Shimano Deore front derailleur return spring broken?

Question

For a couple of days now, I am no longer possible to shift to the smallest chainring of my bicycle. There is simply no response at all (no resistance, no click-sound, nothing happens. The indicator at the gear shifters placed on the handle only moves half the distance between the two gears...)

I have no idea about bicycles but I did some testing and research. My guess is, that the return spring at the front derailleur is broken. The cable is pretty loose (I can easily move it several centimeters by hand) and I can also turn the derailleur by hand. Especially the latter part lets me believe that the spring is broken since (at least to my understanding) the derailleur should be in tension and not easy to move by hand...

I might be using some terminology wrong here, thus, I have attached a picture: The cable highlighted in blue is very loose. I can rotate the thing in red by hand (which I assume should be under tension).

My questions are the following:

1. Does my diagnosis make sense or is it more likely that something else is causing the failure?
2. Is it easy to replace the spring with basic equipment or is it likely that I mess up and cause some damage?

I found some questions talking about having grease or mud in the derailleur that can be removed with WD-40 but I think in my case, something is more likely broken since there is no response at all.

Answer 1

The return spring on a normal front derailleur (FD) should pull the chain towards the smallest (innermost, towards the centerline of the bicycle frame) chainring. I cannot quite tell from your question whether there is no spring force being applied or if it has other issues.

If the spring is broken, that would not prevent the FD from being moved to the smallest chainring by hand (assuming there is slack in the cable). The things that could prevent the FD from moving to the innermost chairing (with slack in the cable) are:

• The L limit screw is turned in too far. The L (and H) screws are what limit the full travel of the FD. The L screw is what limits the leftward travel of the FD so the chain does not drop off the smallest chainring. When adjusted correctly, they prevent the chain from dropping inside of the small chairing and outside the largest chainring. Usually these are set correctly once and forget. If the L screw is screwed too far in, it will prevent the FD from moving all the way to the smallest chainring.
• There is some debris/a small rock or pebble in the FD mechanism. Every FD is a little different and it is possible that a rock or pebble has found its way into the mechanism, which can sometimes be difficult to see until it is cleaned out and moved to clear out the debris.
• The mechanism could have gotten dirty enough to build up friction that is preventing the full range of motion even under spring tension. This is pretty rare on a FD, as the spring is usually pretty robust. I have seen this on a rear derailleur before (the cage spring, not the travel of shift spring), and in that case cleaning and re-greasing restored proper operation.

If you can easily move the FD full-range by hand (with a slack cable), and the FD will stay in that position, then yes your FD spring is broken - replace the FD.

If you cannot move the FD full range (to the innermost chainring) by hand, then either the L screw or debris, extreme friction, etc. is preventing that movement.

As for your second question, FDs are relatively inexpensive and it would be worth just replacing it if necessary. The only situation where replacing the spring may warrant being explored is if you had a spare spring or more likely a spare FD (that may be junk because something else in it is broken/bent) that you could use the spring from it for the repair. That said, many FDs may still present a problem with them even being disassembled to replace the spring due to the way they are constructed. That part of the mechanism is not designed to be disassembled, so in order to take it apart you would most likely destroy it. Again, FDs are relatively inexpensive, so consider replacing it if indeed the spring has broken.