- Can You Machine Slotted Rotors
- Slotted Rotors Benefit
- Slotted Rotor Installation Direction
- Can You Machine Drilled And Slotted Rotors
When you have a pulsation or a comeback, what do you blame? The driver? The pads? Defective rotor? If you’re blaming any of these things, the problem is most likely you.
The main reason that slotted rotors work better than stock is when a brake pad is clamped down on a rotor heat and a gas are created between the brake pad and the rotor. That is what reduces braking force and the slots give this gas a way to escape greatly increasing your pad on rotor contact area and making your brakes stop on a dime and cough up 9 cents change.
Myth 1: Machining rotors is unprofitable
Labor in the shop doesn’t have to be delivered from a parts shop or take up inventory. You just have to make it a line item on the repair order instead of giving it away with every brake job.
Can You Machine Slotted Rotors
Installing new rotorsDOES NOT eliminate the possibility of a comeback. This myth creates more comebacks than it solves. These comebacks often start with blaming the new pads, and ends with the customer having to return a second or third time until someone pulls out a dial indicator and micrometer.
Installing new rotors is not a way to avoid having to use a micrometer or dial indicator. For every brake job, you should always measure for runout (rotor and flange) and the dimensions of the rotor replacement before brake service is performed.
After the rotor is resurfaced or a new rotor is installed, the rotor should be measured for runout when it is installed on the vehicle as a quality control method. A rotor replacement could have excessive runout when it is installed on the vehicle due to a stacking of tolerances
Myth 2: New rotors prevent comebacks and are cheaper and more profitable than an on-the-car lathe
What if the runout exceeds the manufacturer’s specifications when the new rotor is installed on the vehicle? It has often been said that you should never machine new rotors, but in some cases, a new rotor should be machined to match the vehicle with an on-the-car brake lathe.
Using an on-the-car lathe can help to reduce runout on new rotors. The main advantage of these lathes is that they are able to cut a rotor in its operating plane. This means that the rotor is machined to match the hub.
Myth 3: Rotors do not need to be measured
Even if you use new rotors, your chance of a pulsation comeback could be greater than if you left the old rotors on the vehicle. Runout in the hub and new rotor can stack up to cause Disc Thickness Variation (DTV) in a few thousand miles. DTV is the main cause of pulsation.
Runout greater than .005” (±.001 depending on the rotor or flange diameter) is a sign that the flange, rotor and/or bearing should be replaced. The needle of the dial indicator should be perpendicular to the rotor. Measurements should be taken a quarter inch from the edge.
Flange runout can be corrected with tapered shims that are available to correct a runout of 0.003 inch (0.075 mm) to 0.009 inch (0.230 mm). A runout of more than 0.005 inch (0.125 mm) at the bearing flange cannot be corrected by the use of a shim. The combination of rotor and bearing flange could prevent the rotor from being turned. Checking bearing flange runout should be performed after friction surface runout. Changing the rotor position 180º on the bearing can check flange runout. If the high spot changes 180º, the rotor could be OK or ready to turn after the bearing is shimmed.
Myth 4: Two passes make for a better finish
Cutting a rotor in one pass is essential for productivity. For non-composite rotors, it is possible to take as much as 0.020″ per side while still having an acceptable finish. However, with a composite rotor or one with hard spots, the depth should be reduced, likely below 0.010″ per side, for a quality finish. In order to remove this much material, it is essential to have sharp bits.
Cutting too fast will reduce the cut quality and possibly create chatter. A larger diameter rotor will need to turn slower than a small diameter one.
Single-speed lathes are set at the slower speed of the largest application they are designed to cut. This is usually around 0.002″ per revolution.
Poor rotor finish can lead to noise. The two primary goals of machining a rotor are to provide a smooth surface finish for the pads, and provide a true surface finish. Never use the ballpoint pen measurement method when machining rotors. The only real way to measure is with a very expensive and very fragile profilometer that measures the roughness average. The best way to make sure a lathe is cutting rotors the right way is to make sure your cutting bits are fresh, adapters are true and the crossfeed is set properly
Disc Brake NVH
Vehicle manufacturers depend on brake suppliers to do the preliminary testing on the individual components that go into a vehicle’s disc brake system.
Brake Rotor Service Tips
Pads and brake rotors are the foundation of any ABS, stability, or traction control system. Extra attention should be paid when performing brake repairs.
What are the advantages of slotted drilled rotors?
Did you ever wonder if slotted drilled rotors would provide better braking on your family car or truck? Here’s some info right from the experts.
Brake rotor temperatures
When you apply the brakes, the pad’s friction material and rotor convert the vehicle’s motion into heat—a lot of heat. You can calculate exactly how much heat if you know the vehicle weight, swept area of the rotor (the part the pad clamps against), the rotor’s mass, and vehicle speed. If you don’t want to do the math, trust me, it’s hot. In fact, a Formula 1 race car can generate 1,000°F. Most car fanatics figure that since racing cars use slotted drilled rotors and those rotors can handle 1,000°, they must be great for their family cars and trucks. Ah, not so fast. Let’s take a look at the complete picture.
Brake pad fade
When you stomp on the brakes and they heat up, they can reach a critical point called “fade.” At the fade point, the brake pad resins (the material that hold the friction portion together) begin to vaporize, causing a gas layer between the pad and the rotor’s swept area. Think of this like brake pad hydroplaning. I know where you’re going with this; you assume that drilled and slotted rotors relieve the gassing pressure and reduce the hydroplaning effect of fade, right? Well, you’d be a bit off base because modern brake pads are far less prone to this phenomenon than older brake pad formulas.
Braking heat
That doesn’t mean new brake pads don’t generate heat, they do. But the question is, does stopping with ordinary brake pads and rotors generate enough heat to cause fade? Keep in mind that brake heat dissipates two ways; the majority of the heat is removed due to the pumping/cooling action of the rotor vanes, and the rest through the caliper and brake fluid. When brakes heat up to near the fade point, enough heat has already entered the brake fluid, causing it to boil.
Do slotted drilled rotors aid in cooling?
That’s the $64K question and the answer is no. The biggest advantage of slotted drilled rotors is that the holes and slots literally scrape off the face of the brake pads, “refreshing” them with each rotation. They provide a minimal cooling advantage, if at all. Depending on how the slots are designed, that refreshing feature may actually cause the pads to wear out faster.
If you want better braking, get better cooling
Rotor vane design is the single most important feature to look for in a brake rotor because the pumping action is far more effective than the slots and holes. Remember, the vanes are a centrifugal fan that suck air into the rotor near the hub and throw it out the vanes on the rotor’s circumference. Car makers spend a lot of money and engineering time designing these “fans” and that’s what makes OEM rotors more expensive. Factory rotors generally have more mass than economy aftermarket rotors as well. More mass, bigger fans, more vanes all add up to better cooling.
Slotted Rotors Benefit
The downside to slotted drilled rotors
High quality drilled rotors generally don’t crack. But economy drilled rotors do. If you’re going to add them, make sure you buy premium rotors. And be prepared to change your brakes more often since they tend to wear out pads faster.
Posted on by Rick Muscoplat