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I need to replace my rear brake pads. A mechanic suggested I also replace my rotors because they are rusted around the edges. The rotors are in fact quite rusted, however, there is no rust on the actual surface that touches the pads. Running my fingers over the surface of the rotors, there does not appear to be any buildup of brake pad deposits and the surface is relatively smooth. There is however one small circular scratch around one of the rotors. While the pads are ready to be replaced, they are still within standard tolerances, so it's not like there is metal-on-metal going on. The mechanic warned that replacing the pads without replacing the rotors at the same time would be a waste because the rusted rotors will just eat up the new pads. I find that hard to believe given that the rust is just on the extreme edges of the rotors, which are parts that do not appear to touch the pads. The brakes do not appear to make any abnormal noises at all. Therefore, according to this post, it doesn't seem like the rotors need to be replaced.

Is rust on the parts of the rotors that do not touch the pads enough to require replacement? Is there a way I can tell on my own if they need replacement?

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Pro-tip: mask off the faces of the rotors with masking tape and newspaper, then apply a couple of coats of high-heat Rustoleum (or similar) to prevent rust. This works quite well for brake drums or any other piece of metal that's prone to rust. Just don't spray it on your exhaust because it will cause your exhaust temperatures to increase above safe levels. –  Juann Strauss Dec 8 '14 at 9:10

10 Answers 10

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It's not required that you replace your brake rotors at the same time you replace your brake pads, but there are many reasons why it's highly recommended.

Primarily, it's not the rust you should worry about, there most likely always going to be some rust around the edges, that's not at all out of the ordinary. The main problem is that your rotors are most likely grooved, and putting fresh pads on grooved rotors is going to wear the pads faster. Using those grooved brake rotors could also cause your wheels to wobble once you add new brake pads.

This is one of those instances where it makes more sense to spend a little more money to eliminate the possibility of a huge headache down the road. It's up to you whether you want to gamble.

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Is there a way for me to inspect the rotors myself to determine if they are grooved to the extent that they require replacement? –  ESultanik May 29 '13 at 0:37
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To clarify, the grooves themselves won't lead to wobbling. However, old grooved rotors are more susceptible to warping due to heating, which leads to a uneven braking (sometimes called shuddering, sometimes called wobbling). –  Brian Knoblauch May 29 '13 at 12:14
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The minimum acceptable thickness will usually be stamped on the brake rotor near the center. You can use a micrometer to measure the thickness of your rotor. Be sure to measure in different spots ( the grooves for example). youtube.com/watch?v=NpkoffI1co4 –  hillsons May 29 '13 at 17:43

If your rotors are thick enough and there are no defects in pads area (big grooves, buldgy edges) I would not worry at all. There's no need to replace rotors each time.

If there are some defects that can be removed and the rotors are thick enough - consider resurfacing the rotors, that might be cheaper.

All-in-all, given that the only downside is faster pads wear I would not bother as pads are generally quite cheap.

I my case set of pads and labor to replace them is almost twice cheaper than replacing rotors. So I would went for another round replacing only pads.

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It has been my experience lately, most rotors are not worth turning or resurfacing. Most resurfaced rotors are so thin that they tend to warp quickly even if thicker than the minimum thickness spec. –  mikes May 29 '13 at 10:36
    
I just did the front brakes on my car this weekend, and I noticed that the allowable rotor wear was only 2mm. I think resurfacing them after a normal amount of wear would probably take them over the limit. I tend to just replace them every other pad change -- they're not that expensive, considering how important they are. –  TMN Jun 3 '13 at 15:32

you don't really need to replace the rotors unless the thickness is below the specs and damage to them can be seen with the naked eye. Your mechanic just want to make a bit more money. Brake rotors can last up to 100,000 miles on average before they need to be changed. This is what I suggest. Google " what is the average lifetime of brake rotors " and you will get a lot of sites with very useful information that will help you make up your mind. In your case, you have not provided enough information to get a meaningful answer. It all depends on how long they have been in use, how you drive, how often you change the pads...

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Can you feel or see deep grooves? Are your old pads irregularly worn? Have you already resurfaced the rotors? Do you feel shudder under braking? Are they close or under minimum thickness? Are they irregularly worn edge to edge?

Some folks do replace rotors at each pad change, most shops will at least resurface at each change (replacing them every other time or so when they can't be resurfaced anymore), but nobody does it because of exterior rust - which is pretty much normal. I imagine if your car has been sitting idle outdoors for 6 months, you may have a more serious rust issue - but that certainly doesn't sound like the case.

As with most preventative advice, you have to weigh the costs and benefits. If they're $20 rotors, it may be reasonable to go ahead. If they're $80 rotors, I'd probably think twice myself.

Either way, the "advice" of replacing rotors because of exterior rust would prompt me to replace the mechanic (assuming there's no other reason to replace them).

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This is a great question, so let me help. First, I am the owner an auto repair center in New Hampshire and rusted brake rotors are almost an everyday occurrence here. If you live in an area that uses a lot of salt on the roads in the winter, like we do, then this information most likely pertains to you. 99% of the rotors that we have to replace are due to rust on the inside braking surface, not the outside part that you can see. You would think that both sides of the rotor would rust equally but that is NOT the case. The rust you described on the edges of the rotor and the hub are normal and most of the times is harmless, but that is where it starts. There are aftermarket brake suppliers (Centric is one name that we use) that install a powder coating material on the edges and hub of their rotors to prevent the rust from starting and then working into the braking surface. Resurfacing brake rotors is not a common procedure here in New England for many reasons. First, the rotors made today are not like the "Old Days" where there was enough metal to resurface them a couple of times and still be within the factory thickness specification. Today's rotors are thinner from the start and in most cases will be under the discard thickness before the rust is totally removed. Also, the quality of the metal used in brake rotors is not all the same. A "Cheap" or "Economy" rotor is more likely to warp or rust quicker than a premium component simply due to how and what they are made with.

Since we are on the topic of "Rust" and "Brakes" there is another area that is greatly effected and that is the moving parts of the calipers and pads. When you step on your brake pedal hydraulic pressure pushes on a piston, or pistons, which forces the pads against the rotor. This is what creates the friction needed for stopping your car. When you release the pedal everything needs to relax on it's own in order to release your brakes. If rust builds up on the surface where your brake pads ride or on the pins the calipers slide on then your brakes could still be applied slightly and you'd never know it. This will cause premature and sometimes uneven wear to your brake pads. This will also create excessive heat build up in the rotors causing them to possibly warp giving you a pulsation feeling in your steering wheel or brake pedal.

With the influx of auto parts being manufactured overseas it is difficult to know exactly what is being installed on your car. This is where trusting your mechanic and service center is crucial and be sure to tell them your expectations of the car and the type of driving you regularly perform. Unfortunately, brakes is not an area that you should blindly look for the "Cheapest" quote because there is no telling what you could end up with. Hope this helps!

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Rust will usually be there to some extent. Rust on the edges does not affect anything. Rust on the surface would probably get ground off during braking if there is any.

Grooves in the rotors means you need to grind it flush or replace it.

Rotors rarely actually get warped. Usually brake deposits cause uneven surfaces. Many people get scammed into thinking their rotors are warped when it is fixable (It is even possible to do it with your brakes... but requires higher initial speeds and dangerous maneuvers. not recommended).

Just watch out for deep grooves and minimum thickness.


European style brakes - brake pads are usually made of much harder material (geared towards much higher speeds and smoother roads) and therefore cut into rotors much easier and recommend new rotors at least every 2 pad changes.

American style brakes - brake pads are usually made of softer material and the rotors last much longer. Recommend when the rotors are worn out... varies a lot due to materials and usage.

This information is from doing research for a friend about his German car and how the dealership recommends that he change rotors EVERY time he changes the pads. I forgot some of the numbers that go along with this but this is the gist of it.

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It's pretty obvious from reading all these replies, that the mechanic shops want you to always replace your rotors, and pay them to do it. Rust on the edges is normal and will happen with new rotors in less than a year, depending on where you live. If the rotors have never been resurfaced, you don't have any deep grooves, and your brakes aren't shuddering when you stop, then it's completely safe to install new pads. The worst that is likely to happen even with worn rotors, is the new pads wear unevenly and don't last. As for the mechanic that told you that rust around the edges indicated replacement, you need to replace the mechanic.

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You forgot about burnishing the rotors, then bedding the brake pads. This is very important if you want to get the best performance out of your braking system. While it may be "completely safe", it is not optimal. –  Paulster2 Jul 17 at 14:51
    
I agree Paulster, burnishing is a good idea and helps the pads bed faster, although with rotors that show little-to-no signs of wear, it's hard to tell the difference between burnished and unburnished. Besides, if you wanted to be 100% optimal, you should replace the rotors every time, no matter how little wear, as new rotors will always be better than used ones that are burnished. But that would be like saying that when your car has 50,000 miles, you have to replace it with a new one. –  k3nc Jul 18 at 22:24
    
A lot of people think that way (my wife being one). The only reason I suggest replacing them every time is the extra cost is minimal when compared to what it costs get them turned, then the extra time it takes to make it happen (taking them somewhere and waiting on them to do the job). People have to figure out what their time is worth. Personally, my two to three hours saved is worth the few extra dollars the new rotors will cost. I guess if you have a rotor lathe at home, doing it yourself would be a good option. –  Paulster2 Jul 18 at 23:02
    
Before you said not to forget burnishing the rotors and bedding the pads. Now you're saying you need to replace the rotors every time, otherwise you have to get them turned every time. However when there is no visible wear you don't need to do either. If there is significant scoring (making turning necessary) in my experience there is never enough rotor left to have them turned. So I would agree with you if there is visible wear to replace the rotors, if not then just replace the pads. That saves the most time and money. –  k3nc Jul 19 at 23:45
    
That's not what I said. I was commenting on your lack of wanting to change out the rotors. My preference is to change out the rotors every time. You don't absolutely have to change them out. It is your preference not to change out, burnish, or resurface the rotors. This wouldn't be my first choice. You can do it the way you suggest if you want a half-baked job. Personally, I like to be able to stop in the best distance possible. Not having a fresh surface on the rotor limits their effectiveness. It's hard to bed the new pads without one. –  Paulster2 Jul 20 at 1:02

The direct answer is that you have to replace your rotors when they start looking like this:

enter image description here

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I've seen rotor worse than this, Juann! It's pretty fantastic when people have their rotors worn down to the veins with no surface apparent whatsoever. Great stuff! –  Paulster2 Jul 18 at 23:04

Regarding rust on the rotors, I live in a humid part of the US on a steep hill. After a particularly wet spell and leaving the car parked for a couple of days, I can actually feel the rust on my rotors the first time I brake going down the hill. They feel "scratchy." That rust wears off after just a few stops, and you can see that they're shiny and smooth again. I once left my car parked for 6 months. The first time I drove it, the rear brake shoes rusted so bad they were stuck to the drums (I left the e-brake on all that time) and the car wouldn't move. I actually had to jack the car up and pull both drums in order to break them loose. Since the rust was not uniform, you could feel pulsating the first few times I braked. But soon the rust wore off and it braked normally again. Though I'm sure rust accelerates the wear, I'm still driving on those same drums and shoes, 30k miles later, and my brakes work perfectly.

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I have not change the rotors in my car since I bought it. My car has more 110,000 mi and it is 12 years old and every time a mechanic tells me I need to change rotors I tell them that I only want the pads, I follow the manufacturer specs and I have not any problems so far. I will be prepare to change the rotors in my next replacement of brake pads. When my car reaches 120,000 mi

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