[vettehead]

On a double piston caliber setup, such as a Corvette, when the wheel assembly is "out of round" (when a rotor has been taken off and put back on differently, for example) it causes air to be pulled back into the brake lines through the calipers because the calipers are uneven on the rotor. Not instantly noticed...but after a few spirited braking manuevers..you'll definitely see the results...no brakes!