In our family’s fleet of bicycles is a Trek 360 (1980”s). I am having much trouble adjusting the front derailleur. It will only shift up from the smaller chaining to the larger, but not down. I have tried adjusting the angle of the derailleur by the derailleur bracket attached to the front fork as well adjusting the tightness of the cable. This particular derailleur has only a single adjustment screw which seems to control only the outward movement. Could it need a new cable? I have spent hours trying to correct the problem and am about to pull out my remaining hair. Please HELP!