When your car starts to shudder, it's a sign that something is wrong with the transmission. The most common cause of transmission shudder is a problem with the torque converter. When the torque converter isn't working properly, it can cause the engine to shake or vibrate. Other causes of transmission shudder include worn out motor mounts, faulty spark plugs, and bad wheel alignment. If your car is shuddering, take it to a mechanic so they can diagnose the problem and fix it before it gets worse.