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Some years ago I replaced the stock rotors for slotted and drilled on all four wheels of my 2003 Monte Carlo. At the time I needed to replace the rotors and they had a habit of warping. The new rotors work great and way outlasted the old ones without a hint of warping. However, after putting them on my car (along with new pads) I started having rings appear on them like this:

enter image description here

This picture is from the front wheel, I have one on the back wheel that is mostly rust ring with 2 small normal rings. I have considered replacing them but I have not had any impact on braking performance (even with the few times I have had to stand on the brakes) or funny handling in all types of weather.

I have changed out the pads once thinking it would clear these up, but no luck. I don't know what the insides surface look like either. I'm in need of new brake pads now and wonder what I can do to improve this situation. I have read up on turning the rotors and know what it takes to do it with slotted and drilled ones. I barely drive this car as it is and they are not warped so that is a last resort at best.

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Sorry, but the rotors are the problem.

It would seem like the edges of the holes stick up a tiny bit. The rotor is a much harder material than the brake pads. These edges dig out grooves in the brake pads so it can't contact the rotor at other points in the rotation and provide braking force/rust removal.

Zoomed in ASCII art:

  Pad        ---- < Groove
-------------    ------------

-------------|  |------------
  Rotor      |  |
-------------|  |------------
                ^ Sharp edges

I'm somewhat surprised you haven't noticed a loss in braking power. You have like 40% of the designed area actually making contact!

In my personal opinion, slotted and drilled rotors aren't worth much on a street car (not race car). But put 10 mechanics in a room and you'll get 11 opinions.

  • It varies across the wheels, and I'm only looking at the outsides of the rotors. The other side of the car looks much better. One of the back wheels is real bad though where the normal is only 10%. I agree that these don't make much difference for a street car, but given how easy the OEM ones warped and this was the same price, it was a no brainer. – BPugh Sep 22 '15 at 14:12
  • Might be the way I drive anymore as well in an effort to save money: less hard acceleration, braking, and using the cruise just about anytime. I have better things to spend money on than commuting. – BPugh Sep 22 '15 at 14:19
  • Just say no to cross-drilled rotors for cars. Slotted, if you absolutely must, but you pay a price in brake pad life for sure. – Brian Knoblauch Sep 22 '15 at 15:33
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I'd be tempted to skim them on a brake lathe (or have them skimmed on a brake lathe if you don't have access to one yourself) and fit a fresh set of pads.

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