I bought new tires balanced them & aligned the car. Everything was good then at some point I changed brakes (calipers & rotors) then I changed the trans. mount to a poliutherane, then I ran over a nail & had to fix a tire. All of this around the same period & then noticed that past 70mph the car starts to shake & by 90mph Im afraid that the car is going to fall apart.
Now, I dont know how any of this could affect the balancing but I cant think of nothing else. by the way the tires are going to be 1 year old pretty soon. Any ideas?

From what I read: all OK until poly trans mount, new rotors, and a flat. If the poly trans mount has a plate that is fit underneath of it remove that first. This seems to be a common problem with a particular manufacturer. The plate changes the driveline geometry and causes vibration. Removing this 'stiffening' plate restores the driveline geometry and the vibrations go away.

The next easiest would be to have the tire that got a flat re-balanced. The shop may have plugged or R&R'd the tire for an inside patch and didn't rebalance it. It is also possible the tire had cords damaged and is no longer round. Only a tire replacement will fix this.

The rotors can also cause problems. Seems some 'off-shore' rotors aren't balanced. _At all_. To check these it will cost some grease seals. Pop the grease seals out of the rotor, use a thin oil on the bearings (can use the old ones if still in decent condition), and place them on the spindle with just a light touch on the spindle nut.

Does the rotor stay where it is located? Or does it always spin around and settle in the same location? Same location then it is out of balance.

RBob.

thanks for the reply! I was thinking it were the rotors, but I guess it will be best to balance the wheel first & see what happens. I will check the trans. mount tomorrow but I dont remember no plate.