The symptoms of a bad torque converter include torque shudder, a whirring sound at start up, and less power at lower speeds, according to ETE Reman. The most serious sign is a loud clacking or grinding, which indicates that the torque converter is beginning to disintegrate.
The first symptom that a torque converter is beginning to go bad is the engine revving higher than normal, indicating that the vanes are beginning to bend, reports ETE Reman. As the vanes bend further, the car may shift gears more slowly or not be able to drive at all. The car may experience torque shudder, which is when the engine block shakes as the car accelerates. As the torque converter continues to wear down, the transmission takes longer to engage the engine, and the car may stall. Once the car starts making a clacking or grinding sound, continued driving may cause tiny shards of metal to circulate throughout the transmission, requiring a total replacement.
Testing a car for torque converter issues includes starting the engine, letting it run for five minutes, revving it gently with the gas pedal, then shifting it into drive to listen for whirring, claims ETE Reman. Another way is to take the car for a test drive.