What makes brakes wear like this?

Rotors rust while the car is parked outside. Ordinarily, the pads rub the rust off the next time the car is driven. But if it is parked for a long time, the rust can get thick and crusty enough that the rust eats into the pad instead of the other way around. As the pad is no longer flat, it doesn't touch the rotor in the rusty area and the rust expands.

A significant "ring of rust" will decrease braking performance and it is not OK to leave it.
 

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mk378 said:
Rotors rust while the car is parked outside. Ordinarily, the pads rub the rust off the next time the car is driven. But if it is parked for a long time, the rust can get thick and crusty enough that the rust eats into the pad instead of the other way around. As the pad is no longer flat, it doesn't touch the rotor in the rusty area and the rust expands.
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Blows my mind a bit that the rust is more "durable" than the rest of the rotor surface but this explanation makes as much sense as any.

I can feel "grooves" in the pad over top the rusty areas. Too bad the previous owner just did a pad slap.
 
In addition to the other right answers you've gotta USE your brakes once in a while. Some cars are biased so the fronts get most of the attention, so if you're light on the pedal all the time, the rears don't scrape themselves clean. Nor do they "jar" the pins or pad ears loose from developing stickiness.

My prii have done well with whatever programming splits between regenerative braking and normal friction. I hope the ABS gives them enough rear bias, too, but my rotors are staying clean. I do stomp on them now and again for good luck.
 
Looks like how the rear brakes looked on our fleet explorers in the mid 2000's as they aged... They did not see a huge amount of miles and seldom were washed, and fleet maint was not great... Narrow wear patterns on the rear rotors with everything sticking...
 
agarb said:
Sorry, my original post wasn’t clear.

Yes, at least 1 caliper pin is frozen and another is extremely dry. Pistons push in OK.

I pulled everything off last night so I could figure out what I needed to order. I decided to get a full set of pads with clips, rotors, and caliper pins.

The pads are the correct size but they aren’t wearing the entire surface of the rotor. I was trying to understand what causes this to happen. The rear brakes (rotors on the right) were the worst as SC Maintenance observed.

Also, the parking brake wasn't adjusted properly and didn't hold at all, not a good thing in a manual transmission!

But overall, the car is in great condition. Can't believe I was able to pick it up for $1200. Only one rust bubble above the left rear tire.
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Remember that you wipe off caliper pins. But if there is rust then replace. Don't sand with emery cloth or wire brush. Rust means the plating is going in the rusty spots so replacement is required.
 
One year here in the salt belt with uncoated rotors, maybe 2 and that’s what you get. The alloy they cast just isn’t what it used to be unless you break out your wallets and buy the best coated rotors available, they just don’t last. I buy Motorcraft from the local dealer. I asked them what they install for repairs and they set me up. The original rotors on my truck lasted 5 years/ 65000mi. I installed these last spring and at least on the outside through the wheel spokes, are looking great.
 
Lack of driving and midwest salt will lead to this in a surprisingly short amount of time.
It's just rust creep, sure you may have pins locked up due to lack of driving and other maintenance being neglected but once rust creep starts it's really tough to stop it. the rusty portion of the rotor is abrasive and wears the pad easily so it's very tough to get it to shine up again by just driving and using your brakes.

I have gone to extreme lengths and even wire-wheeled the area until it's smooth and painted those portions of the rotor to prevent rust until the pads wore into those areas again, but for the most part that is a fools errand.

Brakes on cars in the midwest.... if the sit outside.... use them or lose them!
 
Go to any used vehicle lot in the Midwest during winter and peek through the wheels. Every rotor you can see will be covered in rust, even some of the new vehicles will have it. Its called "lot rot" in the business.
 
I’ve seen flash rust on my vehicles simply from a summer rain. That’s the reason I suspect the alloy used in modern brake rotors is not very good. Combine that with road salt and you will have problems.
 
ElectroMechanoMan said:
I’ve seen flash rust on my vehicles simply from a summer rain. That’s the reason I suspect the alloy used in modern brake rotors is not very good. Combine that with road salt and you will have problems.
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Most brake rotors aren’t alloys.

Cast iron is what most rotors are made of. Purity of iron makes a big impact on corrosion, type of corrosion to be exact, as iron will corrode no matter what.

The purest the iron the less it will corrode, but instead from a protective oxide layer, like aluminum for example. Since brake rotors are wear items, there is very little incentive to make it out of high quality and purity iron.
 
agarb said:
Blows my mind a bit that the rust is more "durable" than the rest of the rotor surface but this explanation makes as much sense as any.

I can feel "grooves" in the pad over top the rusty areas. Too bad the previous owner just did a pad slap.
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What did you end up doing with the brakes on this Scion TC? I hope you replaced the pads and rotors, I'd love to see a comparison of new and the old pads.
 
Every spring I pull the wheels (around tire rotation time) and take apart the brake hardware, make sure all sliding surfaces still slide, caliper pins are greased. It’s best to remove the caliper bracket and get the rotor off too, I have zero desire for dealing with a stuck rotor when it comes time to replace. Doesn’t hurt to check the pad sliding surfaces in fall, just before winter, to make sure everything is still in good shape, I used to do all this spring/fall but it seems only “critical” to do in the spring, once the road salt usage goes down.

Good time to gauge the life left in the parts, determine if replacement is on the radar.
 
CharlieJ said:
What did you end up doing with the brakes on this Scion TC? I hope you replaced the pads and rotors, I'd love to see a comparison of new and the old pads.
Click to expand...

Yes, pads and rotors all around. There were two caliper pins totally froze up so I ended up putting a new bracket on one of the front wheels because it was totally filled with rust. I'm still waiting on a new bracket and caliper for one of the rear wheels to come in from Rockauto. That one was froze up so pad that I can't even get it apart. I can take a picture of the new and old pads for that wheel for comparison purposes.
 
I had this problem on a 1999 Chevy Silverado. Manufacturing defects related to the release powder used in the molds for the rotors is what I was told. GM replaced them.
 
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