A brake rotor is basically a machined disk of a specific kind of cast iron. The rotor is sandwiched between the wheel and the hub and spins with the wheel.
A brake caliper clamps two pads of brake material against it, which creates friction and therefore stops the force.
Turning a rotor and resurfacing a rotor are the same thing. There are two ways to resurface a brake rotor once the caliper assemblies are out of the way.
In the first, each rotor is removed from the vehicle and placed on a brake lathe, which then shaves metal from the inner and outer surfaces to create clean, perfectly true, and parallel surfaces for the brake pads to bed into.
In the second, an on-the-car lathe is bolted onto the hub with the rotor in place, and the rotor is resurfaced in position. The advantage of that is that it takes into account the hub run-out or the out-of-trueness of the surface that the rotor mounts to.
Either way, the job takes a little more than an hour most of the time. Any shop that does brake service should have a brake lathe. Many auto parts stores have brake lathes. Any machine shop would probably have a brake lathe. On-the-car brake lathes are more common at dealerships, but many brake shops have them as well.
Pro-tip: There’s no way to know if a rotor needs replaced or not without measuring it and comparing that to the specs. There’s no way to know if a rotor can be resurfaced or not without measuring it and comparing that to the specs. When getting a brake inspection, asking for the measurements is a good idea. It gives you information you can use and assures you that the shop did the inspection correctly.
Cost of Brake Rotor Resurfacing
The operation of turning brake rotors is fairly similar to the operation of doing a brake job—the brake calipers and pads are removed. Then, the brake caliper bracket, followed by the rotor which is then resurfaced.
The labor time for rotor resurfacing is also the same as for a brake job—usually a flat 2 hours. So, at a shop with a $100/hour labor rate, the cost would be $200. At a shop with a $150/hour labor rate, the resurfacing rotors cost would be $300.
In other cases, the job might not be based on book time, as brake work often takes much less time than is called for, especially for an experienced technician. Many shops use a flat rate for various types of brake work. For resurfacing rotors, that can range from about $120 to $180 for a set.
Shops that do this are also more likely to have a lower flat rate for replacing rotors as an alternative to resurfacing.
Another case is when a rotor has already been removed from the vehicle for other work or whatever reason. Most auto repair shops, parts stores (if equipped), and machine shops will turn a loose rotor. The cost to turn rotors in this instance is about $15 to $25, as long as it has enough machinable material.
Why Do You Need to Turn Brake Rotors?
There are two reasons to turn a brake rotor. The first is to provide a smooth and fresh surface for brake pads to bed into and operate upon.
Brake rotors are typically resurfaced any time a new set of brake pads is installed, after which there is a short process of “bedding in”. This sometimes involves heat cycling that gives an operational cure to the pads themselves.
In the case of ceramic pads, it transfers a certain amount of friction material into the rotor. In the event that this doesn’t go well (for whatever reason), sometimes, noise arises. A cure for that is sometimes to resurface the rotors and repeat the bedding in the process.
The second purpose of rotor turning is to provide two ideally flat, true, and parallel surfaces. Wear and heat can result in some unevenness and run-out. If the surfaces of the rotor that the brake pads bear against aren’t perfectly true and parallel to each other, the brake pads will apply stopping force unevenly as the disk rotates, resulting in a feeling of brake pulsation.
Resurfacing Rotors Versus Replacing
When replacing brake pads, resurfacing rotors is recommended if the machining will leave enough thickness in the rotors for them to still be above their minimum wear limit when the pads are worn out. Every manufacturer provides a specification for the minimum rotor thickness, which is usually stamped or cast into the rotor itself.
On many modern vehicles, there isn’t a lot of leeway, though it varies from vehicle to vehicle. As a general rule, a rotor with less than 100,000 miles of ordinary driving on it might be fine to resurface, while a rotor with more mileage than that or one that has seen heavy use may be too close to the minimum thickness to machine. It all comes down to the measurement. If the rotors can safely be resurfaced, then the next question is cost.
It takes more time to turn rotors than it does to simply replace them, so there are cases where it is cheaper to replace rotors than to resurface them. On a 2012 Dodge Grand Caravan, for instance, even mid-range rotors can cost about $25 each, which can make the job about the same in cost to replace rather than resurface.
And one advantage is that a new rotor typically comes with at least a 12-month warranty against problems. It’s best to inquire and get an estimate of both ways to solve a rotor problem in advance.
What Else Can Go Wrong
Bedding-in Problems. Brake pads need to be “bedded in”, which means the surfaces of the pads and rotors transfer some material and mate well with each other. That happens best with a good, flat brake pad surface and a fresh rotor surface. Poor bedding in can cause glazed rotors and pads, squeaking or grinding sounds, and sometimes a shuddering on brake application. If that happens after a brake job, it’s usually handled by the shop at no cost. It’s easiest to solve by starting over, giving the rotor a fresh surface, cleaning the pads, and driving it again. In some cases, the problem may be a poor choice of friction material rather than anything to do with the rotors.
Brake Pulsation. If the problem is brake pulsation, sometimes there are also underlying issues. Brake pulsation is caused by a parallelism problem between the two braking surfaces of the rotor, essentially the thick and thin spots in a rotor.
This usually begins with run-out which is a deviation from true, or more simply a wobble away from the vertical plane. When the brakes aren’t applied, there is a small air gap between the rotor and the brake pads. With enough run-out, however, the rotor can brush the pads slightly on every rotation, which over time wears a thin spot in the rotor.
A number of things can cause rotor run-out. One is a poorly maintained brake lathe; if the rotor isn’t set up perfectly true on the lathe, a wobble is machined into the rotor. Usually, then, it takes a couple thousand miles of driving before a thin spot is worn in the rotor and the brake pulsation appears.
Another possibility is that the hub the rotor bears against isn’t true or has rust or dirt that prevents the rotor from sitting flush. In this case, when the wheel is torqued down, the rotor conforms to the imperfection, essentially causing it to rotate with a wobble and again, eventually wearing a thin spot that causes a brake pulsation.
Frequently Asked Questions
Any time brake pads are replaced, rotors should be measured, then resurfaced or replaced. If there is a brake pulsation problem, that is also usually corrected by measuring the rotors, then either resurfacing them or replacing them.
Sometimes that’s quicker and easier. Some shops might charge less for labor, in which case it can be a decent deal. But in a lot of cases, the labor is the same either way, as is the extra cost of parts. If the rotors measure fine, it is perfectly safe to resurface and re-use rotors.
The two main worries are that there may be rotor run-out, which causes brake pulsation, or that the new pads don’t bed in well, which can cause noise.
No, unless the pads are worn very unevenly. A brake pad with a decent surface will usually bed into a new brake rotor surface without trouble. A general rule in a lot of shops when resurfacing rotors is to reuse brake pads with more than 50% remaining, and replace ones with less.
In most cases, not really. Either way, as long as the work is done correctly and the equipment is well maintained, the end result is, for all practical purposes, the same. An on-the-car lathe is more precise, but any good standard lathe is precise enough, unless a vehicle has hub surface problems.
It is possible, but it’s hard on the lathe and doesn’t always give a good result; rotor manufacturers recommend against it, so a drilled and slotted rotor with a problem is usually just replaced.
Yes, but it’s very hard on the brake lathe bits. A small amount of surface rust isn’t a big issue, but a badly rusted rotor can wear through two or three lathe bits before it’s down to clean metal, and most shops will decline to resurface rusted rotors due to the time and cost involved.