Do I Have to Turn Rotors When Changing Pads?by Jody L. Campbell
The quick and easy answer to the question is "no." However, this answer is relative to the reason why the pads are being replaced. If the disc brake system has been functioning properly and the pads are being replaced due to wear, you might forgo turning the rotors. An inspection of the rotor should be performed in great detail. Glazing, corrosive rust surfacing, pits, heat spots, grooves or scores should automatically declare the rotor(s) for replacement. But why do many repair facilities turn rotors or replace them when doing a brake job? That answer is a little more complex.
Rotor Warpage and Runout
If the pads are being replaced on the vehicle because of a pulsation or vibration in the brake pedal when applying the brakes, this is due to warpage of the rotor, unevenness of the pads, or excessive rotor or hub runout. Disc brakes rely on friction to perform properly. Ideally, the composition of the pad--much less harder than the surface of the rotor--is going to erode slightly away. But after friction and heat get involved, the surface of the rotor also begins to erode at a much slower rate than the pads. Intense heat caused by poor performing braking systems can create symptomatic changes between the composition of the pads and their relation to the rotor. Rotor runout is the relationship and trueness of rotor to the hub mating surface. If compromised, even replacing or turning the rotor will have little effect, unless an on-car lathe is used to true the rotor to the hub of the vehicle--and even then, will most likely only be a temporary solution to a permanent problem. If a rotor is warped or has excessive runout, replacing just the pads will not solve the problem.
Turning or Replacing
So why do most brake shops and dealerships require turning or replacing rotors when changing pads? The short answer is for customer satisfaction. If the vehicle wasn't experiencing a brake pulsation, but the pads were low and the braking system was working fine--an exception to the rule in most cases--then perhaps just replacing the pads could have been performed successfully. But many customers don't know much about braking systems or they wouldn't have brought their car in for service to begin with. So the repair shop decides to avoid a situation where the new pads create more fiction on an old rotor and a problem results. All the customer is going to think is that they just had their brakes done and now there's a new braking problem. It must have been something the brake repair facility did incorrectly. Instead of taking the chance of this occurrence, the repair facility tacks on an extra charge to either turn the rotors or replace them.
Ideal Disc Brake Job
The best chance for non-problematic results when replacing brake pads is to replace the rotors. While many do-it-yourself mechanics may disagree with this because they've performed conventional "pad-slaps" without incident, let's explore this statement on a do-it-yourself level. Not many people have a brake lathe sitting in their home garage. In order to have the rotors turned, you're going to have to remove them. Once they're turned--for a charge of around $10 to $20 a piece-- they have to be reinstalled. Now the rotors are a little thinner than they were and if a problem reoccurs during the pad to rotor break-in period, you're going to have to do this all over again, only to find out the rotors are now too thin for turning. Aftermarket rotors have been imported for many years now which has greatly reduced the cost of replacing them. Although the quality of these rotors is sometimes suspect, it has brought down the price of domestic rotors as well to stay competitive in the market. For $20 more or so per rotor, you can usually replace them instead of having them machined or turned and have a new rotor for the new pad to break-in to. The ideal brake job consists of quality brake pads--don't go cheap on the components since you're saving money on labor if you're doing it yourself. Mid-grade brake rotors or even high-grade will be better then low-balling price on the rotors. While you're at it, replace the rattle clips for the pads opposed to trying to clean them and make sure you use a quality brake silicone lubricant or graphite-based anti-seize compound to lubricate the respective parts.
It's your car and your braking system. Many backyard mechanics have successfully performed "pad-slap" repairs on their vehicles without incident. Understand that a pad-slap is not going to magically unwarp a rotor. And once the new pads begin to wear into the old rotor, if too much time has gone by, you might be looking at having to replace pads as well as rotors again. It's your time and your money and in most cases, with most people, time equals money. When a qualified mechanic performs a repair, they may require certain tasks to make sure the car and customer are not going to revisit the facility with a problem after the vehicle has been worked on. They will have the mentality that when they do the job, they're going to do it right the first time.