After you pop the drives cover off hitting it with a hammer to bend the drive platters and kill the head assemble is the best way.
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After you pop the drives cover off hitting it with a hammer to bend the drive platters and kill the head assemble is the best way. Follow this guide to get to it [https://www.ifixit.com/Guide/iMac+Intel+27-Inch+EMC+2429+Hard+Drive+Replacement/7555]