Warped Rotor or dirty flange?
 

I just put new rotors on the back of my 300E this weekend. I replaced the front rotors some time ago and corrected my pulsating brake pedal at that time. The pedal started pulsating again recently, and it started occurring shortly after I let a rear pad get into a rotor. After I replaced the rear pads the pulsting started shortly after that. I assumed the problem was in the rear.

Here's the question. Could it be because I did not clean the flanges when replacing the rear rotors? If this is not likely, I will probably replace the front rotors. If it is possible, I guess I'll have to use a dial indicator to find the culprit. Back when I replaced the front ones, I tried the dial indicator and it didn't tell me much. I replaced the front two, and the problem went away.

Thanks,

I ALWAYS clean the hub and apply a little bit of anti-sieze to it. This will keep the rotor floating on the hub.