if the nylon rods are not suported or installed in a 's' type pattern they will flex.use 1/4 dowel with a piece of 1/16" wire at the servo end with a z bend then a threaded rod at the other end you may have to make a few bends to exit the fuselage if you do only make 45 degree bends do not make 90 degree bends as they will flex too.I would check the nose gear linkage first to see if it is binding then check the servo for stripped gears as there really is no load on the rudder while in flight.