What causes a sudden 'bang' sound when starting an automatic transmission car?
2 Answers
Possible reasons for a sudden 'bang' sound when starting an automatic transmission car are as follows: There may be an issue with the transmission: loose drive shaft, transmission wear, worn output shaft inside the transmission, worn transmission gears, or a fault in the gear shift position, etc. It could also be due to parking on a slope with the P gear engaged before pulling the handbrake: when starting the car and accelerating the next time, it may cause a 'clunk' sound. Engaging the P gear first causes a pawl inside the transmission to lock the output shaft to prevent the vehicle from moving. In this situation, the car may slide slightly on the slope, putting all the vehicle's weight on the P gear. Therefore, when parking, it is essential to pull the handbrake first and then engage the P gear, so the force is on the handbrake.
I've experienced a 'bang' sound during startup, which is quite common and usually related to transmission issues, such as gear shift jerking or clutch plate slippage. Sometimes it could be caused by loose suspension components or faulty shock absorbers leading to abnormal vibrations. The braking system might also be involved, like rusted brake discs sticking together or releasing suddenly during startup, creating noise. On the engine side, abnormal spark plug ignition can cause slight engine knocking. Additionally, if there are foreign objects hitting the chassis on the road, they can also produce sounds. A startup noise like this indicates potential safety hazards, so it's recommended to stop and inspect immediately or visit a professional repair shop for diagnosis. Regular maintenance of transmission fluid and suspension components can prevent such issues, especially for automatic transmission vehicles which are easier to maintain. Ignoring it may lead to gradual worsening and more serious failures, affecting driving safety, so don't delay addressing the problem.
