I've got a 6 year old Diamondback Ascent 3.0 dualie, and I can't for the life of me figure out what this part is.
It's located right under the rear brake cable, and pivots up and down only a little ways because the brake blocks much of its movement.
http://img.photobucket.com/albums/v498/babybunny007/P1010002copy.jpg
http://img.photobucket.com/albums/v498/babybunny007/P1010003copy.jpg
http://img.photobucket.com/albums/v498/babybunny007/P1010004copy.jpg
http://img.photobucket.com/albums/v498/babybunny007/P1010001copy.jpg
It's located right under the rear brake cable, and pivots up and down only a little ways because the brake blocks much of its movement.
http://img.photobucket.com/albums/v498/babybunny007/P1010002copy.jpg
http://img.photobucket.com/albums/v498/babybunny007/P1010003copy.jpg
http://img.photobucket.com/albums/v498/babybunny007/P1010004copy.jpg
http://img.photobucket.com/albums/v498/babybunny007/P1010001copy.jpg