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Let's say you take off the wheel (when replacing the pads, for example) and look at the brake rotor. What are the signs that it's time to replace the disc?

Let's stick to clear visual signs that don't need extra special equipment or driving the car and listening/feeling to notice, such as slight warping.

A couple of examples that come to mind:

  • Scoring

Bad

  • Cracks

Very bad

  • Low thickness

What's depicted here is not necessarily bad

What else? Is rust dangerous? Even if you have a single sign to add, don't hesitate.

Example pictures along with written signs would be extra helpful!

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  • Some people will just replace the rotors whenever they change the pads because on some cars they are so cheap it's not worth the time or hassle to take them and have them turned.
    – JPhi1618
    Commented Mar 25, 2016 at 17:05

2 Answers 2

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Overheated rotors can show some tell-tale signs. Once the metal has been overheated, it can weaken or warp which are both bad things. Some signs:

Bluing

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Cracks

These "spider cracks", "heat cracks", or "heat checks" are only on the surface of the rotor, but are still bad.

enter image description here

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  • Indeed! Though does it always mean that the rotor is warped if it has bluing? What if it has such overheating signs, but shaking doesn't occur when braking hard, should the rotor be replaced anyways? Does it lead to cracking?
    – I have no idea what I'm doing
    Commented Mar 25, 2016 at 14:38
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    Bluing doesn't always mean the rotor is warped, so to your point, it probably doesn't mean the rotor always needs to be replaced. I would look at it as "a visual reason to consider replacing or fully inspecting the brakes". If you have bluing, something went wrong or the car is being driven beyond its abilities.
    – JPhi1618
    Commented Mar 25, 2016 at 14:43
  • @JPhi1618 - Great comment and spot on.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Mar 25, 2016 at 17:35
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The previous poster have great examples of rotors in need of replacement but I worked as a mechanic for years and rotors have become so cheap for most vehicles the easiest thing to do is replace them as paying someone to resurface often costs more on labor than buying new rotors. The most common symptom is shaking in the steering wheel when braking from high speed.

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