Bicycle Mechanics - Front derailleur cage loose?

The other day I was checking over my bike, an old Trek 830, trying to figure out where a creaking noise was coming from. I'm a bit of a noob when it comes to mechanical issues, but I've been riding a lot more the last couple of years, using the bike now for commuting, shopping, etc., so I figure it's time to learn to do some maintenance myself. The first thing to I tried to do is see if anything is loose that's not supposed to be loose. One of the things that I notice is that the cage on the front derailleur is loose--I can just rattle it with my hand. I have been having occasional difficulty shifting the front gears--I have to shift a couple of times before the chain actually moves. So I'm thinking this is not right. But the information I've been able to dig up so far is not clear. Is this a) not a big deal, b) repairable/adjustable, or c) it means the derailleur is busted, and should just be replaced?

It means the derailleur is worn out.

It's hard to say what is wrong without some detailed photos. Front derailleurs have several likely possible causes of failure. I am not aware if the derailleurs (probably Shimano Altus or Alivio) are meant to be repairable.
Replacement with a new derailleur of the same quality will proably be within $25 - $50; something simple just to get you rollin' again might be a little as $10, maybe less if you have a source for used parts.

It's hard to say what is wrong without some detailed photos. Front derailleurs have several likely possible causes of failure. I am not aware if the derailleurs (probably Shimano Altus or Alivio) are meant to be repairable.
Replacement with a new derailleur of the same quality will proably be within $25 - $50; something simple just to get you rollin' again might be a little as $10, maybe less if you have a source for used parts.

Photos will tell you nothing. This is something you have to physically feel for yourself. When the FD is sufficiently worn out, the entire cage will have play - enough sometimes to cause shifting problems. At that point you replace it.


I am not aware if the derailleurs (probably Shimano Altus or Alivio) are meant to be repairable.

They are repairable. Spare parts, and their part no's are available in shimanos techdocs - directly available from shimano. It's usually not ecnomical to do this unless they derailleur is 105 level+.

It's a Shimano Acera-X derailleur, and it does appear I could get a replacement for pretty cheap--cheap enough that I might as well just go ahead and put a new one on. Thanks for the help.