Took me 4 builds to stop reusing old shift cables, and a guy named Ray at the co-op in Boise showed me why
I used to pull cables off busted bikes and stash them in a coffee can, thinking a little lube would fix any rough spot. Then I did a full tune on a commuter and the rear derailleur still ghost shifted, so Ray at the Boise co-op cut the housing open in front of me and showed me the liner was packed with grit and rust. New cable and housing, 40 minutes of work, and it shifted like the day it left the factory. So my question is, how many of you actually keep a stash of used cables, or am I the only one who was hoarding junk?