When to change shift cables
I have been noticing my shifting is not as good as it was used to be. I am not sure if I am just used to my SLX shifters and derailers or my cables are due. So far the cables and housings are just over a year old and have about 600 miles of use. The cables have been adjusted a couple times so far.
When in doubt change it out. Depending on whats happening when you shift it may very well be the cables. I typically get a good bit more than 600 miles on a set of cables. current set is at 2000mi (gore sealed system). If it feels kind of sticky probably time to change. Another common cause of poor shifting is a bent der hanger. Typically with this you can get it to shift well in the top or bottom of the cassette, but not both.
Take them apart, clean the cable and sleeve, and lube the cable with a light coating of white lithium grease, then put the cables back in the sleeves ... You'd only need to replace them if they are damaged/corroded.
My old bike is still running it's original cables, and is 25 years old w/SIS ... No problems, yet.
You only need to lube the cable if you run an old-fashioned system without plastic lining in the housing and galvanized cable. Modern cables are smooth and with the plastic lining inside the housing, any oil or grease will only collect dirt and increase friction.
I'd first check that everything is set properly and the cables and housings are clean. You can revive a used (not worn out) cable and housing set with simple maintenance. I'd hate to discard a cable set that still has a lot of spark left in it.
If you aren't replacing the housing, a new cable will run you about five bucks per shot for DYI. You should instantly realize a difference and wonder why you waited so long to change them. If you are taking the time to pull the cables, don't bother lubing and reinserting them. It is more trouble and will put put you right back into the binding problems much sooner than you want. If the cable replacement does not cure your problem, move on to the housing and repeat the process.
I live in dry SoCal and wind up swapping my rear cable 2 or 3 times a year. Every time I am amazed the difference of the before and after.
Apathy will get you exactly what you deserve
Shifter cables can be checked by disconnecting them at the derailleur ends, both FD & RD. You can get a good feel for how easily the cables move inside their housing by hand. It should be free and require very little effort to move in either direction. You can move either the cable or the housing.
My experience in dry dirt trails is that lubing cables only causes problems. Lube attracts and accumulates dirt onto the cables, and once inside the housings it will create friction and wear.
Using stainless steel cables with coated housings and NO lube will last for years without problems.
I ride dry dusty trails. I agree lubeing cables will only cause me more trouble than it is worth for my needs. I will most likely have my LBS do the swap for me. I like to keep my stuff in like new operation. I am kind of particular like that. I assume the housings last longer? If the cable is good could you just take the cable out of the housing, clean it and use a new housing? I would figure sticky cables would mostly be a housing issue?
BTW my cables are the stock Jagwire L3 that came on my bike