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Discussion Starter · #1 ·
New rotars put on in the spring. Are they supposed to be rusty.
The old one were worn down and bumpy looking, but I don't remember them
rusting like this. I can see the rust on my hub caps.
Brakes work fine.

Anybody...
 

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Could depend on what rotors and disc brake pads were installed.

Going back to the early days of disc brakes on cars, the rotors were made of heavy steel; in addition to their purchase price they exacted an operating cost -- lower gas mileage -- because of their weight, but rarely rusted on the working surface. It had much to do with the type of steel being used.

In order to reduce the cost of making the rotors, and the weight, manufacturers began to change the way the rotors are made by using different metals and processes. Today disc brake rotors are light compared to earlier, but because of their composition, are more prone to oxidation (rusting); some, primarily cheaper ones, more so than others.

In addition, the way the disc brake pads are made has also changed. Some now contain metallic powders. As the pad wears, the metal particles become embedded on the rotor surface. These particles, too, are prone to oxidizing.

The rust is more likely to show where it's damp (coastal areas, after a rain), especially on cars that are parked for a few days. On my car, the rotors stay pretty well bright and clear all summer, but in winter, when the car gets parked with snow and slush all around, the rotors develop the coating, sometimes overnight.

The rust usually is just on the surface, and it's scraped off by the disc brake pads after a few stops. Normally it needn't be of great concern. The dust does tend to get on the wheels. Even without the rust on the rotor, dust from the disc brake pads themselves tends to stick to the wheels. On cars that have disc brakes at the front, and drum brakes at the back, it's not unusual to see the front wheels coated with dark dust while the rears are clean.

If the brakes are working well, and the rust is gone from the rotor working surface after a few stops, there's probably isn't anything to worry about. If there's rust on the working surface even after driving and stopping several times, I'd have them checked.
 

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03 H6 OBW & 06 WRX Sportwagon
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I've had rust form on friction surface my stock rotors while I was at work! (in 8 hours)

not some tiny spot - all over and noticeable from 30 feet away.
 
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