My 1999 Jeep Cherokee (4wd, but not engaged when this problem occurs) shudders terribly when I accelerate while merging onto the highway, between 55 and 60 mph. It’s worse if I’m on a curving on-ramp or hit a small seam or bump in the road. Usually it smoothes out as I accelerate past 60, but sometimes the only way to stop it is to brake hard – not a good move when merging onto a highway with traffic behind me! My mechanic recommended new tires (the old ones were cupping, which he thought caused the problem, although I thought it was a symptom, not the cause). The new tires helped for a while, but now the problem is back. I’m avoiding the expressway and searching frantically for a diagnosis. Help!
BTW, the jeep has 70,000 miles.
does it shudder @ all when the vehicle is idling in neutral and you rev the engine?
If the answer to roushus’ question is “No”, then I’m going to guess that you’ve got a worn / destroyed ball joint or tie rod end.
If the tires are cupping it means the shocks are worn. If installing new tires eliminated the problem for a while, and now the problem is back, it means the new tires are beginning to cup because of the worn shocks. I’d install new shocks and see if that fixes the problem.