Possible causes of impact when engaging a gear in an automatic transmission:
1. Torque converter malfunction:
* Worn torque converter lockup or other components.
*Low transmission fluid level.
* Contaminated or improper transmission fluid.
2. Problems with gears:
* Worn or damaged gears, bearings or synchronizers.
* Low transmission fluid pressure, which leads to clutch slipping.
* Faulty gear shift solenoids.
3. Problems with the transmission control module (TCM):
* Fault in TCM wiring or components.
* Bugs in TCM software.
4. Wear of engine or transmission components:
* Worn flywheel or flex plate ring gear.
* Faulty engine or transmission support bearing.
* Worn drive shaft splines.
5. Other possible reasons:
* Faulty exhaust system causing shock due to back pressure.
* Damaged or worn motor mounts.
* Malfunction in the engine or transmission vibration reduction system.
What to do if the automatic transmission knocks when you engage the gear:
* Contact a car service to diagnose and repair the problem.
* Check the level and condition of the transmission fluid regularly.
*Follow the recommended transmission replacement and maintenance schedule.
* Avoid sudden acceleration and towing heavy loads.
* If you experience problems with shifting gears, do not operate the vehicle to avoid further damage.