# Brake Rotors **URL:** \ **Category:** Factual Questions\ **Created:** [March 30, 2012, 1:54pm UTC](https://boards.straightdope.com/t/brake-rotors/617272 "2012-03-30T13:54:46Z")\ **Posts on this page:** 16\ **Page:** 2
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [March 30, 2012, 5:54pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/21 "2012-03-30T17:54:11Z")
> [@jtgain](#): > > ..It is pitifully easy. .. I know, eh? You might need a clamp to compress the brake piston, but easy-peasy. ---
**Author:** ![SanDiegoTim](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@SanDiegoTim](https://boards.straightdope.com/u/SanDiegoTim)\ **Post date:** [March 30, 2012, 6:12pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/22 "2012-03-30T18:12:53Z")
Brake rotor rip-offs occur because 99.99% of car owners are not in a position (skill and/or tools) to determine whether there is enough material remaining on the rotor to make re-surfacing feasible. Couple of years ago an employee came to me asking me about an $800.00 quote from her dealer to replace pads and rotors. Advised it was a bit high. I then aked her about symptoms to which she replied “steering wheel shake when braking from freeway speed.” Being suspicious of the diagnosis, to say nothing of the price quote, I recommended a friend’s shop for a second opinion. $60.00 later the shake was gone. As noted earlier, and unless you are equipped to make your own evaluation, you just need a good mechanic you can trust. Lots of good ones out there, not so many you can trust. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [March 30, 2012, 6:23pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/23 "2012-03-30T18:23:20Z")
I replaced the pads on my last van two weeks before trading it in. The rotors needed replacing. My mechanic warned me it would shorten the life of the new pads. But they’d still be fine for a few thousand miles. More than enough for a van getting traded in. The brakes worked great with new pads. ---
**Author:** ![SanDiegoTim](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@SanDiegoTim](https://boards.straightdope.com/u/SanDiegoTim)\ **Post date:** [March 30, 2012, 6:35pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/24 "2012-03-30T18:35:17Z")
FYI, brake rotor warpage increased dramatically when the federal government prohibited asbestos from being used in brake pads. Asbestos was relatively efficient w/regard to the dissipation of heat. Heat not dissipated ends up in the rotor. Another source of warpage is indiscriminate use pneumatic impact wrenches which frequently over-torque lug nuts. A good shop will only use a torque wrench to tighten lugs. ---
**Author:** ![obbn](https://avatars.discourse-cdn.com/v4/letter/o/d6d6ee/32.png) [@obbn](https://boards.straightdope.com/u/obbn)\ **Post date:** [March 30, 2012, 6:37pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/25 "2012-03-30T18:37:11Z")
Try going to an indipendent mechanic for your brakes. I have never met one yet that didn’t measure the rotor and if it was in spec, to turn them. My local NAPA will still turn rotors for you if you are doing the job yourself. The reason the dealers don’t want to turn rotors are: it is easier to replace than turn, bigger profit in new parts than rehabing old ones and sadly, most OEM rotors are paper thin, making turning impossible more than once if even that. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [March 30, 2012, 7:45pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/26 "2012-03-30T19:45:55Z")
> [@Hail\_Ants](#): > > Also, I know it’s hard to accept but rotors should _always_ be cut when you replace the pads. They’re not cut merely to remove any grooves from pad rivets, they’re cut to ‘roughen’ up their surface after being polished perfectly smooth for thousands of miles. The brakes will work much better this way. One reason it’s hard to accept is because **CAR MANUFACTURERS** specifically instruct to **NOT** resurface rotors unless they’re warped or have significant scoring, e.g. greater than 0.060". Another is that an uncut used rotor surface works better than a new or resurfaced one, until the fresh surface has been embedded with some pad material. Decades ago we routinely resurfaced or replaced rotors to get the desired surface finish for the purpose of minimizing noise. With modern noise-reduction pads, this is usually no longer an issue. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [March 30, 2012, 7:59pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/27 "2012-03-30T19:59:18Z")
> [@dauerbach](#): > > 200 Pontiac vibe with 225,000 miles. > > The brakes are making a grinding sound. I am assuming they need to be replaced. When I take them in they will probably say I need to have the rotors replaced (they never seem to be able to turn them these days). If I tell them to just replace the pads (in deference to the miles on this car) does anything bad happen. Is this a safety issue, or an aesthetic one? Grinding sound usually means a pad has worn totally and its metal backing is digging into the rotor. A certain amount of resultant rotor wear is acceptable for reuse as-is; beyond that amount typically means there’s not enough metal to resurface and reuse and thus new rotors are called for. Where to draw the line between safe and unsafe can come down to a matter of professional opinion, and will vary with one’s personal experience, regard for manufacturer’s specs, and “worry factor” about safety-related issues. > [@dauerbach](#): > > Fortunately, I have a mechanic that I trust. Let’s say he thinks the brakes will continue to grind because the rotors are slightly scored, and that the brake pads will then wear out more quickly. He will honestly recommend turning or replacing. My thought is that I can live with the noise, and the pads will still probably outlive the car (I drive a lot but most is limited access roads and I don’t brake that often). If you trust him, then just tell him what your goal is. With new pads, noise isn’t likely, it’s braking power and longevity that are the concerns. But this fellow will have a **HUGE** advantage over us here in actually seeing the rotors. > [@dauerbach](#): > > It happened quite suddenly. I was away for a week and when I got back and drove the car for the first time it initially felt like the breaks were on, then I heard a quiet “pop” and then when I used the brakes I heard the grinding sound. This I find worrisome. It may be part of normal wear patterns, or it may be something more sinister – and serious – like a pad falling out place. Best bet: have it checked yesterday. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [March 30, 2012, 8:06pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/28 "2012-03-30T20:06:11Z")
To clarify post #26, factory instructions are to reuse rotors as-is, without resurfacing, _unless_ they have certain specified problems. ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [March 31, 2012, 2:07am UTC](https://boards.straightdope.com/t/brake-rotors/617272/29 "2012-03-31T02:07:02Z")
Often the outer edge of a rotor has a ridge outside where the pads rubbed. It needs to go. I simply grind it off. ---
**Author:** ![Terry\_Kennedy](https://avatars.discourse-cdn.com/v4/letter/t/c57346/32.png) [@Terry\_Kennedy](https://boards.straightdope.com/u/Terry_Kennedy)\ **Post date:** [March 31, 2012, 3:19am UTC](https://boards.straightdope.com/t/brake-rotors/617272/30 "2012-03-31T03:19:25Z")
> [@dauerbach](#): > > It happened quite suddenly. I was away for a week and when I got back and drove the car for the first time it initially felt like the breaks were on, then I heard a quiet “pop” and then when I used the brakes I heard the grinding sound. While you should definitely have things inspected by someone who knows what they’re doing (shop or amateur), this can occasionally be innocuous. Rust can build up on the surfaces of the rotors. Most often, this is from something like washing the car and spraying water on the rotors, then letting the car sit where it is, provding no chance to disperse the water. It can also happen from road salt being splashed onto a parked car. In some cases, this can be so extreme that the car will act like it is “stuck to the floor” and will refuse to move until the brakes are freed up. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [March 31, 2012, 4:38am UTC](https://boards.straightdope.com/t/brake-rotors/617272/31 "2012-03-31T04:38:28Z")
I hadn’t thought of what what **Terry Kennedy** mentioned – surface rust (usually invisible) can cause pads to stick to the rotor, and can cause (harmless) noise that sounds for all the world like metal grinding away vigorously. Usually it will get cleaned off of the rotors in a few stops. How much has the car been driven since the noise came on? ---
**Author:** ![dauerbach](https://avatars.discourse-cdn.com/v4/letter/d/c2a13f/32.png) [@dauerbach](https://boards.straightdope.com/u/dauerbach)\ **Post date:** [March 31, 2012, 12:47pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/32 "2012-03-31T12:47:29Z")
I would say the brakes have been used moderately in the time since this has occured. All four rotors have rust on their surface. Hopefully this is all it is. It is going in on Monday, mainly to get the check engine light turned off (I have a mandatory emissions inspection coming up). It love this car, it has been very good to me. I just hate to spend much money on it when it has so very many miles. ---
**Author:** ![Woodenspoon](https://avatars.discourse-cdn.com/v4/letter/w/bc79bd/32.png) [@Woodenspoon](https://boards.straightdope.com/u/Woodenspoon)\ **Post date:** [March 31, 2012, 2:39pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/33 "2012-03-31T14:39:22Z")
Take off the wheel and simply measure the rotor, look up the acceptable wear limit. If it squeals as well as grinds then its the pad wear indicator…do not ignore that. Videos of how to change the pads is easy to find on youtube, as a car fix job its pretty simple for most cars, and cheap to boot, a simple cheapo c clamp is enough to push the piston back in so yu can reinstall the thing. i did mine after watching a few youtube videos and reading the chiltons/haynes manual. but first things first, take the wheel off and look at the rotor. rotor wear depends on the type of pad, the harder ceramics and such will go through your rotor faster. factory pads and cheaper pads won’t. there shouldn’t be rust on the rotor surface, any should be worn away just from brake use. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [March 31, 2012, 3:00pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/34 "2012-03-31T15:00:11Z")
> [@Woodenspoon](#): > > Take off the wheel and simply measure the rotor, look up the acceptable wear limit. Step one is “acquire a [micrometer.](http://en.wikipedia.org/wiki/Micrometer)” > [@](#): > > there shouldn’t be rust on the rotor surface, any should be worn away just from brake use. yeah, that’s true; if there’s rust on the braking surfaces even after driving, then the caliper is likely stuck on its slide. ---
**Author:** ![Woodenspoon](https://avatars.discourse-cdn.com/v4/letter/w/bc79bd/32.png) [@Woodenspoon](https://boards.straightdope.com/u/Woodenspoon)\ **Post date:** [March 31, 2012, 11:47pm UTC](https://boards.straightdope.com/t/brake-rotors/617272/35 "2012-03-31T23:47:28Z")
micrometers on ebay are next to nothing in cost;) ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [April 1, 2012, 2:49am UTC](https://boards.straightdope.com/t/brake-rotors/617272/36 "2012-04-01T02:49:25Z")
If discard is 1.0 inches, a good scale will tell what you need. Whether it is 1.002’’ or 0.998 makes little difference. [Previous page](https://boards.straightdope.com/t/brake-rotors/617272.md?page=1)