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I'm having my car inspected (VT); its a 2014 BMW 328xi. The dealer is inspecting it and said there is a "heavy amount of rust on the inside of the rear brake rotors," and that they would have to turn them to pass inspection. The car brakes fine, there's no unusual noise or vibration or anything. This seems a bit suspicious to me; I've never had a car not pass inspection due to rust on the rotors, and the car isn't even that old. Does this seem legitimate, or are they trying to get some extra money out of me?

I had a chance to talk to the dealer; there's no pitting or anything else wrong with the rotor, and the brake pads themselves are fine, just what they are claiming is "excessive" rust. They said 2 hours labor, ~$200 to turn them.

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Resolution: Took it to a mechanic I trust, and it passed inspection fine. Said there was rust, but nothing where the brake pad actually hits, and no pits / grooves to worry about.

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  • I would recommend getting a second opinion. There are enough crooked mechanics around who cheat unsuspecting clients that it's always worth getting a second perspective.
    – anonymous2
    Oct 6, 2016 at 14:46
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    @anonymous2 I am; I have an inspection scheduled at another place tomorrow.
    – Andy
    Oct 6, 2016 at 16:22
  • Please provide a photo of your rotors. It's hard to answer without seeing the actual condition they are in.
    – Jason C
    Oct 6, 2016 at 17:33
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    @JasonC Added pictures
    – Andy
    Oct 6, 2016 at 22:06
  • Hm the contact surface doesn't look too rusty but I see nicks and gouging. The rust on the inside looks potentiality gnarly, although that's not on the rotor. The pitting on the outer edge suggests rust is deep. I dunno what vt inspection standards are like. I'd be tempted to get a new set of rotors / resurfacing, and pads if mine were gouged up like that. When's the last time you got your rotors changed? Another inspector might be more lenient than the first and pass you but you still might want to consider having some work done regardless.
    – Jason C
    Oct 7, 2016 at 0:34

3 Answers 3

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It would suggest to me that the rear brakes aren't contacting the faces of the inside of the rear rotors efficiently. The car is approaching three years old and bear in mind that brake rotors are usually just mild steel. Being under the car they are subjected to all kinds of road salt, water, mud, slush and grime. If you leave a car parked up for a few days you'll start to see the rotors rusting. This is swept away when the car is driven but if the pads aren't hitting the rear rotors properly, I could well believe they'd get fairly corroded.

Also, most braking is done with the front wheels. As much as 85% of braking is done by the front of the car which is why the front brakes are typically larger with beefier calipers and pads. If the rear brakes were below optimal efficiency, there is a chance you may never notice.

I'd suggest going and taking a look yourself. It should be very easy to see either shining a light under the car or using your phone with the flash on to take a video with your arm extended if you can't fit your head under the rear of the car.

If they are corroded, I'd suggest having the rear caliper slides lubricated and adjusted as appropriate at the same time the rotors are turned, otherwise they may corrode again fairly quickly.

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  • Assuming the dealer's technician isn't full of BS, is ~$200 (2 hours labor) about right to turn them?
    – Andy
    Oct 6, 2016 at 17:09
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    @Andy That seems reasonable. It would be weird for the dealer to bs you about rotors btw, if they were going to trick you during an inspection for some mysterious reason, they'd do it with something you couldn't easily see or check. Despite inexplicable common belief most technicians are real people who care about their work, like you or me... with allowances for an honest mistake or personal judgment here and there. In a salty place like vermont esp if you dont check your rotors on the regular it's completely reasonable for them to be highly corroded.
    – Jason C
    Oct 6, 2016 at 17:35
  • I've had shops try to pull this before, saying rotors were bad for some reason or another. I had another dealer for my Acura try to say a support was rusted and could fail and the engine would fall out "within six months." (And then oddly forgot to mention it over numerous other services for two years.). Needless to say I didn't go to them for my next car. I think they are trying for something that isn't covered under the maintenance warranty (which even covers wore brake pads). At any rate, I've add some pictures.
    – Andy
    Oct 6, 2016 at 22:10
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    @Andy Rotors are sort of a judgment call though. Many people's opinion about the same rotors will vary. Same with rusty metal in general. More likely than somebody trying to trick you, you're just running into different judgments. It is a very fuzzy field. If two shops tell you different things, more often than not its just different judgments, rather than the one-whose-opinion-you-like-least intentionally bsing you. Not always of course, but most people arent out to get you. :) You could try until you find a more lenient inspector but your rotors look pretty worn to me. Others may disagree.
    – Jason C
    Oct 7, 2016 at 0:41
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    Accepted, although a second place passed them the way they are. Maybe in a year some action will be warranted, but the lease will be up by then.
    – Andy
    Oct 7, 2016 at 12:51
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im a nys inspector and i fail for rusted contact surfaces all the time. in your case from the pics i would not fail that rotor. BUT i haven't seen the inside of the rotor either. 99% of the time the outside looks alright its not until take a look at the inside you find they are hammered. my rule of thumb is if 50% of 1 side of the rotor is hammered i will fail it. but every inspector is different. its their license and their discretion.

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All brake rotors always rusting because they must be made from high carbon steel. Some coating or painted help but only cosmetic matters. The main point is hardness, and deformation resistance to heat and pressure. Nothing else matters. Brake pads should wear the rotors evenly, no deep scorrings, 1 or 3 thin scoring lines are normal from trapped stones or road debrees.

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  • There's no need for your last paragraph.
    – Andy
    May 25, 2020 at 14:33

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