Why resurface rotors

While your rotors are not necessarily designed to be sacrificial like the brake pads, they too will wear down. They become thinner. And excessive heat from aggressive braking or hauling heavy loads can lead to glazing and hot spots on your rotors. The lifespan of a rotor is affected by the type of brake pads you use semi-metallic pads wear at a rotor more than organic or ceramic pads , the amount of exposure they receive to salt and moisture, and your driving style.

If you tend to ride your brakes or drive aggressively, your rotors will wear faster. The quality of the rotors can also affect how long they last. So your rotors need to be serviced as well. Traditionally, brake rotors were machined, or resurfaced , each time new brake pads were installed.

That means a technician would measure the rotors to see if they met the minimum thickness recommended by the manufacturer. If they did, and if they had enough material left for resurfacing, the technician would disassemble the brakes, remove the rotors, install them on a machine brake lathe , and remove just enough material to make them smooth again and spin true.

But brake rotors of the past were heavy and thick. They had enough material thickness to undergo multiple resurfacing events, therefore lasting through several brake pad replacements. That means they are thinner than rotors of yesteryear and often do not have enough margin for resurfacing.

So rotor resurfacing, though still performed frequently in fact, new machines, such as on-car brake lathes make the process more efficient and precise , is not quite as common as in the past.

Still, if a rotor is determined to have sufficient thickness for resurfacing and is not warped or cracked, resurfacing is still an option. When is resurfacing an option? When a technician measures a rotor and finds that the tolerances are within an acceptable limit for the procedure.

Otherwise, replacement is necessary. But sometimes replacing a rotor is a better option from the start. For instance, the cost of many rotors today is far less than in the past.

A significant rotor thickness difference in either can cause the brakes to pull to one side. While rotor resurfacing is an easier brake job, replacing rotors is now more affordable than it used to be. Most original equipment rotors were designed with enough thickness for at least two brake pad replacements , but newer cars tend towards thinner rotors to save weight.

Additionally, some rotors are meant to wear down together with the brake pads, so resurfacing might not be an option at all. Whatever you choose, make sure to get the opinion of a reliable mechanic as the rotor is an essential brake system component, and you need it functioning at optimum capacity.

The rotor, brake pads , and caliper are the main brake components in a disc brake system. The brake rotor also called the brake disc is a heavy metal disc connecting the vehicle wheel to the wheel hub. When the wheel rotates, the brake rotor spins with it. The brake caliper is suspended over a section of the rotor. During braking, brake fluid transfers pressure from the brake pedal, engaging the brake caliper.

The brake caliper then clamps the brake pads onto the brake rotor, generating friction to slow the wheel to a stop. Note: The brake rotor and brake pad are only used in disc brakes. In a drum brake , friction is created by pushing a brake shoe against a brake drum instead. You might have a rotor problem if you notice vibrations in the steering wheel or brake pedal when braking.

Sometimes there could even be strange metallic noises when you apply the brakes. Rotor runout defines how much the brake rotor deviates from side to side when viewed from its front edge. Excessive runout can cause the rotor to wear unevenly, producing vibrations during braking. Resurfacing the rotor with a brake lathe also helps correct the runout. This is easier to do with an on-car lathe than a conventional bench or machine lathe. Using a torque wrench instead of an impact wrench to give a final tightening to each lug nut prevents distortion in the hat section, inhibiting rotor disc wobbling.

Cleaning the inside of the rotor hat and the face of the hub using a drill-powered brush before installation will remove dirt and corrosion. If your vehicle was initially equipped with composite rotors with a separate hub and disc section , they could usually be replaced with cast iron rotors. The hat section is thicker, and this can affect the steering and handling of some vehicles. Remember, braking friction generates a lot of heat.

The disc section of the rotor absorbs the heat and dissipates it via cooling fins or vents between the faces of the disc. To reduce costs, General Motors reportedly deleted chromium a rust-inhibiting ingredient that has been used in some of their cast iron rotor alloys.

The result has been some severe rusting problems with GM original equipment rotors. Rust is bad because it weakens rotors over time, and makes the brakes noisy when the vehicle is first driven after being parked. Rusty rotors also increase brake pad wear. The pads will usually scrape the rust off after a few stops, but until then the rust is interfering with the pads and reducing their stopping ability.

Heat Effects Heat management is another factor that affects both rotor wear and braking performance. When the brakes are applied, friction generated by the brake pads rubbing against the rotors creates a lot of heat.

The heat is absorbed by the disc portion of the rotor, and is dissipated by the cooling fins slotted vents between the faces of the disc. Vented rotors are almost always used for the front brakes, while vented or non-vented rotors may be used in the back where braking loads and heat are usually less. The number, spacing and shape of the cooling fins also is important because some designs are more efficient than others.

Replacing original equipment rotors with ones that do not cool as efficiently because of reduced fin count or fin design may cause the brakes to run hot and increase the risk of brake fade.

Advertisement Aggressive driving, pulling a trailer, hauling heavy loads or mountain driving all can cause brake temperatures to soar. Over time, this will increase both pad and rotor wear, requiring the brakes to be serviced sooner than would be necessary with more normal or light use highway driving.

The pads and rotors on vehicles that spend most of their time driving in stop-and-go city traffic will always wear out much sooner than vehicles which are driven mostly on the highway or in light city traffic. Rotor Inspection When brake pads are replaced, the rotors should always be measured to see if they still have enough metal left for safe braking. Advertisement On the other hand, if the rotors still have plenty of metal and show no evidence of hard spots, cracking, severe grooving or rusting, and there are no complaints about pedal pulsations, the rotors can be resurfaced as needed to restore a flat, smooth friction surface.

Resurfacing Issues In some cases, rotors may not have to be resurfaced when the pads are replaced. If they are relatively smooth with minimal grooving, they may not need to be cut. Advertisement Resurfacing a rotor obviously removes metal, making the rotor thinner and reducing its remaining service life. Because of this, some consumers as well as some vehicle manufacturers say rotors should not be resurfaced every time the pads are replaced unless the rotors are badly grooved or uneven.

Okay, some people are cheap and are trying to save a buck. But do they really want to cut corners on their brakes? Resurfacing restores a flat, smooth surface that provides the proper friction characteristics, minimizes noise-producing vibrations and allows for maximum pad contact. Installing new pads on a grooved rotor causes the pads to ride on the high spots of the rotor. Eventually, the pads will wear down and make full contact with the rotors as they seat in.

But this increases pad wear and decreases overall pad life. So it could also be argued that not resurfacing the rotors is counterproductive to maximizing brake life.

Advertisement The surface finish on the rotors also is important because it affects the friction characteristics of the brakes, pad seating, break-in, wear and noise. Most new OEM rotors today have a surface finish between 30 and 60 inches RA roughness average , with many falling in the 40 to 50 RA range.

If rotors are resurfaced, they should be cut to meet these specifications using sharp lathe bits and proper rotation and feed speeds not too fast! Composite rotors those with a stamped steel center hat and cast iron disc that are being resurfaced must be supported with bell caps or adapters to prevent them from flexing while they are being cut. A vibration dampener should also be used on all types of rotors to reduce noise and tool chatter.

Just Replace Them? Advertisement New rotors should be ready to install right out of the box. It will also reduce the thickness of the rotors, shortening their useful service life. For customers who are more concerned about braking performance and safety than saving a few bucks, recommend premium-grade replacement rotors. Premium rotors typically use the same casting configuration as the original same number of cooling ribs between the faces and same pattern.