bench, you can then get to everything and make sure every joint is spotless, don’t over lubricate it, a spot of waterproof lube on all the pivot points is all it needs.

 

[Smokin Joe]

A 2014 Tiagra shifter will have exposed cables, so it is not worth replacing just the inner. I'd definitely renew the outer too.

 

[Gunk]

Good point!

 

[Globalti]

A Park Tools cable cutter is probably my most useful workshop tool.

 

[Ajax Bay]

I would additionally recommend a good dousing of sprayed oil (GT85/WD40) through every orifice of the STI.

 

[Globalti]

9 times out of 10 it's the cable, not the shifter or the derailleur.

 

[Ajax Bay]

the cable has rusted or was fraying

"9 times out of 10" - agreed, hence my use of "additionally" (especially for a 'unused for a long time' STI).
Why would a stainless steel gear cable 'rust'? Mine don't.
I'd also point up that the ST-4600 (and earlier) STIs suffer fraying in the mechanism much less frequently as they are not bar-routed but washing line style.

 

[Globalti]

Cheap non-stainless cables do rust though. I've also seen bad designs of brake arms where the cable gets bent very locally every time the brake is applied so it work-hardens and eventually snaps.