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Short question - would you replace this rotor?

enter image description here

The 'rust band' on the outer edge of the rotor is part of the 'braking surface' - in other words, if I lay the pad on the rotor, part of the pad braking material is on top of this rusted band. You'd think the pads would wear down the rust and keep it clean and shiny, just like the main shiny braking surface.

Long question: what's going on here? How come the pad isn't removing the rusted band? Would running this rotor with new pads cause the pads to groove and wear out prematurely?

  • What do the other rotors look like? – 3Dave Apr 21 '20 at 0:54
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Replace the rotors and pads. I wouldn't attempt to turn or resurface rotors in that condition. (Honestly, it's rarely worth the minimal cost savings to turn rotors, in my opinion.)

If the other rotors have the same uneven wear pattern this is likely a characteristic of the braking system on your car. Without seeing the pad and the rotor, it's impossible to really tell what's going on there. If the profile / cross section of the pad is uneven, then it may not be applying sufficient force in the problem areas to wear away the rust. If the rotor is sufficiently worn, weird things will happen to the pads. This can be one of the side effects.

Another possibility, all be it a long shot, is that the rusted area is actually lower than the shiny area. In that case, the pad wouldn't make contact. I'm not sure how that would happen as I've never seen a rotor with a bevel. BUT, I have not seen all rotors.

I'd like to see what the back of that rotor, as well as the others on the car.

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That rotor may be usable, it may look ugly but it actually has nothing to do with the lip on the outer edge. What's happening is that the pad is removing material from the part of the rotor it contacts, its contact area is little bit in from the outside so it leaves a bit of material. That lip is on the large side, but isn't a problem.

The main question is whether the worn area is still thick enough to be in the tolerance specified by the car manufacturer, and for that you need a caliper. If it is reasonably above tolerance and not warped then you can use the rotor. I personally would shave off that lip by putting it on the car, spinning it and using an angle grinder to sand it down gently. If it is below tolerance then it needs replacing (do both sides). If it is still above but getting very close to tolerance it's a judgment call - you have it all apart now so it's easy.

  • So to clarify, the rust band IS within the part of the rotor that the pad contacts! I realize most rotors will have a thin band on the very outer edge which is outside of the pad contact area, which rusts - that happens to all rotors. This one has a rust band that extends into the braking surface, so the pad IS sliding over it, but somehow not cleaning it off! – wild coast Apr 20 '20 at 16:57
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    That doesn't make sense tbh. – GdD Apr 20 '20 at 18:00
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I would just clean/cut down the wear lip on the edge. The shop manual , or maybe on-line, will give the minimum thickness for the rotor. A shop will say "replace it". I have removed the edge by jacking up the car, place the bare rotor on a wheel and run the engine- turning the rotor. I use a coarse file. If you don't feel comfortable doing this, don't do it.A local shop should turn down the rotors for several dollars ( if you carry in the bare rotors), the shop likely also has the minimum thickness information.

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Take the rotors to a shop that turns rotors and have them measure the rotors to see if they are within specs to be turned. They should also make sure they are true and not warped. I do not see any reason that these would not be able to be turned and reused just because of the rings. More often than not, the pads do not make contact with the entire face/surface of the rotors, so this condition can be a common occurrence. You can also double check the owner's manual or the maintenance manual to make sure that the rotors and pads are the proper sizes. Often times you can have more than one size for the same model year vehicle, especially on trucks or performance type vehicles. Or someone replaced the rotors or pads with the wrong size the last time it was done. But in all honesty, this is not a bad looking rotor.

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