2002 Other Nissan Models

Shakes or Wobbles problem
2002 Other Nissan Models 4 cyl Two Wheel Drive Manual 80 000 miles

At certain speeds in 6th gear there are vibrations, example: between 60 and 65 KPH, when accellerating and decellerating and the same with speed between 90 to 95 KPH. Also this happenens in other gears, but not as severe. In order to try and recify the problem, the gear box bearings have replaced, also engine and gear box mounts. It has been fitted with a damper on the drive shaft. Please advise.