I bought my son a used MTB last year with these same shifters and the front wasn't functional when we got it. I took the shifter apart (pull the screw, loosen the shifter wire and it can be taken apart pretty easily) and used WD-40 and needle-nose pliers to get all of the cams and levers moving smoothly (I had to work a couple of parts numerous times before they were really moving freely enough to shift properly). Worked great every since.