Possible reasons for the shock when engaging reverse gear in the automatic transmission:
Transmission problems:
* Worn or broken planetary reverse gear
*Damaged reverse friction discs
*Low or contaminated transmission fluid (ATF)
* Faulty reverse solenoid valve
Engine problems:
* Low engine idle speed
* Engine management system malfunction
Differential problems:
* Wear or damage to differential
* Insufficient level of transmission fluid in the differential
Other reasons:
* Faulty gear selector position sensor
*Weak or worn engine or transmission mounts
* Clogged transmission fluid filter
* Transmission fluid that is too viscous or incorrect