While changing my brake pads today, I found that the right front rotor was completely loose. The only thing holding it on was the caliper. When the wheel is lugged down, the rotor is snug tight. But what caused the rotor to break loose?

 

there are like that

 

like he said. That is the way they are meant to be. Its not going to go anywhere

 

Yeah I'm not too worried about it as it is snug with the wheel on. But the other three are snug all the time, causing my concern. Thanks.

 

The rotors get rusted on after a while which is the reason why they can be a pain in the a$$ to get off. Your one rotor was probably just not rusted sufficiently to hold it down. The only thing really keeping the rotor on is the wheel. All of them will just come off with no wheel if you pull hard enough.