meng,You say you have just purcahsed the car.How is the overall condition of the car? Has it been restored? Or just a daily driving car? Performance up grades? .Please give a little more info.Any pictures? It sounds like the springs are worn out.I had a 1965 Dodge dart.Even after swapping the 6cylinder engine to a 8cylinder and I also replace the rear springs.I could have three people in the car without a problem.Please more information.