Hi-I will be replacing my derailleur cables for the first time ever (wish me luck) and I need your help.

From what I understand I can buy as complete shift kit or buy some of the parts separately (cables & housing) and use some of the parts already on the bike.

Is using the parts already on the bike (end caps, connectors etc) and replacing the cable w/ new one a recommended practice?

My bike (Spec Roubaix SL4) has internal cable routing. Do I need to use any housing inside the frame or is the liner that come with the kit used for that purpose? My understanding is you use liner to push the old cable thru the frame back out and do the reverse when installing the new one. Is that correct or does the liner stay inside the frame?

As you can tell I honestly have no idea how cables travel thru the frame. This will be a good learning experience.

I ride about 6000miles/year in mostly dry conditions in the Northeast US. I race maybe a dozen times. Could you guys recommend a decent brand? Shop installed Jagwire the last time but I am open to new ideas. Thank you in advance!!!!!

I'm by no means an expert mechanic, but I do usually replace my own cables. My feeling is to replace the cable housings periodically--although what 'period', I cannot say. On my racing bike, the shifting has been smooth, so I have left those alone but, on the rear brake, it was getting sticky and I couldn't fix it, took it to my LBS (local bike store). The mechanic determined that the housings were getting mucked up inside and replaced them, problem solved. This was on a racing bike with about 20,000 miles on it in almost exclusively dry conditions so, if you ride in the wet, the housings will no doubt get gucky much faster.
Regarding the internal routing, I have no experience with that. All I can suggest is that you (a) try doing a web search on it and (b) try to develop a relationship with an ace mechanic at an LBS (minimum 5 years full-time experience) and ask them. What I do is go in, buy something and then ask, so I'm not trying to 'mooch'...
P.S. I can't say for sure the derailleur cables are the originals from 20,000 miles ago. I may have replaced them at some point.

If you're replacing the housing, leave the cable in place as a guide and slide the old housing off and then slide the new housing over the old cable. Once the housing is in place, pull the old cable and install the new one. It's really pretty easy as long as you don't loose the free end of the housing inside the frame.
Jon

I made a video about a year ago with some tips on internal routed cables. There's an example in the video of a certain cable stop Specialized uses that needs a ferrule with a teflon guide tail or a short teflon tube in the cable stop itself.It may just be on the aluminum Specialized models, but if you don't use them, the cables will cut through the cable stop over time. The Jagwire cable kits are decent.

Jagwire is pretty good. Cables travel through free air inside the frame. Before pulling the old internal cables out, I would use the teflon tubes so that the new cable has a guide, which are not needed for final assembly. Just make sure you have the front housings cut to a good length before you pull the teflon tube back out

Holy cow man this is awesome thank you!

Thanks for the advice! I will keep these in mind.

Thanks for the advice Jon!