All three engine mount bolts broke on this car and were repaired. The car shudders when it gets above 45 mph and it gets worse as the speed increases. The mechanic says that if it was caused by the engine being mounted wrong, you’d be able to make the car shake when in neutral. He says the tires are the culprit. I took it to the tire dealer (the tires have fewer than 9000 miles on them) and he says he put a new set of tires on the car and it still shakes. What else could be causing the problem?
first it would help to know something about the history of the shudder and the broken mounts. replacing mounts on a '95 is not an odd thing to have to do, but did the mounts all literally break? or were they just worn out? did it shudder before these were replaced? or did it start after? your description is cryptic.
in any case, if the problem was with the mounts the shudder would not wait until until 45mph and would likely be most associated with acceleration, not speed. i would tend to think that the mounts are not the problem.
if it is a higher speed shudder then the tires are, in fact, the first place to look - a basic check of the balance would be good. but from there, there are a very large number of causes including bent rims, worn front end parts, suspension problems, wheel bearings, etc. etc.
you need not only a good tire place, but a good alignment/front end shop to go over everything.
All three mounting bolts were cracked and replaced. The car never shook before this problem. I had the car at the Firestone service center (where I bought the tires) and they aligned and balanced the tires twice but the shaking still persists. The mechanic who replaced the engine mount bolts says he detected “bumps” in three of the four tires, suggesting they are out of round, but the manager of the Firestone center said the current tires are fine and not the problem. The suspension, axles and rack and pinion are all recent and there is no sign of anything wrong with the body. I still think it’s the tires. Should I take the car to a second Firestone dealer to see what they say?