Talking about non perforated brake rotors, on a VW gol, today it appeared to have 2 perfect small holes, which don't seem to align with anything. It seems to be corrosion, but the interesting fact is that they seem to be really perfect.

  • What can cause this?
  • Can the car still be used with this, or is there any risk involved?

enter image description here

5 Answers 5


These are stomata (gas bubbles) in the cast iron or cast steel of your brake rotors. Stomata are usually perfectly round, but may be teardrop-shaped. They are sometimes not visible in the original casting but appear when the surface is machined or, as in your case, worn down. They are a sign of poor quality control at the foundry.

See this link on casting defects for more information.

Example of stomata in casting: enter image description here


It looks like the car sat for awhile in the past and the (worn) pads developed rust. The rusting rivets on the pads probably ate those holes into the rotor. Look at all the other rotor surfaces. Brake linings can absorb moisture and cause rust on touching steel. I have seen clutch lining rusted tight against a flywheel. It is safe, but your rotors overall look poor.

  • It does look like it could be an electrolytic reaction between the rotor and the brake pad rivets. It does seem odd that there are only 2 and in those positions. Also the rotors seem in otherwise good condition,
    – HandyHowie
    Mar 27, 2022 at 8:39
  • This is an interesting theory. Although I think these brake pads don't have rivets in the part that touches directly with the rotor Mar 27, 2022 at 21:45
  • Rotors have a specification about minimum safe width. It seems time for this to be checked and measured. Mar 28, 2022 at 13:16

Too "perfect " for corrosion. Some rotors have holes drilled in them for cooling , so it is unlikely that the depressions would cause a problem. A couple applications of the brakes will clean off the superficial rust. Although the surface looks uneven like worn pads.


What can cause perfect holes in brake rotors?

Neglect or intentional drilling by the previous owner.

Two more seem to be starting.

Overall, the rotors appear to be in poor condition. If this car has been sitting or if you just bought it from someone then it probably needs a brake job.

You should take off the wheel, remove, and inspect the brake pads.

enter image description here


Vehicle tyres can have pits moulded into them like this, used to show when the item is worn down to its safe limit.

However I've never seen one on car brake rotors - the edges would erode one's brake pads and they're not in a location that is easy to inspect.

  • 2
    Not likely the edges would cause a problem, as some high performance brake rotors have holes drilled in them for heat dissipation.
    – nasch
    Mar 28, 2022 at 23:38
  • 1
    Would souch wear indicators be necessary? I always used that lip that develops around the outer edge as a gauge of "how worn is my rotor?"..
    – Caius Jard
    Mar 29, 2022 at 8:30
  • 1
    @CaiusJard "Would souch wear indicators be necessary?" I always used calipers to measure the thickness of the rotor and compare with the specifications to determine whether they were still serviceable or not.
    – Glen Yates
    Mar 31, 2022 at 22:40

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