I have heard it is proper practice to replace or resurface your brake rotors every time your do a brake pad replacement. Does this need to be done every single time or is it overkill? Maybe it is just something easy to do, might as well replace while you are in there type of thing?
The decision to replace is largely based on the thickness. The repair manual should tell you the minimum thickness, below which you should replace the rotors when doing the repair. Use a pair of calipers and measure the rotor thickness, if you're below this number you need to replace the rotors.
You may also wish to replace the rotors if you have particularly heavy use planned and you are getting close to the limit. For example, if you live in the mountains, do a lot of towing, are planning to attend track days...
You definitely need to get them resurfaced if they are warped or damaged. Usually you can feel if they are warped through the brake pedal when stopping -- instead of a smooth stop it will kind of vibrate or pulsate when braking at higher speeds. It's very noticeable. This can be measured with a dial gauge and checked against the repair manual's recommendations for "runout". You will need a dial gauge, and some sort of a mount to hold the gauge steady while you spin the rotor.
Damage is usually caused by the old brake pads wearing completely through and tend to leave a very rough surface on the disc. These should definitely be turned, if possible.
Before having a damaged or warped set of rotors turned, check their thickness. If they're close to the minimum, resurfacing them will leave you with rotors that are too thin.
If you're at this point, you should have rotors that are thick enough and not damaged. Many people recommend resurfacing of them so the pads and rotors can better mate and wear into each-other. I tend to agree with this, but I have replaced pads on cars that I drive less spiritedly without resurfacing them, and have not had problems.
There are three cases that cause brake rotors to need to be resurfaced/turned and/or replaced.
- Gouging of the rotor by the brake pad holding mechanism (the pad were rubbed completely away and the metal holding the pad start digging into the rotor)
- Warping of the rotor from extreme use (rotor gets too hot and warps upon cooling)
- The rotor itself wears down to a point that it is too thin and could possibly break when used (this generally occurs when brake pads made of a material that is harder than the rotor material and the rotor wears down instead of the brake pad)
Many mechanics recommend turning/resurfacing/replacing rotors everytime because there is more money to be made that way.
Wow, I'm in the minority here. It is my firm belief that you should have your rotors turned with every brake pad/shoe replacement! If you do not do this everything will work perfectly fine, until you apply the brakes then if your brake rotors/drums were glazed, heavily scored or worn out of parallel to the new brake pad your will stopping distance WILL be INCREASED maybe even up to several feet at highway speed. My local Napa store charges $10 to cut a rotor and will do it while you wait. Brake warping, is a misnomer, brake rotors generally do not warp. The pulsating condition felt through the brake pedal is actually pad material burned onto the rotor in one spot. This occurs after a very heavy braking incident which overheats the rotor then the application of the brakes in one spot on the rotor immediately following the incident. This is why the condition gradually goes away on its own. If you think about it a "warped" rotor would give no pedal feel as the caliper is free to move side to side for that very reason, where a thickening of the rotor in one spot on both sides generates a pulsing effect.
I don't believe in turning rotors anymore. If they're too thin, replace. Warped, replace (probably warped from heat, and if you warped them before, they're going to warp even faster as they get thinner). Grooves, as long as they're not deep, the pads and rotor will come to agree with each other pretty quick. Deep grooves, replace the rotor.
Along with the already mentioned and more common reasons of Gouges, Warped or being too thin there is another reason for getting them turned/resurfaced.
When using some higher quality brake pads, they will tell you if you are changing from one pad compound to another (either changing brands or product lines) to use new or re-surfaced rotors.
This comes into play most often for brakes being used on sports cars for track events and such.
I tend to drive my Subarus pretty hard, both on and off track, and I go through brake pads at around 15-20 thousand miles. My old Impreza is at 130,000 miles now and the rotors are absolutely fine - looking at the wear I'll get to 200,000 before they need a change.
If they are damaged/scuffed or have worn right down, obviously change them. Other than that, leave them be.
As a mechanic for over 35 years, I strongly recommend resurfacing even if the rotors look fine. It's a matter of cost. If they are the "slip over hub" type, new rotors are relatively cheap (like $28 each). With that said, peace of mind for under $100 is well worth it. New pads are ceramic and much tougher than metallic to "break in".
There is generally a minimum thickness marked on the disc by the manufacturer which marks the 'safe' limit at which you don't really want to risk exceeding.
I've changed my pads twice now on my current vehicle, and each time taken the discs off and individually checked them for signs of gouging, cracking and of course if it's passed the minimum thickness marker. You can measure the actual thickness of your disks using a micrometer. These can be picked up for fairly cheap from most car stores.
I've personally never seen the need to resurface the disk, a brand new brake pad will generally sit in the groove quite happil
No, what you need to do is check for the worn rotor warning signs after you change your brake pads. When you do a brake pad change, you can check the rotor for any visible damage then. If you want to know what constitutes a warn rotor, then you should read this article... http://www.cquence.net/blog/changing_brake_rotors/
Remember that some vehicle do not have their rotors turned at all. At BMW, a brake change meant new pads, new sensor, and a rotor check. The outcome of the rotors thickness meant either keep or replace, but never turn. There are other manufactures out there that have similar rotors/pad systems, so be aware of this.
I change the rotors and pads at the same time. I like the knowledge that my brake parts have the same service life. I live in a harsh climate that takes a toll on all parts that are close to the ground (snow, ice, salt, sand, rain and Lord knows what) attacking them. Safety is always worth a few extra bucks.
I replaced my brakes with assistance from my father-in-law to be able to do it myself, and avoid being needlessly gouged by mechanic shops. He was of the mind set that under most circumstances it's unnecessary to have the rotors resurfaced when changing brakes. What he had me do instead was to take some fine-grit sand paper (I used 600), and sand the rotor perpendicularly to the grooves, on both sides, in order help seat the pads better. It's been a few months and everything seems fine with the work I did.
They only need to be resurfaced if your car shimmies when braking.
If there are deep grooves in the rotors but it doesn't shimmy while braking, then you should machine them but you don't have to. Basically, the deeper the grooves the less surface area there is for the pads to grab onto. So you'll have a loss of breaking power but you probably won't notice it.