What are these dark spots on my front rotors?

[Klutch9]

This is on our 2016 Explorer. Trying to chase down a braking vibration at higher speeds. Just replaced the rear rotors and pads, so I know those aren’t the issue. The pictures here are from the fronts. They were replaced about 3 years ago (pads and rotors), and the wear is actually very even on both sides. The slide pins and pads move freely as they should and brake fluid was recently flushed so that’s not an issue. But the inner diameter portion have these blackish deposits it looks like. Are these pad deposits? When I replaced the rear brakes a couple weeks ago I did a proper bed-in procedure, and it didn’t touch these black spots on the front. I want to replace the rotors but don’t want to just throw parts at it.

 

[Pew]

That's a bit of runout; the dark spots is where the pad isn't contacting the rotor face properly - probably the source of your vibration issues.

 

[wag123]

Pad deposits. The number one cause of brake vibrations.
Replace the rotors and pads and bed them in carefully.

 

[Klutch9]

Pad deposits. The number one cause of brake vibrations.
Replace the rotors and pads and bed them in carefully.

Can I just clean up the rotors on my wire wheel? (Not handheld, bench-mounted). Then I’d sand the pads down and re-bed.

 

[wag123]

Can I just clean up the rotors on my wire wheel? (Not handheld, bench-mounted). Then I’d sand the pads down and re-bed.

No, but you can have them turned if there is still enough material left. New rotors are so cheap that you are probably better off just replacing them. Always replace the pads when you turn or replace the rotors.

 

[Astro14]

I would just replace them. Even rotors made in Germany are about $60 for some of my cars. At that price point, easier to replace than turn and hope…

 

[nascarnation]

Before I replaced any parts, I'd take the vehicle out to a location w/o traffic and get them good and hot. Maybe half a dozen consecutive stops from 60mph. Then just drive for 10 mins to cool things off.

 

[wag123]

Before I replaced any parts, I'd take the vehicle out to a location w/o traffic and get them good and hot. Maybe half a dozen consecutive stops from 60mph. Then just drive for 10 mins to cool things off.

If you are going to try this you should not come to a complete stop. Coming to a full stop with very hot brakes is how pad material is unevenly transferred to the rotors.

 

[Klutch9]

Before I replaced any parts, I'd take the vehicle out to a location w/o traffic and get them good and hot. Maybe half a dozen consecutive stops from 60mph. Then just drive for 10 mins to cool things off.

I have already attempted to bed these in again when I bedded in the rear brakes recently. Didn’t make a difference.

 

[SubieRubyRoo]

Can I just clean up the rotors on my wire wheel? (Not handheld, bench-mounted). Then I’d sand the pads down and re-bed.

I’ve seen it said a couple times, and seem to have confirmed myself, that if you get out on a country road and do several HARD 60-5 or so brake applications (but do not stop!) and get the pads and rotors very hot, that if it is pad material or slight mating issues that this will help clean it off and restore smooth operation. It obviously won’t help runout or damage.

But the key to remember is, at no time during the 60-5 braking, do not come to a full stop and allow at least 5 minutes cooling time before coming to a full stop so that the pads do not put material back onto the rotor.

 

[PontiacHO]

Rough cut rotors tend to show the same as well as super hard metallic pads.

 

[vavavroom]

Looks like cementite formation to me.

 

[Klutch9]

Well, whatever the issue is, I've decided to just replace the rotors and pads. Truthfully, I've never liked the pads that were on there anyway, they dust way too much; its black dust too. Maybe that had something to do with the black sections on the rotors? Who knows.

 

[nascarnation]

I have already attempted to bed these in again when I bedded in the rear brakes recently. Didn’t make a difference.

Bummer. FWIW I've had good luck with Akebono pads. Not sure about rotors these days.

 

[walterjay]

I recently installed Bosch rotors and Wagner Thermo Quiet pads. The combination has been outstanding on my SantaFe suv.