It’s usually fairly obvious when you should replace your disc brake pads. You may hear the squeal of of a brake pad wear sensor or see the brake pad warning light on your dash. But disc brake rotor replacement is a much different story. It may come as a surprise to learn that disc brake rotors are indeed a wear item. Even though they are made from thick metal they are designed to be replaced after certain wear criteria are met. Here are some signs that you may need brake rotor replacement, along with tips on ruling this problem out:
Aside from the brake pedal pulsation one feels when the ABS engages, stepping on the brakes should not generate any other noise or vibration, that is, as long as brake rotor runout is less than a few thousandths of an inch. Brake rotor runout is the amount of “wobble” a rotor has as it turns. Ideally there should be no wobble at all, but the brake system can compensate for a tiny amount.
Generally, brake rotor runout, over 0.005 inches (0.13 mm), can cause brake pedal pulsation and even steering wheel vibration while braking. Brake pedal pulsation symptoms don’t necessarily require brake rotor replacement, but could certainly indicate an issue. Your local NAPA AutoCare Center can tell you for certain if runout is an issue on your vehicle. They will use a special dial that is anchored to a solid point and can measure brake rotor runout.
Long braking downhill or riding the brake can easily deform a brake rotor, typically referred to as a warped brake rotor. Resurfacing or machining a warped brake rotor may solve the problem, but the uneven removal of material may actually cause it to warp again. There is also the possibility that the warping is so extreme that a large amount of material would have to be removed thus rendering the rotor unusable. In this case, brake rotor replacement may be the only permanent solution. If your brake rotors are indeed cooked, make sure to perform a brake fluid flush just to be safe.
Rust scale and buildup on the wheel hub can keep the brake rotor from seating properly, mimicking a warped brake rotor. Take time to clean all rust and grit from the wheel hub and rotor mounting hole, then try installing the rotor again. If the hub and rotor are clean, but runout is still unacceptable, rotor/hub indexing may cancel out the tolerances in both, resulting in a nearly perfect runout measurement. It may take some trial and error to find the right rotation, but it is worth the time.
Some untrained mechanics, both “professional” and DIY, simply impact gun lug nuts down tight, without a single thought as to proper torque or tightening sequence. (Pro Tip: impact wrenches are commonly NOT torque-calibrated, ergo “torque sticks” are not calibrated and can lead to under-tightened lug nuts.) On many vehicles, this can easily deform the hub or rotor due to the extreme forces involved, leading to brake pulsation. Lift the vehicle, loosen the lug nuts and then use a torque wrench to tighten each fastener in the proper sequence. You can also swing by your local NAPA AutoCare Center to make sure your lugs are tightened correctly.
Just like brake pads have a minimum thickness, brake rotors also have a minimum thickness. If the rotors have been machined more than once, double check that they are still above the minimum thickness. Measure three places on the rotor, using a brake rotor micrometer. Also, make sure that the rotors are not tapered from the inner tracks to the outer tracks. If machining will take them below minimum thickness, then replacement is required for maximum safety and longevity. A rotor that is too thin will overheat much quicker than normal, leading to possible brake rotor warping.
Rotor surface condition may also indicate that it’s beyond machining. Deep ridges and excessive rust may not be impossible to machine, at least not without ruining the brake lathe or exceeding minimum rotor thickness. Blue spots and cracks in the rotor surface, typically from overheating, should never be machined, as the temper has already gone out of the metal. Some flash rust can be expected on the rotor surface after a vehicle sits, but any heavy rust scale should be inspected to make sure the rotor is still sound.
Other problems can cause brake pedal pulsation, such as loose ball joints, wheel bearings or tie-rod ends, stiff CV-joints or worn control arm bushings. Be sure to check the entire front suspension for worn components before jumping on the brake rotor.
Need Brake Rotors?
Fortunately, replacing your brake rotors usually doesn’t add much to a brake pad replacement. For most vehicles the brake rotor simply slips onto the wheel hub, but there are exceptions. There may also be complications if the brake rotor is part of the parking brake system on a rear wheel. If your brake rotors indeed need replacement, be sure to purchase a quality rotor, mount it cleanly, double-check runout (index if needed) and properly torque all fasteners. Always replace brake rotors in pairs so that braking effort will be even. Also pay attention to wheel direction as some rotors are meant to turn a certain way to maximize cooling.
Check out all the brake system parts available on NAPAOnline or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on brake rotor replacement conditions, chat with a knowledgeable expert at your local NAPA Auto Parts store.
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Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.