# changing brake pads without turning rotors **URL:** \ **Category:** Factual Questions\ **Created:** [September 8, 2014, 4:29am UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828 "2014-09-08T04:29:17Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [September 9, 2014, 2:18pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/21 "2014-09-09T14:18:01Z")
> [@Hail\_Ants](#): > > I grew up working on cars, but didn’t make it my trade (got into IT instead). Still, I’ve known and know car repair people and when doing a brake job it was/is considered SOP to \*always \*cut the rotors/drums regardless of their condition. Cutting them didn’t make it the ‘deluxe’ brake job, not cutting them made it the amateurish, shittier one. The fact that the rotors/drums are perfectly smooth is the reason you get them cut. They’ve been polished so smooth that the pads/shoes don’t ‘grab’ as well. If they were in good condition you might just do a fine cut (usually you did a rough & a fine cut) but the point is to make the surface microscopically less smooth so the pads grip better. > > We would often do them without cutting the drums/rotors, we called it a ‘pad slap’, but only to our own cars if we were broke or a friend’s who was a cheapskate. > > And good luck trying to find drums/rotors (or most any car parts) that aren’t made in China. You’d have to go to the parts dept at a new car dealership and you’ll literally pay five times the price (and they still might be Chinese). And Chinese car parts are generally not badly made. They’re inexpensive because their labor costs are about one 1/100 of ours. ``` You are very wrong here on all counts, if your rotors are smooth and flat the better method and safer method is to leave them alone. Myself and several others here have been lifetime proffessional mechanics. Amatuers are the ones who think you always have to turn them. ``` ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [September 9, 2014, 3:13pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/22 "2014-09-09T15:13:49Z")
Whatever. Maybe it was all a scam perpetrated by the industrial-brake-rotor-complex. 😃 But it kind of makes sense to me that rotors & drums that are polished mirror smooth are not going to work as well as ones that have a slight cut roughness. And since the metal is harder than the pad material the pads will wear sooner than the rotors will get polished smooth again. Or words to that effect… ---
**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:** [September 9, 2014, 3:52pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/23 "2014-09-09T15:52:34Z")
> [@Steven\_G](#): > > **Warped disks - no such thing or at least VERY rare** > > [http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths](http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths) > > [http://www.mossmotors.com/SiteGraphics/Pages/brake\_discs.html](http://www.mossmotors.com/SiteGraphics/Pages/brake_discs.html) As my high school U.S. history teacher would say, so what? (Not as snark, but to stimulate thinking about the significance of the matter.) Whether there’s warpage or thickness variation, the result is pedal pulsation and the fix is to turn or replace the rotors. It is interesting that the conventional wisdom may be incorrect, but it doesn’t matter in the real world. A properly done brake job includes test driving in such a way as to help break in the new pads. ---
**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:** [September 9, 2014, 4:05pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/24 "2014-09-09T16:05:14Z")
> [@Hail\_Ants](#): > > …I’ve known and know car repair people and when doing a brake job it was/is considered SOP to \*always \*cut the rotors/drums regardless of their condition. Cutting them didn’t make it the ‘deluxe’ brake job, not cutting them made it the amateurish, shittier one. This was indeed SOP in the 70’s and 80’s (see post #5). Disc brakes have an inherent tendency to make annoyance noises (usually squealing), and back then a lot of research was being done towards eliminating that. Turning rotors to get the right surface finish and lubricating all metal-to-metal contact points were the key elements for minimizing the chance of noise. Things started to change in the 90’s with the development of new brake lining formulations, and nowadays the regimen of “always turning” is obsolete (lubricating contact points is not). The official instructions from vehicle manufacturers say to use the rotors as is unless there’s a specific problem (see post #14). ---
**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:** [September 9, 2014, 4:11pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/25 "2014-09-09T16:11:23Z")
> [@lazybratsche](#): > > If I may continue this hijack, can anyone recommend a brand or manufacturer of brake rotors? I have been impressed with Bosch QuietCast rotors. They’re somewhat pricy (though not ridiculously so), but I’ve found their quality to be superb. ---
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [September 9, 2014, 10:18pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/26 "2014-09-09T22:18:06Z")
> [@lazybratsche](#): > > If I may continue this hijack, can anyone recommend a brand or manufacturer of brake rotors? The Whatever Autozone Sold Me front rotors I installed about 20,000 miles ago on a Mazda3 are already showing signs of heavy wear, with substantial grooves and pulsing that’s starting to get serious. I have had [ATE One](http://www.tirerack.com/brakes/brakes.jsp?make=ATE&model=PremiumOne+Slotted+Rotor) rotors on my Subie for three years now and have been very happy with them. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [September 9, 2014, 10:51pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/27 "2014-09-09T22:51:29Z")
> [@Gary\_T](#): > > I have been impressed with Bosch QuietCast rotors. They’re somewhat pricy (though not ridiculously so), but I’ve found their quality to be superb. Should calipers be bled when the piston is forced back to avoid flushing contaminates into the lines? Premise the answer on cars with anti-lock brake systems. ---
**Author:** ![Morgenstern](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@Morgenstern](https://boards.straightdope.com/u/Morgenstern)\ **Post date:** [September 9, 2014, 10:58pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/28 "2014-09-09T22:58:18Z")
> [@Gary\_T](#): > > Absolutely acceptable and actually even recommended to leave the rotors be if they don’t show problems (gouges, too thin, warped). There should be no need for bleeding. > > … However, it’s best to have the rotors looked at by a pro for signs of thermal damage. And don’t let the calipers dangle at the end of the brake line when changing the pads. That could cause problems. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [September 9, 2014, 11:53pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/29 "2014-09-09T23:53:38Z")
> [@Magiver](#): > > Should calipers be bled when the piston is forced back to avoid flushing contaminates into the lines? Premise the answer on cars with anti-lock brake systems. That’s the way I do it and I’ve never bled the brakes. That’s the whole point of doing it that way, so you don’t have to bleed the brakes. If you are going to bleed them anyway, might as well open the lines so that it’s much easier to push the piston back. I have a special tool to push the piston back, so it’s not like I’m just forcing it with a screwdriver or a pry bar. I’ve never had a problem on cars with or without antilock brakes. If there’s an issue with doing it this way I’d like to know what it is. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [September 10, 2014, 12:29am UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/30 "2014-09-10T00:29:31Z")
> [@engineer\_comp\_geek](#): > > That’s the way I do it and I’ve never bled the brakes. That’s the whole point of doing it that way, so you don’t have to bleed the brakes. If you are going to bleed them anyway, might as well open the lines so that it’s much easier to push the piston back. > > I have a special tool to push the piston back, so it’s not like I’m just forcing it with a screwdriver or a pry bar. I’ve never had a problem on cars with or without antilock brakes. If there’s an issue with doing it this way I’d like to know what it is. I want to say I saw it on Motorweek but I’m not sure. Something about not forcing the piston back without opening up the bleed valve because it would force contaminants back into the anti-lock brake system. Sounded like overkill to me but I did it on my last brake change because the car had antilock brakes. ---
**Author:** ![RivkahChaya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rivkahchaya/32/8919_2.png) [@RivkahChaya](https://boards.straightdope.com/u/RivkahChaya)\ **Post date:** [September 10, 2014, 12:56am UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/31 "2014-09-10T00:56:23Z")
> [@JerrySTL](#): > > I’ve had issues with the cheaper Chinese rotors warping. And I do tighten the lug nuts with a torque wrench using a ‘star’ pattern. > > As the OP asked, sometimes I don’t bother to turn the rotors if they are smooth. > > If the rotors aren’t very smooth, then I’ll have them turned. > > If they can no longer be turned, I’ll go with the more expensive rotors with the hope that they are worth the extra cost. > > Brakes and tires are two places where it doesn’t pay to be cheap (unless you are selling off the vehicle shortly). > [@HoneyBadgerDC](#): > > You are very wrong here on all counts, if your rotors are smooth and flat the better method and safer method is to leave them alone. Myself and several others here have been lifetime proffessional mechanics. Amatuers are the ones who think you always have to turn them. > [@Gary\_T](#): > > This was indeed SOP in the 70’s and 80’s (see post #5). Disc brakes have an inherent tendency to make annoyance noises (usually squealing), and back then a lot of research was being done towards eliminating that. Turning rotors to get the right surface finish and lubricating all metal-to-metal contact points were the key elements for minimizing the chance of noise. Things started to change in the 90’s with the development of new brake lining formulations, and nowadays the regimen of “always turning” is obsolete (lubricating contact points is not). The official instructions from vehicle manufacturers say to use the rotors as is unless there’s a specific problem (see post #14). I worked in a shop in the mid-90s, and I also worked in a National Guard motor pool. In both places, we inspected rotors for warp visually and with micrometers (and with a test drive, or noting a customer complaint about squealing or pulsing) to evaluate for the need to turn. We were happy to give customers the news that we didn’t have to turn or replace rotors, because it meant they were more likely to do the work there and then. It took less time to do just pads, so we got more cars through if we did shorter jobs, and there was very little mark-up on things like rotors, so it didn’t matter that much to us whether we did them or not, except to the extent that we wanted to do the job right, and get repeat business. Sometimes, a person would complain that they had pulsing after rotating their own tires, or putting on the spare, or something. We would take the lug nuts off, and replace them to spec with the torque wrench. Pulsing gone. So, sometimes the rotor is being warped by improperly tightened lug nuts, but if it hasn’t been running that way for a long time, it will straighten back out. It’s always worth a try. ETA: If the wheel was missing its balance weights, we’d check the balance before replacing it. That sometimes was a cause of pulsing as well. ---
**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:** [September 10, 2014, 7:42am UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/32 "2014-09-10T07:42:44Z")
> [@Magiver](#): > > Should calipers be bled when the piston is forced back to avoid flushing contaminates into the lines? Premise the answer on cars with anti-lock brake systems. I’ve heard for years that yes, the bleed screws should be opened so that whatever debris might be in the brake fluid goes out the bleed screw rather than back up into the lines. The fear is that some tiny wayward piece of crud might jam up a port or valve in the ABS control unit, requiring it to be replaced for big – sometimes BIG – bucks. Nevertheless, I’ve never heard of this problem actually happening. I think it falls into the category of “Well, maybe we don’t really need to take this precaution but hey, it’s better to be safe than sorry.” ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [September 10, 2014, 10:45pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/33 "2014-09-10T22:45:59Z")
> [@Gary\_T](#): > > I’ve heard for years that yes, the bleed screws should be opened so that whatever debris might be in the brake fluid goes out the bleed screw rather than back up into the lines. The fear is that some tiny wayward piece of crud might jam up a port or valve in the ABS control unit, requiring it to be replaced for big – sometimes BIG – bucks. Nevertheless, I’ve never heard of this problem actually happening. I think it falls into the category of “Well, maybe we don’t really need to take this precaution but hey, it’s better to be safe than sorry.” That’s how I felt when I heard it but did it anyway. Of course I broke one of the bleeder valves off and had to replace a caliper. Always in too big a hurry to squirt a little something on it first. While I’m thinking of it, what’s the best thing to spray on rusty corroded stuff? ---
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [September 10, 2014, 11:12pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/34 "2014-09-10T23:12:05Z")
[quote=“Magiver, post:33, topic:697828”] That’s how I felt when I heard it but did it anyway. Of course I broke one of the bleeder valves off and had to replace a caliper. Always in too big a hurry to squirt a little something on it first. If you want the answer to “what’s the best thing to spray on rusty corroded stuff” perhaps you should open your own tread in another forum. IMHO comes to mind. I would also like to know what results you are trying for. Do you just want to be able to unbolt items, or do you want the metal to be “rejuvenated” to like new condition? BTW, as far as the OP is concerned, I agree with Gary T and others. I only turn the rotors +/or drums when they are warped or when they have grooves worn in them. I do replace them if they are “out of service limits” IRT thickness, diameter, +/or warp-age. ---
**Author:** ![Alex\_from\_CB](https://avatars.discourse-cdn.com/v4/letter/a/278dde/32.png) [@Alex\_from\_CB](https://boards.straightdope.com/u/Alex_from_CB)\ **Post date:** [September 12, 2014, 1:52pm UTC](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828/35 "2014-09-12T13:52:21Z")
Just changed rear brakes, rotors on my flawless, pristine '98 Acura RL that has 163,000 miles. I’ve owned this car for 11 years and do much of the maintenance myself. I had the fronts done a few years ago by a mobile mechanic who comes to my house. Used Advance Auto Wearever rotors and Wagner ThermoQuiet Ceramic Pads previously on the fronts. They’ve be prefect. Used the same on the new rear brakes I installed last month. The regular price for the 2 rotors was $55.18. Pads, regular price was $55.99. With the discount code always available on their website I paid… net, net $76.33. My Mechanic charges $35 per hour. He finished in about 50 minutes including a road test. I paid him $40. Total cost…$116.33. Brakes are smooth as silk. Stop on a dime without any pull and with very little, light colored brake dust. I will use no other pads and wouldn’t think of ever turning a rotor again when a new rotor can be had so cheaply. [Previous page](https://boards.straightdope.com/t/changing-brake-pads-without-turning-rotors/697828.md?page=1)