Bankruptcy and car loan?

In November, I made the decision to file bankruptcy and it was filed a week ago today. My problem is I recently purchased a car (4/4/11) and I have a car loan, but I want to surrender the car under the bankruptcy. The problem is the car is not in good shape as they told us it was (they said they replaced the transmission, but the transmission is stalling and jerking), and they are not willing to