- Driveline imbalance: The driveline, which includes the transmission, driveshaft, and differential, can vibrate if there is an imbalance. This can be caused by a bent or damaged driveshaft, a loose or failing universal joint, or a damaged differential.
- Torque converter: The torque converter is a fluid coupling that transfers power from the engine to the transmission. If the torque converter is damaged or worn out, it can cause the car to shake.
- Engine mount: The engine mounts are the rubber isolators that hold the engine in place. If they are worn or broken, they can allow the engine to vibrate excessively, which can cause the car to shake.
- Damaged flywheel or flex plate: The flywheel is a heavy metal disk that is attached to the engine's crankshaft. It provides inertia and helps to smooth out the engine's power pulses. If it is damaged or warped, it can cause the car to shake. The flex plate is a thin metal plate that connects the engine to the automatic transmission. If it is damaged or warped, it can also cause the car to shake.
- Faulty transmission sensor or solenoid: A faulty transmission sensor or solenoid can cause the transmission to shift incorrectly. This can lead to the car shaking as it shifts into 4th gear.
If you've already replaced the CV joints, rotors, pads, and balanced the tires, and the car is still shaking when it shifts into 4th gear, it's best to take it to a qualified mechanic for further diagnosis and repair.
