No. A co-signer’s social security number will not be involved, and the bankruptcy does not go on their credit.
No. In short, if you file bankruptcy, your social security number is the one the bankruptcy attaches to. A co-signer’s social security number will not be involved, and thus the bankruptcy does not go on their credit.
But, unless you or your co-signer are making regular on-time payments on the debt even after your bankruptcy case has been filed, your co-signer's credit score will be negatively impacted. If you stop making payments on the debt, and your co-signer isn't making payments either, this will be reported to the credit bureaus for both of you. This happens irrespective of whether a bankruptcy has been filed. Your Chapter 7 discharge will not protect the co-signer from creditor actions.
If you have a co-signer on your car loan, check out this article to learn more about how this will work.