Originally Posted by
Kimmo
I think on 105 and below, they're riveted on. You could probably grind off the rivet and fit one from an Ultegra or Dura-Ace brake of suitable vintage, but in almost all cases you'd be better off just chucking another brake on (unless of course you found a busted brake of the right sort).
The new 105 BR-7000 has a removable brake cable QR but as you've mentioned, the BR-5800 does not.