ClubLexus - Lexus Forum Discussion - How-To Tuesday: What's Causing Those Bad Vibrations?

Vibrations are not typically caused by an alignment. Note that I say typically, as it can occur, but it is not the norm. Speed-specific vibrations, AKA achieving a resonance frequency, are typically a tire and/or wheel thing. Road-force balancing is a very good way to test this, as the machine is able to detect anomalies in the tire and measure runout of the wheel, allowing you to easily chase down a bad tire or a bent wheel. That being said, if balancing the tires at a qualified shop does not work, your problem is probably on the chassis itself. That's where it becomes more complicated.
At this point the issue could be a driveshaft, axle, axle support bearing, tie rod end, control arm balljoint, control arm bushing, warped brake hat surface(typically caused by improper mounting of wheel by a technician. Make sure to cross-tighten the lugnuts snug, then cross-tighten to spec), alignment(again, not common), lowered vehicle, bad wheel bearing(this is an extreme, as the symptoms of a bad wheel bearing will usually present themselves in the form of horrible growling or grinding long before it causes vibrations), engine vibration(easy to isolate, just shift into neutral and see if the vibrations cease), deposits on rotors(rotors don't warp easily, despite what people think. The pulsing is caused by uneven heating and depositing of brake material), etc