BlueHorse

Hi, folks,

I replaced my factory rotors/pads on all 4 wheels 6 months ago, with non factory drilled slotted rotors and ceramic pads (very low dust). The braking power since day one was weaker than before, which to some degree is expected as slotted/drilled rotor has less surface area, and low dust pads do not work as well as dusty ones.

However, I noticed this strange humming noise coming from front side every time I do a hard or medium brake. It is not engine noise as I can't hear the humming if not in braking, AND first time I heard this humming was right after installing new rotors/pads. The sound is in low frequency, does change slightly lower as car slows down, and it is not the high pitch squeaking sound which you hear when pads are near its end of life.

Is this humming due to some kind of vibration of the front rotors?

The first two photos attached show some straight line markings on the front rotors. They are approximately in parallel with the slot, or intersect at 90 degrees with the slot 90. But on the rear rotor, shown in the 3rd photo, no such straight lines observed, only circular ones. I have looked at neighbor's Mercedes Benz, and don't see such cross markings on its front rotors.

Is there something wrong with my front braking system? Maybe loose caliper, rotor, or pads? I thought I made sure rotor screws were all right, and calipers were all tightened, and all parts holding the pads were put in carefully.

Can't be rotor material is different between mine and my neighbor's, right? Because my rear rotors were from the same vendor.

Pls help.
Thanks!

Gee_115

I'm not an expert but it definately seems like there is some abnormal wear on those front rotors. You should probably get them machined and change the front pads. That's if you don't want to pay to get them replaced.

Hyper_545i

Silly question, but did you follow the break in procedure for the pad/rotors after installing them? Was the sensor installed properly? From the scrathes on the rotor, something appears to be making contact with the rotors, other than the pads. Debris? I would check the speed sensor. I had a similar issue, not with vibration but sound when the brakes were applied. I mentioned it when I brought the car in for service and they had to "adjust the speed sensor". Good luck and keep us posted.

best1

looks normal to me!!

balbs

+1...Also when hard braking that humming or low-end zipper sound is normal. If you think about it there are those ridges and dips on the rotors from the slots and cross-drilled holes that temporarily not touch a certain part of the pad for awhile that causes the noise. You generally won't hear that low zipper sound on plain blank rotors.

onetime

Those cross hatch marks on the front rotors appear to be from machining.

BlueHorse

These lines are crossing each other. Wandering how the machinning process could cause this X shaped marks?

Rotors were new, and probably just 2~3K miles on them. And I never machined them...

Should have gone to a blank rotors...

Still struggling to understand these marks and what to do. Pls share more of your thoughts.

Thanks!

BlueHorse

But that does not explain the X marks on my front rotors... my neighbor's Benz uses drilled/slotted front rotors too but I don't see any X marks.Thought?

balbs

Each manufacturer has their own way of doing things. I'm sure those are just tooling marks. Maybe from the last sanding\polishing process maybe from a belt or some sort that makes the lines straight and done in oposing directions. Mine had them brand new and they start to fade away with use. I'm sure it's the same with your neighbor's Benz.

BlueHorse

I just thought about this - the X marks are aligned pretty close if not precisely with the upper and lower edge of the brake pads? If so, what does it say about my braking systems?

The rear rotors came from the same manufacturer, and same model, and so far no X marks at all. Don't think there is any debris. The front rotors did have some deep circular groove, which maybe another reason my braking power is weakened.