Why does the car shake when shifting into P gear for parking?

[VanRhett]

When the vehicle is parked on a slope and shifted into P gear, it may shake back and forth slightly. In fact, this does not cause damage to the transmission. This occurs because there is a gap between the parking pawl and the parking gear. Due to the mechanical imprecision of the parking pawl, the vehicle may shake slightly back and forth after shifting into P gear and releasing the foot brake. Once the parking pawl engages fully, the vehicle will no longer move. Here is the relevant explanation: The P gear in automatic transmission vehicles is the parking gear, which is essentially an evolution of the N gear. In addition to placing the transmission in neutral mode, the P gear also includes a parking pawl inside the transmission and a parking gear on the power output shaft. When shifted into P gear, the parking pawl and parking gear inside the transmission interlock, thereby fixing the vehicle in place.