If you replace pads before they’re down to metal, and the rotors look perfect, why bother machining them?
They can look fine to the eye, but be warped.
If you were not getting pulsing with the old pads you might be OK with out machining. I have done that several times. Might want to hit them with some sand paper to break up any glaze that might have formed. Clean them with brake cleaner/solvent afterwards.
The rotors on today’s vehicles are so thin, that by the time you go through a set of brake pads they’re worn to a point where they can’t be machined. So you run the risk of the rotors warping shortly after performing the pad replacement.
And even if the rotors don’t warp, there’s the chance that the brakes can make noise after the pad replacement because of improper friction material transfer. (look it up).
If you’re working on your own vehicle? Sure! You can just do a pad swap and cross your fingers. Then if the rotors warp or the brakes make noise then you fix it on your dime.
But when somebody is paying you for a brake job, you make sure the job is done right the first time.
Tester
IMHP rotors due to minimal standards should be replaced with brake pads. If they have enough metal to be resurficed go for it, though I know enough people that get by with just replacing pads, but not how I would do it.
Yeah, you don’t want to turn down a rotor anymore. Plus I think you will find the performance superior after replacing both rotors and pads. I just do it now as a matter of course. Of course I’m not driving 50,000 miles a year now so in the past I’d tend to make parts stretch a little, but you’ll get a lot more improved braking with new rotors.
As long as the rotors aren’t surface glazed, and meet the run-out and thickness specs, I don’t re-machine my Corolla’s rotors as standard practice when replacing the pads. I do dress the surface a bit with some 120 to 160 grit sandpaper, making a sort of cross-hatch pattern.
On my Camry I had some front pad left but just changed them because they had 90K miles and I had already bought the pads!! Anyway, around 10K miles later the rotors were warped and I had to change everything again. Now I do my own work and for me the cost was $15 plus my time, but if a shop did this it would be considered poor service.
I never have my brake rotors machined anymore. If they are warped…I buy new replacements.
Totally agree with folks, if you are being paid…just replace the rotors. If it is a diy, slapping pads on is just fine. Some rotors can last 200K miles, so why replace them too early. Lots of folks don’t care about a slight pulsing, if any at all.
If they’re yours, and your car is stopping straight and smooth, put on some pads and go.
But shops have very legit reasons for insisting on replacing the rotors… it greatly reduces the chances of a dissatisfied customer. Emphasis on the word “greatly”. And it doesn’t add that much to the cost of the job.
You can’t eyeball warpage or parallelism issues is why.
If I was running a brake shop, I would insist on replacing the rotors every time, the liability is not worth the risk.
When I do my own, I measure the thickness of the rotors and compare it to the min and new dimensions. If they are less than half worn, then I just put on new pads. I don’t deglaze the rotors either, its just a waste of time.
After replacing the pads, the new pads will sometimes cause a build up of residues on the rotor (new or old) that will cause a pulsing feeling in the brake pedal. It is not warped rotors as many believe and the cure is simple, do a couple of hard braking stops from about 60 mph to heat up the rotors and burn off the residues from the new pads. It works, its cheap. However if you use cheap pads, you may have to do this every couple thousand miles for awhile.
If the steering wheel shakes violently while under light braking, then you may have warped rotors and they should be replaced.
I will never have rotors turned. If the rotors aren’t scored and the car stops without pulsating in the pedal, then it’s just pads that are replaced. If the rotors are scored, the rotors are replaced. If a shop suggests turning the rotors, I take the job elsewhere.
Just to reiterate, in my experience, you’ll get 20-30% better braking performance by replacing the rotors, even if they are not warped or damaged. So even though as a DIY you can get by fine without replacing the rotors, you will get better braking and satisfaction by replacing them. The only problem is you have to pull the calipers and bracket to replace them so it adds to the time and effort, but your time is free anyway.
I will never have rotors turned. If the rotors aren’t scored and the car stops without pulsating in the pedal, then it’s just pads that are replaced. If the rotors are scored, the rotors are replaced. If a shop suggests turning the rotors, I take the job elsewhere.
There’s a lot more to the surface of a rotor than just scoring. Variation of thickness from the center hub to the outer diameter is common. Just because you don’t feel a pulsation doesn’t mean the rotors are true. Blue or hot spots are common for stop and go traffic. And just replacing pads onto a glazed surface can result in squeaking brakes.
We resurface rotors and drums as part of every brake job. If the rotors are at minimum thickness or turning them will put them at minimum, we replace them.
I have to guarantee my work. I can’t afford to just slap pads on. But for the guy working on his own car in the driveway, sure, give it a try.
I mostly agree with asemaster except for the part of replacing pads to a glazed surface causing squeaks. I have done that many times and I have never had squeaky brakes, never.
It’s well known in industry that machining leaves residual stresses in the metal, and if extreme accuracy is critical the metal has to be “stress relieved”, an oven process that relaxes the structure of the metal. Having spent so many years in industry, I bring with me these assumptions. Knowing that, I don’t bother machining rotors. Since I can no longer physically do the work, I always tell the person doing it not to machine the rotors… just replace them.
I’ve also wondered if machining vented rotors leaves uneven metal on each side of the rotor (each side of the vent fins) and thus an uneven ability to tolerate heat, leading to warping once again. I have zero actual data to back that, but I just wonder of it’s true.
I’m a fleet mechanic
We machine rotors and drums, as needed. In fact, we are strongly discouraged from replacing rotors, unless they are below discard thickness.
However, when I’m fairly certain that rotors are warped . . . because the brake pedal was kicking during the test drive, for example . . . I measure runout at all corners, and measure rotor thickness. I do a quick calculation, to determine if a rotor will “survive the cut or not.” Sometimes, it’s obvious that I need to order rotors, right off the bat
Another thing to consider . . . we have brake pads in stock for most of our common vehicles. If I can successfully cut rotors, install new pads, and get the truck out the same day, that’s pretty efficient, by my standards. We do not stock rotors, because we go through many pads, versus a few rotors here and there
I also machine my own personal rotors. I put my car on jackstands at home, remove the rotors and throw them in the trunk of the spare car. Then I drive to work, in the spare car, and machine my rotors during my lunch break. When I get home, I install the rotors, along with factory brake pads. Haven’t regretted it yet
I had a 1978 Oldsmobile Cutlass and a brake shop installed pads but said the rotors were fine. The brakes worked well. I happened to mention that I also had a 1988_Taurus. The mechanic thought I ought to have him check the pads after I told him how many miles were on the car. He told me that these Taurus models had thin rotors and shouldn’t be turned. ,Two weeks after I had new pads on the Taurus, I had a recall notice from Ford for the rotors. I got new rotors at no charge. Since that time, I have told the shop not to turn the rotors. If necessary, just replace them.
There is nothing wrong at all with machining rotors as long as the job is done properly. That means no going below the minimum thickness, cleaning the rotor after machining, and not doing as some have been known to do; making the last cut at warp speed instead of using slow cut.
Most rotors have about .030 of an inch to play with before discarding. Some, like my Lincoln, have double that.