Abstract: An automatic derailleur shifter is disclosed which includes a hollow cylinder body and a piston rod movable within the cylinder. The piston rod carries a dual element piston within the cylinder body in a manner to permit substantially unrestricted fluid flow through the piston when the piston rod is moved in a first, upward direction and a greatly restricted fluid flow when the piston rod is moved in the second downward direction. A first, fixed piston element is fabricated of diameter less than the inner diameter of the cylinder to allow unrestricted fluid flow thereabout. A second, movable piston element is provided and below the fixed piston element includes a flared skirt for sliding, sealing engagement between the movable piston element and the cylinder. A small, restricted longitudinal channel is provided through the fixed piston element which terminates at its lower end at a circular channel.