Derailer cable tension issue

[steve30]

Long time since I last posted on here . Anyway, I was wondering if someone could advise me on my derailer cable.

Basically, my front derailer seems to require a lot more force to move it than I think it should. I can't remember if its always been like this or not. It takes quite a bit of effort on the lever (a Shinamo Tiagra) to move it all the way up to the big chain ring. Additionally, the cable has been rubbing on the bottom of the frame, and worn some of the metal away. Adjustments are also quite difficult due to how tightly the cable has to be pulled.

I tried to demonstrate this in a video but demonstrating cable tension is quite difficult in a video. The derailer itself moves nice and smoothly. Right before I shot the video I had it off for a thorough cleaning.

Video:

View: https://www.youtube.com/watch?v=xg4tT_LUqYc


Any ideas?

Thanks
steve30

 

[gbb]

I don't know about a Tiagra FD but a once every winter problem for my old Sora shod bike was siezing up at the derailleur pivot...thus creating a need for far more force to make it shift up, but i note you've said the derailleur shifts nice and smoothly.
So I'd be trying to isolate the problem and for me its be chain off, cable off, then ensure the FD travels fully and freely across the required range...which apparently it does.
Check the cables. Remove from outer making sure if travels freely and it's in good clean order, making sure they run smoothly in the outers. Check for fraying, check inside the shifter for fraying at the nipple.
Then I'd put the shifter into bottom gear, grab the cable right and shift upwards, seeing if it pulls the cable ...its not very scientific but it might highlight a problem with the shifter.

Theres probably a classic reason for stiff shifting, I don't know what that is so it's a process of elimination. Hopefully someone may come in with that classic reason and save you the faff.

 

[Smokin Joe]

If it has had the same cables since you bought it they would be my first port of call. New inners and outers will make a hell if a difference, and a bit of outer cable to protect the weld where the inner is rubbing it would be a sensible idea.

 

[Levo-Lon]

Just replace the inner,be like new again

 

[Outlaw Hobbs]

I doubt if it is the whole problem but maybe the FD cable has worn through the plastic guide on the BB? New guides are easy to find on a well known auction site and cost peanuts.

 

[raleighnut]

I'd go for an inner cable and new guide too, also checking the front mech travels smoothly and easily over it's range.

 

[Cycleops]

Just replace the inner,be like new again

... and add some grease.

 

[Smokin Joe]

Just replacing the inners would be only half the job. Eight year old outer cables will be chewed to bits internally and on 2010 Tiagra they will be external cables, doddle to fit with no bar tape to unwrap.

 

[mickle]

If the inner cable has been sawing its way through the frame perhaps thats the source of your resistance.

 

[steve30]

Thanks for the replies everyone.

The cables are actually only two years old. I put new Tiagra shifters on a couple of years ago to replace the original Sora ones, and replaced the cables while I was at it.

The inner cable is actually frayed at the derailer end. When I put it on, several of the strands broke. I'm sure this doesn't help, but I don't know how much it actually contributes to the problem, and it doesn't explain why the cable is sawing through the frame. Nonetheless it definitely needs replacing as a matter of urgency.

 

[Ajax Bay]

New inners and outers will make a hell [of] a difference, and a bit of outer cable to protect the weld where the inner is rubbing it would be a sensible idea.

This. You cannot know how much additional friction is being caused with cable (under tension) against the frame. An inch of outer (glued to frame) would address both that and stop any further damage to the weld.

the plastic guide on the BB? New guides

Examine the current guide and if it has shown significant wear, replace. But wear (ie to failure) of this under BB cable guide is not 'normal' - I would expect several 10s of thousands of miles. Worth a swipe of grease every month.

 

[steve30]

Is the cable mounting part of my derailer knackered?

This is the best I can get the cable to attach. I had a lot of difficulty attaching my previous cable a couple of years ago which is why it ended up knackered.

I did manage to hot-melt glue a small piece of outer cable on the bottom of the frame. It'll be interesting to see how long that will last.

 

[Ajax Bay]

Is the cable mounting part of my derailer knackered?

Provided the thread is OK inside and the bolt is similarly OK (easy to replace latter) then you should be able to clamp your cable securely. I would run the cable so it is inside the flange all the way, not cutting over the top of it. Screw in the lower limit screw before attaching. This will mean a bend in the cable as it starts to 'go under' the bolt head but may marginally improve the angle of pull of the cable (and might require less tension during a change up).

 

[Globalti]

The cable is attached correctly and you've managed to avoid over-tightening and crushing it, a common mistake. Cut it short and crimp on an end cap.

If you didn't replace the outers though, you may have wasted your time because a new inner won't perform any better if the outers are worn and rusted up or crudded up with oil and dirt.

 

[steve30]

It was still very hard to shift gears with the cable in the position shown in the above photos. Running the cable on the inside of the little 'nub' was virtually impossible as it just pulls out.

I put the cable above the 'nub' (see photo below) and now it works delightfully . No more stupidly high tightness, and I no longer have to put up with a frayed cable.