The DC-9's pedal travel results in a direct, proportionate rudder response, whether powered by a bit of right system hydraulic pressure or (no hydr.)mechanically with the (unlocked) control tab, from what I've always studied.
And the tails have no graphite epoxy or other synthetic, plastic sort of parts.
DC-9s, still flying since 1965, or '72! And no cold-bonding process, as used in the B-737-200 upper fuselage...remember the tragic Aloha Airlines emergency descent, minus one flight attendant?
Why was the A-300 weight reduction in the vertical fin worth the risk of undetected fatigue deep inside the tail? Were not the forecast operating temperature extremes a new element?