I think I might see what is going on. The push rod and air supply line attach inside to a spindle valve, is this the part that you see just starting to exit the housing at the end of the throw? The tube I am refering to will only exit when the system has air pressure on the supply line and the valve is pulled out. If this tube is not coming out try this, remove the arm from the servo and push the push rod all the way in, and with pressure in the system slowly pull the push rod out and see if things work differently. If this works you are not starting with the valve far enough in.

let me know what happens

Steven