Okay, I have a Trek 4500 SL and I have been having a lot of problems with my front AND rear derailleurs. My front derailleur has been having problems with down shifting from second to third. I tried futzing with my L Screw, and it shifts a little better now, but still sticks and makes some noise and then goes down. The derailleur isn't amazingly nice, so I don't expect it to shift perfectly smooth; but this is getting to be a pain in the ass when I'm riding and down shift but am still riding in second. Also when in third gear up front, when I peddle hard at all, it makes a kind of cracking/cranking noise, and I don't know where to start.
My rear derailleur is more of a problem though. The rear derailleur shifts fine both up and down, but when in any gear up front 1-3; the rear derailleur has problems in 1-4. Any hard peddling again will make the chain skip, like it has lost all tension. It doesn't always lose tension, but when peddling it will always skip a little, and it's noticeable if you watch the tensioner; it kind of pops every three seconds when peddling. I have just gotten this bike a little over two months ago, and I don't really know what to try and tweak on it, all I know is that the problem is progressively getting worse, because when I got the bike the read derailleur had none of these problems, although the weird noise on the front derailleur has always been present.
Is it possibly just the chain that needs to be replaced, or would I be well off to just replace the whole derailleur system.