I took my mom, 2 nieces and my sister out for a drive. My mom and my 2 nieces (combined weight of about 375 pounds) sat in the back. My sister and I sat in the front. I had barely started to drive and pick up speed (40 mph) when the hood looked like a washing machine (when it starts shaking) and the whole car started to shake. I slowed down and it stopped, I picked up speed and the shaking started again. I then dropped them off and had my father drive it. He drove it fast and slow and for at least 15 minutes and not one time did it shake. He said I would probably have to put heavy duty shocks in the back. I never remember this happenening, I had the front end rebuilt in May. Has this happened to anyone and what did you do?
Thank you.

This is just a theory, but here it goes. With the extra weight in the rear caused a change in the pinion angle. So perhaps you are experiencing some driveline vibration?

Just a thought.

Andrew

Check your u-joints. I bet at least 1 is binding.