Riddle me this:

My front derailleur won't move. I've tested it by pushing the mechanism with my finger and it appears to move the way it is supposed to move. But the cable won't move it. The cable is as tight as I can make it, but it still won't budge the derailleur when I move the shifter. Any ideas on what I can do to make it work?

To be up-front, while I'm comfortable many aspects of bicycle mechanicing, I've never once in twenty years felt like I understood how the front derailleur actually works and have always given up and taken it to my lbs after I've changed out the cable and messed with it myself for awhile.

I have a very old set-up. Non-indexed stem-mounted friction shifters. This bike was a 10-speed, but has been upgraded to a 12-speed. The shifter levers themselves seem to work fine.

The cable housing actually needs replacing (it's pretty shredded, but the cable itself is not broken).

I picked my bike up after some work not related to the front derailleur. My bike was in exactly the same condition as it is now, and it worked fine. Shifted through all the gears.

When I got it home, I don't know what I did, but I heard/felt something pop after I shifted into high gear, and now the cable won't move the derailleur even though the cable is not broken, and the derailleur appears to be working properly otherwise.

Any ideas on what could be going on?

I won't have a chance to go to the lbs during business hours for a few days, but I will be riding each day until then, so I would like to fix this myself if I can.

First rule of troubleshooting: fix what you know is wrong before going further. Treat yourself to new inner wires too, while you have everything apart.

OK, start at the beginning working backward from the known to work until you get to doesn't work.

So, you know you can push it meaning the FD itself is OK. Now find a place to grab the inner wire and pull it to see if the FD moves. If it doesn't then you know the problem is between your hand and the FD. If it works repeat the process working back to the lever.

In your case, based on the info provided, I suspect that the issue may bge related to the housing, which may be compressing under the load. But that's just a guess, and it's up to you to isolate the issue methodically

For a bike that old with cable housing in bad shape, it sounds like there's no question you need new housing. The housing is a critical part of the transmission. (For a system this simple, every part is critical.)

If one housing failed, the rest are probably close behind. Get new cables too. It can get hard to push old cable into a new housing, and they're not expensive.

Use the old housings as guides for cutting or buying new ones.

You may be surprised at how that project will improve your shifting.

The "pop" may have been the cable pulling loose in its bracket clamp. Put the der in its rest position and see if there is slack in the cable. If there is excessive cable slack while in the rest position (usually on the small chain ring) the cable has slipped. Loosen the clamp screw, grab the cable end with a pair of pliers, gentle pull it to remove the slack and tighten the clamp bolt while keeping the cable taught. It's easier than it sounds. Keep us in the loop and good luck to you.
For learning how to fix "old school" bikes, pick up a copy of "Any body's bike book" by Tom Cuthbertson. I still ride an '84 old school Peugeot (bought it new) and Tom's book has kept it going all these years.
Jon

I had the same problem with one of my bikes. Front derailleur worked fine one day. Totally frozen the next. I have a strong grip and it still wouldn't move. It turned out that the guide under the bottom bracket had gotten gunked up with something and the cable was completely locked in it. Cleaned and lubed it and it was back in business.

The most likely culprit is friction in the cable housing. If there is a dependent loop of housing, water can collect in that loop and eventually rust the cable, causing it to bind. Replace the cable and housing and you should be good.

Another possibility is a cable routing problem. Some front derailleurs, particularly top-pull models, have non-intuitive cable routing and won't work if you hook things up wrong. If you've just replaced the cable and it doesn't work, this could be the problem. Post a picture of your derailleur and how it is connected to the cable and perhaps someone here can help.

Thanks everyone. While the cable housing was defiantly having an effect, there was also an issue with how the cable was attached to the derailleur (JD Thompson nailed it). I was able to take it to my LBS and they actually had to mess with it for awhile until they figured out how it had been made to work before (I should have mentioned that this was not the original derailleur and I'd had to have my LBS MacGyver it a little bit to get it to work with my setup).

While this repair was going on, they sold me a 1972 Royce Union 5-speed that is perfect for me. My Univega is now up for sale. More on that in another thread. I just wanted to let you guys know how this particular situation resolved.

My new bike doesn't have a front derailleur, though, so I guess I'll never understand them fully.

I hope you didn't pay much for that Royce Onion. They were the lowest of the low back then and they only cost about $50 new.
Jon

Watch it shift while on a workstand. It's quite simple. It Just moves between 2 positions on a double crankset, pushing the chain from 1 chainring to the other.

Some can be a bit finicky to set up....getting the height right, and alignment, but plenty of on-line instructions to help.

Note to self: buy workstand.

Seriously though, I've been thinking about how useful one would be for years. What sort of prices can I expect?

So $14 wouldn't be bad for a used one.