Originally Posted by
vasracer
If the bike is 10-15 yrs old how you stated, then i would replace both gear cables with housing and probably think about switching out the brake cables with the housing also. Many people will tell you not to change them if they feel fine but you don't know how long they have been there or if they have ever been changed before, and the last thing you want is for a brake cable or a gear cable to snap on a ride and become a hazard.
+1
It's cheap and your shifting/braking will be much crisper, not to mention the piece of mind you'll have knowing you'll be able to stop at the intersection at the bottom of the hill. You should replace the housing because it fills with grime and adds friction to the cable resulting in a sluggish feeling.