Is this for a MIDI keyboard? I have found that MIDI continuos controller (CC) pedals work better at controlling volume than passive volume pedals, which usually work by shunting the audio signal to the ground via a potentiometer and are subject to "dirty pot" syndromes. MIDI CC pedals can control the volume (CC#7) or expression (CC#11) smoothly. See if your keyboard has an input for a CC pedal and try that.

Your current volume pedal may work better if you get some color tv tuner cleaner from Radio Shack and spray it into the pot.