The main reasons for jerking when changing gears in an automatic transmission:
1. Problems with electronics:
* Faulty automatic transmission control module (TCM)
* Damaged wiring
* Faulty sensors (input shaft speed sensor, output shaft speed sensor, selector position sensor)
2. Mechanical problems:
* Worn friction discs in clutch packs
* Faulty solenoids
*Low or contaminated transmission fluid (ATF)
3. Hydraulic problems:
* Clogged or leaking hydraulic lines
*Low or uneven ATF system pressure
* Faulty torque converter
4. Engine problems:
* Insufficient engine power
* Incorrect operation of the engine management system
5. Drive problems:
* Worn or damaged CV joints
* Faulty driveshaft intermediate support (for rear-wheel drive vehicles)
Other possible reasons:
* Defective automatic transmission oil filter
* Damaged flywheel
* Incorrect adjustment of the automatic transmission selector cable
Diagnosis and elimination:
* Check ATF level and condition. Replace fluid and filter if necessary.
* Diagnose the electronic automatic transmission system using a code scanner.
* Check mechanical components for wear or damage.
* Check the hydraulic system for leaks, blockages or incorrect pressure.
* Correct any problems found and conduct a test drive to verify that jerking has been eliminated.