My comment about the proper name of the measuring device was only to inform. I' have no idea of your experience or knowledge. No offense was intended nor was there any implication that not calling it by the proper name meant you were ignorant about warping vs. contamination.

FYI: In my profession we call it by what it actually is. If we called every precision measuring device a mic, we'd create a lot of confusion. So, they are called specifically what they are.

 

Ok, by question is this problem only happens when front rotors are bad, or can it happen because of bad rear rotors too? At 46kmiles i figure ima need front rotors and pads soon, but i just changed the rear brakes 500 miles ago

 

If the problem with the rear rotors is one where the coefficient of friction on the surface of the rotor varies around the rotor (due to contamination or uneven pad material transfer), then you'll likely never know it exists. You won't feel it through the pedal and it won't affect your steering because it's on the rear wheels. It would have to be monumentally bad for you to notice it.

However, if the problem with the rear rotors is that they're warped, you'll likely feel it as a pulsing (to one degree or another) at the pedal.

 

So quick update: the front lower control arm bushings were shot, both were replaced and the vibration is gone