i drive a 91 caprice.....i wanted 2 change the back brakes from drums to rotors....i wanted 2 know what all i need 2 do this change?? i called a man at auto zone .and he said i needed a new axel i wanted 2 know if he was right before i did thiz....and how much it would cost me ????

I don't think a new axle is necesary, but a new axle tube hub on either side would be required to hold the brake caliper and new axle shafts would be needed to hold the rotor. It would be easier and potentially cheaper to simply get an axle from another car that has the disk brakes.