Nissan Fairlady Boot Damper problem

hey guys,

i have a problem with my car.. the steering vibrates excessively from about 90km/h onwards.. i have changed new tires.. rims checked not bent, alignment and balancing done.. what else could be the cause of this? btw after doing alignment and camber alignment the vibration got stronger.. my car set up is 4agze custom made driveshaft on the left side to correct length but same spec as ori gze shaft.. right side is original gze drive shaft. bearings are relatively new.. hope someone...