I need a brake guru..
 

I can take apart an engine but when it comes to brakes I'm stupid. so this is on my moms car, 2007 bmw 328i sedan, (I know, not a max, but I'm sure all disc brakes are the same) on the driver side rear rotor, there is grinding. I don't know what is causing it. we need to get it fixed but I don't want to throw a new rotor at it and this just start as soon as it's back on. so can someone help me what's causing this?

what they're supposed to look like:Attachment 47941

driver side rear:Attachment 47942

I think you should remove wheel and inspect pads it might be time for some new ones / or there might be a rock .... I don't remember if this car has sensors at the pads

I would take out the wheels and check the pads. Like he^ said, there could be a pebble stuck somewhere in the pads.

yeah it has sensors in the brake pads so you know when the brake pads are almost fuly worn. thanks, I'll check it out. never heard of a rock causing this lol

Happened to many Lexus when I was tech
.... In fact happen to my max just a few month back

what was the cause?

That rotor is gone, looks like pads wore out. But what's strange is Bmer's have sensors in the pads that go off before the pads do damage to the rotor. Pull that wheel off and take a look at what's going on. How many miles on the car? Check all the brakes, not just that one corner.

yes and no... the sensor is either on the inside or outside brake pad... if he has a stuck caliper and one is wearing out faster than the other or simply stated the pad with the sensor on it is not wearing and quick as the other the light will not be triggered... I would check the pins to see it that are sliding freely and if the caliper is not stuck... its not unusual for a bimmer to wear pads unevenly

:sprint:

car has 63k miles. and I'm gonna take it all apart on tuesday

clean up the contact area for the pads with a wire brush and put some syl-glide or ford has some bomb dyelectric *sp?* grease on the pad contacts to caliper. make sure to lube up the pins too .. that rotor looks like its got hot spots which would indicate a frozen calilper imo. *we call that lot rot at the dealership :)*

what are hot spots? how do you see that?

Those are those dark spots on the rotors that occur from heavy breaking (correct me if I am wrong). I had those spots on my premium one rotors (don't know if they are any good).

Anti-seize makes an excellent brake grease.