No, they aren't desprately needed. The shims are to help prevent noise. You could re-use the ones you currently have on your car, but I don't know if the Axxis pads are thicker or not. You may not be able to get the caliper back on with the shims, but if you can by all means do it. Just remember to spin the rotor before you put it on the ground, just to make sure that it spins freely.