Can You Machine Slotted Rotors

Unless you’re driving a high-end sports car, your car’s brake system is mostly likely equipped with blank brake rotors. Also called smooth or plain rotors, blank rotors work well for most of the driving population, so there’s little reason for most drivers to consider anything else, like slotted rotors. So, what are slotted rotors good for?

Drilled And Slotted Rotor Kits
Can You Machine Slotted Rotors

Are the holes or slots chamfered or otherwise rounded by design? If they are, no you can't machine them, or you will ruin the structure. Ask the manufacturer if you're unsure. Does the machine use a cutting head or a grinding head. Cutting heads work as James stated. Grinding heads work somewhat like a angle grinder, so yes they will work.

For most drivers, blank rotors offer the right mix of braking efficiency and thermal efficiency. If you’re a spirited driver, spend weekends at the track, or tow or haul regularly, slotted rotors can be an improvement. Most slotted rotors feature straight grooves crossing the brake pad path, usually at a tangent to the hub circle. Some slotted rotors also feature curved grooves.

Energy Conversion in the Brake System

The brake system is an energy conversion device. Using friction, the brakes convert kinetic energy (the momentum of your vehicle) into thermal energy (heat), which is absorbed by the brake pads and rotors. The heat eventually radiates to the air or is conducted to other parts of the vehicle, like the wheels, axles, bearings and knuckles. For the average driver, automakers build brake systems to handle a certain amount of heat, how much can be absorbed by the system and how fast it dissipates.

Heat Absorption: Because 70% of braking occurs in the vehicle’s front end, front brakes are heavier than rear brakes, enabling them to absorb more heat. Rear brakes don’t need to absorb as much heat, so solid rear rotors are still common on many vehicles. Some use old-style rear drum brakes for that reason.
Heat Dissipation: To dissipate heat faster, most vehicles are equipped with ventilated front rotors, using airflow to transfer heat to the air. For even more heat dissipation, heavy vehicles, sports cars and work trucks may also be equipped with ventilated rear rotors.

What Are Slotted Rotors’ Advantages and Disadvantages?

Slotted rotors are superior to blank rotors in some ways. Slotted rotor grooves offer two distinct benefits under heavy braking: brake fade, from high-temperature brake pad outgassing, can be significantly reduced, allowing gases to escape through the slots; and the grooves shave off thin layers of brake pad material, reducing glazing and improving braking consistency.

Still, slotted rotors have some disadvantages. Depending on the type of grooving, noises and vibrations are par for the course. The brakes are functioning properly, but their aggressive nature may be off-putting to some drivers. And because of the constant shaving action, brake pad life may be shorter than if they were mated with blank rotors. You may also have a hard time finding someone to machine slotted rotors, even if they’re thick enough to resurface. Some urban legends die hard — they’re just not as forgiving as blank rotors.

Slotted rotors are available for many vehicle types, even economy vehicles. If you’re hard on your brakes and you can stand to give up a little comfort and longevity, slotted brakes could be your ticket to better braking.

Check out all the brake system parts and accessories available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on slotted rotors, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Image via Flickr.

Benjamin Jerew View All

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.

Rotor Resurfacing/Machine Rotors

Drilled And Slotted Rotor Kits

Brake rotors lose some thickness little by little whenever brakes are applied. People machine rotors to extend rotors life. There are downsides, though. Machining can lead to poorer quality rotors and safety issues, is time consuming, and can be difficult to do correctly.

Can You Resurface Drilled and Slotted Rotors?

You can cut or machine a drilled and slotted rotor. Just set your brake lathe to its slowest setting to avoid any chatter. Whenever replacing your pads, you’ll want to replace or cut your rotors, so the new pads can bed-in properly. However, if you want that non-directional cross-cut finish go with a new set of rotors from PowerStop. It’s likely to cost close to the same, and even possibly less than cutting a rotor.

What is Machining Rotors?

Machining rotors can gain back some friction on worn rotors and reduce run-out. Some people even resurface rotors a couple times before rotor replacement. The machining process usually start with sanding the rotors with 120 grit sandpaper to get rid of build-up deposit and dirt. Then cutting, thinning, and trimming the surface of rotors, also known as resurfacing. Finally, testing. Test drive the vehicle to see if the rotors gained some friction back.

Why do people machine rotors?

Can gain back friction and stopping power
Can extend rotor operational life
Reduces run-out on new rotors

4 reasons why resurfacing rotors is concerning?

Reduces rotor quality
Cost and time
Safety
Hard to resurface rotors properly

Reason 1: Quality

Machining rotors make them thinner, susceptible to warping
Machining pushes the rotor thickness to the limit
Thin rotors lead to overheating, warping, vibrating, etc.
When the rotor thickness is different, it results in imbalance, weight shifting, shaking, and vibrating

Reason 2: Cost and time

The cost to machine rotors might be greater than just replacing new rotors
Need to machine both rotors (a full set) to avoid imbalance
Machining rotors might take a couple hours at the repair shop

Reason 3: Safety

Rotor weight needs to be evenly distributed or else it leads to shaking and vibrating
It takes as little as .001 inches difference in thickness to notice when driving and braking
If rotors are machined too thin, they can warp and damage brake parts
By machining the rotors to the maximum level, rotors will overheat, fade, and lose stopping power

Reason 4: Not getting rotors resurface properly

Some repair shops may resurface rotors as fast as possible. This can lead to mistakes in the process or too much metal being shaved off.
Using worn bits to machine rotors may result in vibration
Rotor vibration due to trimming metal off rotors

Tips:

Depending on the rotor condition, replacing rotors is a better option than resurfacing
Check out PowerStop’s high-quality performance brake kits and rotors! Do it yourself, replace your own rotors to save money or bring PowerStop’s rotors to a reliable repair shop.