My 1998 Contour shudders, on then off, on then off... when driving at about 65mph. I just replaced the timing belt and it runs smooth at lower speeds and at idle. What could be the problem?

Is the shudder from the engine or the car itself?

That's a good question. It's hard to tell as it is only happening at higher speeds. It doesn't feel like the whole car. And I would think, if it's the tires or alignment, it would be constant. But it isn't. It starts, lasts for about three seconds, then stops. Then about three or four seconds later it will do it again. And this will continue until I slow down or stop.

Could be a wheel bearing or CV joint issue. At a certain speed the bearing or CV joint hits it's resonance frequency and can cause an on again and off again vibration from the part being worn.

Thanks. I'll look into it and let you know.