You do not have to use the pads. You still have the dampening of the rubber bushings in the front perches and the rear shackles. Did you tighten the suspension down with the car up in the air or with the full weight on it making it loaded. If you tightened it up with no load on it you could have some binding going on in the bushings. Most of the shims that you can get are for adjusting the pinion angle. It's possible that one leaf might have more arc in it than the other one. It's also possible that something in the front is causing it. I would start with checking the air in all of the tires, body mounts, front coils, control arm bushings. Air up all of the tires and measure from the center of the rim to the fender lip. Is the front off at all? Sorry for rambling but I was typing as I was thinking. LOL