I was having a horrible vibration/wobble with my truck this summer after I had dirven it for about 15 minuites and had braked a couple of times. Then turning onto a main road, I felt that horrible vibration around 30mph--and it got worse up to 55-60. Hard to keep it on the road. What it was--the front driver's side brake caliper kept trying to lock up! New claipers, rotors, & pads, (and $685) later, and all has been well ever since.