yes!! listen to hill rider and dabac because they are right. tighten the screws down that hold your shifter together. i have had this problem a long time ago, and everytime it is not enuff friction in the friction shifter, so do just as they say. never heard of it being a cable issue, but if that doesn't work, get a new downtube shifter that can be tightened down all the way/proporly. if cost is an issue, take the screw out, carefull not to let the shifter fall apart off the bike and add the propor, thin washer in between the outer screw and shifter. this'll keep the screw from bottoming out and preventing propor tightening if the shifters internal friction washers are worn.