Mitsubishi Repair: Bad Shaking 97 mirage, tie rod ends, mitsubishi mirage

Question
Hi I have a 97 mitsubishi mirage and it shakes really bad. Not so much when going slower but especially on the interstate or hwy. It is so bad at times the passenger seat shakes and the doors too(so much that top of door jam looks like it is coming away from the car). Sometimes it seems worse than others but when I let off the gas it seems to stop shaking. We have checked all the tires, changed the tie rod ends and the front hubs and it still does it. Also checked the back hubs. Not sure what it is!! Think its coming from the front but have checked alot of things but the car shakes/vibrates so violently that the whole car shakes so not sure if its the front. Bought the car almost a year ago. Havent had any real problems with it. Do live in a place where water gets high sometimes have to drive through it. Also,boyfriend driving car and missed a turn and went into kind of a dip going approximately 40 mph. Car was fine for a while after that so not sure if that makes a difference. Also needed to change tie rod ends for a while and didnt. Would appreciate any and all suggestions you have. Thank you so very much for your time and answers cuz i can't find anything on this. KIM

Answer
Kim,
The most common causes of vibrations at high speed is poor wheel alignment and balance.  If the wheels are out of balance due to damage, then you'll continuously have poor performance, premature tire wear, and bad vibrations.  When a tire shop performs a spin balance on a wheel, they usually simulate the wheel spinning at around 35 mph.  So you may have a slight problem in the wheel that makes the car vibrate at a higher speed.  Other causes for vibrations can happen with bad shocks, struts, and coil springs; mainly suspension problems.  

A worn engine mount can also cause shaking.  This may give clues as to why the shaking stops when you let off the gas.  Your Mirage may also have a balance shaft that is damaged or a balance shaft belt (related to the timing belt) that is worn.  Have your mechanic inspect the belts, shaft, and engine mounts to see if the problem may be there.
Good luck!