The Definitive Guide
In a disc brake system, there is one crucial component- the brake rotor or, in another name, the brake disc. Brake rotors are found in virtually every modern vehicle, whether light or heavy. The earlier vehicle models had drum brakes, especially for the rear wheels. That has changed in the recent years as manufacturers turned to disc brakes for all the axles. It is the reason why brake rotors are present in a majority of automobiles today.
With the rotor being such an important component, we thought detailed information about it would be of immense help, so we put up this guide. It is a comprehensive brake rotor guide that examines the different types of rotors. Reading it will broaden your knowledge about the component in many aspects, from what function it serves, the different rotor specifications to the problems to look out for. You will also learn about the process to repair or replace a bad rotor. Let us get started.
Brake Rotor Definition
What is a brake rotor?
A brake rotor is the metal disc that brake pads squeeze against to stop a moving vehicle. These components are only found in the automobiles that use disc brakes. Also known as brake discs due to their circular design, brake rotors mount on the axle, at the wheel hub. If your car wheels have adequate openings, you may see the rotor. It’s the shiny metallic surface that’s bolted to the hub.
A brake rotor is a shiny disc on the wheel hub and that is clamped by the brake caliper.
Brake rotors sit between the brake pads. Until you step on the brake pedal, the rotor remains free to spin and does so seamlessly when the vehicle is in motion. Brake rotors and pads work in conjunction, and one is not useful without the other. That’s why any imperfection in either component can render a disc brake system ineffective or troublesome.
There are different types of brake rotors. The kind that a vehicle uses depends on various factors such as vehicle application, make, model, or the year it was manufactured. The differences occur in the design, type of material, and various other aspects.
Race cars will use brake rotor types that are different from those used in normal road cars. The rotors that heavy vehicles use are also different from those of lighter automobiles. Due to the constant improvements in the rotor design and materials, the brake discs newer vehicles come with may not resemble those used by older models.
The brake rotor became a common vehicle component when manufacturers chose disc brakes over drum brakes. Today, almost every new vehicle features a disc brake system either in the front axle or in all the wheels. This makes the disc brake rotor one of the most common vehicle components today.
Why do manufacturers prefer brake discs? This kind of braking system experiences less brake fade than the drum type. The reason is the better heat dissipation that allows the brakes to cool faster to prevent loss of braking power. Most brake rotors are also lightweight, which helps to decrease the overall weight of the braking system components.
Brake Rotor Function
A brake rotor provides the surface that’s contacted by the pads to create friction and decelerate or stop an automobile. Spinning wheels possess kinetic energy. When you step on the brake pedal, you work a mechanism that pushes the caliper pistons and, therefore, the brake pads onto the rotor surface. The contact of the pads on the rotor results in friction that converts the kinetic energy of the spinning rotor into heat energy.
The heat that results from the action of the brake pads on the rotor dissipates into the air. How efficiently that happens depends a lot on the rotor design. It is the reason why these components come in different constructions. Also, why some rotor designs are appropriate when used in some vehicles and not in others.
Because heat affects the brake pads and causes braking power to drop, a component that works with the pads without hearing up excessively is more desirable. The brake rotor takes up that challenge quite strongly. The disc operates in the open, which significantly increases the transfer of heat. Secondly, the rotor can be designed to have holes, vents or grooves. These allow heat to disperse more easily and quickly, resulting in better braking.
Brake Rotor Diagram
Hydraulic disc brakes consist of brake lines to convey hydraulic fluid, calipers to move the pads, and a surface that is contacted by the brake pads. Here is an illustration showing the caliper, axle, and or brake rotor parts.
The brake rotor in a disc brake system helps to stop a vehicle in this way:
When you place your foot on the brake pedal and push it, you’re essentially operating a lever. The lever amplifies the force of your foot and pushes hydraulic fluid out of the master cylinder and into the brake lines. This fluid travels along the brake lines and hoses to reach the brake caliper.
The fluid pressure causes the caliper pistons to move, thereby pushing the pads to make contact with the brake rotor or disc. Usually, you depress the brake pedal when the car is moving, which means the rotor is also spinning. The squeezing of the pad against the spinning rotor, therefore, opposes its motion. Depending on the amount of clamping force as well as duration, the rotor then spins at a lower speed or stops altogether.
Brake rotors come with different specifications. These specs are essential when describing brake disc rotor quality and condition, and knowledge about them is of paramount importance. Learn about the brake rotor specs in the next chapter.
Brake Rotor Specs
Brake rotors come in different types, with different designs and made from different materials. To operate as required, a brake rotor has to conform to certain standards and specifications. These are specific to a manufacturer and usually stamped or engraved on every rotor. The different specs are explained below.
Brake Rotor Thickness
This means the distance from one face of the disc to another. Every brake rotor has the manufacturer’s indicated thickness when new as well as the minimum allowable for safe use. The 3 types of brake rotor thickness specs are:
- Nominal rotor thickness- the thickness of the brake disc when new.
- “Machine to” rotor thickness- the least thickness allowable when resurfacing or machining the brake disc.
- Discard rotor thickness- the thickness which, when reached, warrants a replacement of the brake disc.
A brake rotor’s thickness can reduce due to a number of factors. Constant braking is one of them where the pads wear the disc out. Corrosion of the rotor’s surface is another cause of thickness reduction. Wear happens when the corroded surface has to be machined to restore braking efficiency.
To determine the thickness of a brake disc, a micrometer is used and measurements taken from a minimum of eight equidistant points radially. The thickness specs of a brake rotor determine how much material to remove when machining the disc. As we have seen, these are different from one rotor to another as well as across different manufacturers.
Brake Rotor Lateral Runout
This refers to the amount of wobble when the rotor spins. A lateral runout happens when the rotor deviates from its plane of rotation due to various reasons which include:
- Variations in the thickness of the rotor as a result of excessive heat or any other damage
- Wheel bearings that are too loose or worn out
- The area between a rotor hat and the hub flange filling up with grit or rust
- A mounting surface that is not even
- Poor rotor installation with uneven torque or overtightened mounting bolts
A wobbly rotor causes the brake pedal to pulsate during braking and the steering to vibrate. This result in uncomfortable driving. The problem can be corrected in a number of ways. Cleaning the surfaces between the hub and the rotor is one of them if debris and rust are suspected to be the cause. Resurfacing the disc makes the surfaces uniformly flat, and will correct uneven surfaces. And if the rotor is excessively damaged or warped, replacing it could be the only or most appropriate remedy
To measure lateral runout, an instrument called a dial indicator is used. It’s a special type of micrometer that features a gauge to show the amount of wobble. Specifications vary from one brake rotor to another, but 0.002-0.005 inches would be suitable values for maximum runout.
Brake Rotor Groove Depth
During the times when braking produces excessive heat, the rotor surface may soften. That allows the hard bit in the brake pads to wear the rotor surface, sometimes causing grooves. These grooves can go deep into the rotor surface, past the allowable rotor thickness. To determine the depth, a micrometer is inserted in the grooves and measurements taken. Generally, grooves that are deeper than 0.1 mm would warrant rotor replacement.
Brake Rotor Parallelism
This is a measure of the rotor thickness variations. In other words, it’s the difference between the highest and the lowest values of the measured rotor thicknesses. A brake rotor comprises two surfaces which must remain parallel to each other according to certain specifications. If the parallelism is lost, the braking action may cause the brake pedal to pulsate.
Rotor parallelism measured using a micrometer from a minimum of eight points on the rotor surfaces. Variance should remain less than 0.03mm. To correct parallelism problem, the rotor surfaces may be machined. This clears any raised spots, smoothing out the surface to restore braking efficiency.
Brake Rotor Material
Manufacturers use six different materials to make brake rotors. Each brake disc material comes with advantages when used in certain applications, which dictates the type in a vehicle. The materials are:
- Cast iron– it’s the most common of brake rotor materials. Cast iron rotors are quite heavy but offer excellent performance which makes them suitable for different vehicle types.
- High carbon– this material is basically iron, but to which carbon has been added to improve certain properties. High carbon brake rotors can withstand heat, resist cracking and dissipate braking heat quickly. High carbon rotors also don’t produce a lot of noise or vibrations during braking.
- Ceramic- ceramic rotors are the highest rated in the automotive industry today for their exceptional qualities. As a result, this rotor material is commonly used in high-end cars. Ceramic brake discs maintain braking force even in higher temperatures, dissipates heat quickly, and a host of other properties.
- Steel– brake rotors made from steel are thin and lightweight. They also possess impressive heat handling capacities. A disadvantage of this material is that it doesn’t make durable rotors, and when warped, can produce annoying pulsations and vibrations.
- Layered steel– this material consists of laminated steel sheets. This construction makes the rotor strong enough to resist warping and results in a long-lasting product. Rotors of this type are popular in the disc brakes of racing cars and rarely in passenger vehicles.
- Aluminum– aluminum is light and offers better heat dissipation than many other materials. However, it melts at a lower temperature. This makes aluminum brake rotors unsuitable for brake applications where a lot of heat is likely to be produced.
The specs of a brake rotor are important considerations. They guide you on the parameters to observe when checking, repairing, or replacing a brake rotor. When you have taken your car to a mechanic, too, and the reason the specs are indicated on the rotor body. In the next chapter, we look at the different rotor types.
Types of Brake Rotors
Brake rotors come in different types. This is necessitated by the different vehicle applications and operating environments. There are the high-speed vehicles such as racing cars, heavy ones such as trucks, light cars, and so on. These demand for brake rotor types with matching capabilities.
One brake disc design will dissipate heat efficiently, while another traps the heat and causes brake fade. Some constructions reduce the weight considerably allowing the rotor to be used in specific vehicles. Still, some designs enable a rotor to withstand braking stress and prevent damage. Let’s look at the types of brake rotors on the market today.
Brake rotors can be one-piece or two-piece.
One piece rotors are a solid body with the hat ( the part that bolts to the hub) cast together with the outer ring. These types of brake discs are easy to make and the most common for replacement rotors. One-piece rotors feature all kinds of design to improve heat dissipation, escape of gas, and other requirements.
The downsides of these brake rotor types include weight and the susceptibility to warping. When exposed to extreme heat, one-piece rotors are likely to distort due to thermal expansion. Modern and high-end rotors of this type resist warping, though. This makes them as good as the two-piece rotors when it comes to handling excessive heat.
Weight is another disadvantage of one-piece rotors. Because they are one solid piece, they tend to weigh more than the two-piece rotors. While that may not be a problem with most cars, the weight makes these rotors unsuitable for certain vehicle applications.
Also known as floating rotors, the two-piece discs feature a hat that’s separate from the other rotor body. The hat is usually aluminum and often features assembly bolts. It allows the rotor to expand thermally and prevents warping in extreme heat situations.
Apart from the ability to resist warping or thermal distortion, floating calipers weigh much less when compared to the one-piece type. This brake rotor design also allows for exceptional heat dissipation making the rotors to withstand constant and heavy braking without losing efficiency.
Despite their benefits, floating rotors have their drawbacks. They are prone to producing a rattle which not many motorists would be comfortable with. These rotors also collect debris on the hat easily, plus they are way too costly wherein compared to the one-piece brake discs. Floating rotors are mostly common in high-end and motorsports cars.
Brake rotor designs are further classified into the following:
Source : http://goworldparts.com
These come in the form of flat discs and feature no holes, slots or grooves on the body. Usually made from iron, these solid rotors are cheap to produce and often the standard type for vehicles straight from the factory. Smooth rotors are lightweight and suitable in the applications where heavy components are not desirable.
Flat rotors offer large braking surfaces, which makes their braking capability high. However, they cannot maintain this braking power for extended periods. This is because they accumulate, heat, gas, and brake pad materials to cause fade and lower the braking force.
The vented rotor features two discs with ribs between them which create vents to allow air to circulate freely. These rotors are thicker than the solid type but provide better heat dissipation. Ventilated brake rotors are the most common for their properties, which makes them the preferred type. They are, heavier than the solid rotors, though, and not suitable where weight needs to be kept at a minimum.
Cross Drilled Rotors
This type features holes drilled through the rotor body. The holes allow heat to leave quickly. Debris, water, and gas also find openings to escape through so they don’t cause a reduction of braking power. The downside of this brake rotor pattern is that it causes uneven wear of the surface.
If used in high heat applications such as racing cars, drilled rotors are more prone to developing cracks. This is because of their average heat dissipation capabilities. They are suitable for the typical street car, though, where it’s unlikely that the rotor will heat up excessively.
Slotted brake rotors, as the name suggests, come with slots or grooves on the braking surface. The slots are meant to aid to remove excess heat as well as prevent a buildup of gas. The grooves are usually patterned to point away from the direction of the rotor’s direction of spin. This helps the rotor to vent out gas more efficiently.
This brake disc design helps to deliver consistent braking due to the excellent heat dissipation properties. The slots also remove brake pad materials away from the surface better, which means better braking power even at higher temperatures. As a result, these rotor types are common in trucks as well as race cars.
A disadvantage of slotted rotors is their shorter lifetime, which makes them less cost-effective. These types of rotors also wear out the brake pads too rapidly when compared to the other designs.
Slotted and Drilled
This rotor design combines slots and holes, offering the benefits of each. Slotted and drilled rotors perform well in different conditions. They work in wet environments, high temperatures, and in situations where consistent braking is required.
These brake discs are common in trucks and other heavy vehicles. Due to their exceptional performance, they feature a lot in high-end cars. Slotted and drilled rotors are unsuitable for use in racing cars.
The dimpled brake disc looks like the drilled type, but the holes are only on the surface and don’t cross the disc’s surface. This design is meant to reduce weight and allow heat to dissipate without affecting the rotor’s strength.
Dimpled & slotted rotors offer almost similar benefits. However, dimples are not patterned to provide efficient venting wear materials, and may not perform as excellently as the grooves in a slotted rotor.
7. Waved/ Scalloped Edge Rotors
This rotor type is not common. The idea behind the waved edge design is weight reduction and better heat handling. However, that has been largely disputed with many claiming that the scallop design only offers appearance benefits.
Let’s now see a comparison of the common types of brake rotors.
Slotted Vs. Drilled Rotors
The use of drilled & slotted rotors for daily driving offers different experiences. Slotted rotors do not transfer heat efficiently and are prone to warping. Drilled rotors dissipate heat better. Gas and dust, too, which makes their braking performance better. But the drilled and slotted rotors pros and cons significantly depend on the application. If used in the average street car, the low heat dissipation property of slotted rotors may not be an issue. It only magnifies if the usage involves longer braking times or heavy-duty braking.
Solid Brake Rotors Vs. Vented
Which type offers better performance? When it comes to handling heat, vented rotors are more efficient than the solid type. That’s because the openings between the discs allow fast and unhindered movement of air. This causes the brake disc to cool quickly and maintain braking efficiency. On the other hand, vented rotors are heavier and not suited for some vehicles.
Slotted Rotors Vs. OEM
OEM brake rotors are mostly the smooth/flat type while the replacement rotors feature slots, drills or dimples. Because the slotted type is one of the most common, car owners doing a replacement are most of the time torn between the two. Unless a vehicle’s braking system experiences constant and heavy braking, a flat OEM brake rotor is usually enough.
Every type of brake rotor offers unique characteristics. The rotors also have different lifespans depending on the material, design, quality, usage, and more. Eventually, the discs wear out and require new ones. When should you replace a brake rotor? Find the answer to that question in the next chapter.
When to Replace Brake Rotors
Brake rotors are made from strong materials and designed to last a long time. But the braking pressures, friction, brake pad materials, heat, and other factors take a toll on the discs over time. In the long run, the rotors develop signs of wear- sometimes even damage.
In this chapter, we will look at the brake disc lifespan, when to change a brake rotor and the factors that cause a brake disc to wear or get damaged. Let us start by looking at how long brake discs can be expected to last.
Brake Rotor Lifespan
The length of time that a brake rotor lasts depends on many factors and varies from one vehicle and rotor type to another. The average lifespan lies in the range of 30,000 to 70,000 miles. As we have seen, this duration is only an estimate and can be shorter or longer depending on various factors.
Reasons that would compel you to replace brake rotors include:
- If the rotor is worn out- every brake disc has it’s minimum thickness as advised by the manufacturer. If wear or resurfacing has removed so much material and the thickness is just about to go below the manufacturer’s minimum, a replacement becomes necessary. The right rotor thickness means better heat handling as well as safe braking.
- If the rotor is warped- warping causes the brake pads to move in and out rapidly when they clamp on the rotating rotor. This vibration transmits through the braking system causing the brake pedal to pulsate and the steering wheel to vibrate. Unless the rotor can be machined to correct the imperfections, this situation calls for a rotor replacement.
- If the rotor is cracked- this problem is most common in the drilled rotors. The edges of the holes develop cracks due to constant heating and cooling of the disc. If these cracks elongate, the situation becomes a danger in the form of failed brakes. Other rotor types can also develop cracks radially along the part that mounts to the hub or even near the edges. Cracked brake discs cannot be repaired and need to be replaced. Solid rotors are usually not prone to this problem
- If the rotor is scored- scoring occurs when the brake pads wear down the rotor surface into grooves. This mostly becomes noticeable if the vehicle owner doesn’t maintain the braking system. When brake pads are not replaced in time, they may wear down to the point of exposing the metal backing. Grooves that result from this kind of wear can be so deep as to warrant rotor replacement.
- If the rotor is excessively rusted- normal rusting may not be a problem as it doesn’t affect braking and can be removed easily. But when a vehicle has been stored for a long period, rust buildup can be so severe that it causes warping when the brakes are used again for the first time. The warping occurs due to the rotor heating differently in the rusted and the unrusted parts. And if the brake disc is the vented type, severe rusting can cause corrosion that affects the structural integrity of the rotor.
Here is a rotor specifications discard chart
Using the above brake rotor wear chart, you can take measurements and determine whether to refinish or replace a brake disc. These values vary across manufacturers so this is a guideline only.
Now that we have looked at how to know when to replace a brake rotor, let us see about the things that lead to that.
Causes of Rotor Wear and Damage
Causes of rapid wear of the rotor include:
- Aggressive driving- if a driver constantly jams on the brakes, one of the results is worn brake rotors. Over time, that can mean a brake disc that needs to be changed. This happens when the worn rotor minimum thickness is reached.
- Poor maintenance of the braking system- brake pads should be replaced before they wear out completely. If that’s not done, the steel backing of glued pads or the metal studs of the riveted pads may contact the rotor’s frictional surface and cause severe scoring. If the resulting grooves are too deep, rotor replace could be the only remedy.
- Severe driving conditions- driving in hilly areas requires the application of brakes every now and then. That causes rapid wear of the brake discs. Driving in traffic in a stop-go situation can also accelerate wear. Over time, the rotors reach the manufacturer’s brake disc wear limit and require to be changed.
Causes of rotor damage include:
- Excessive heat- constant heating and cooling can cause a number of rotor problems. It leads to warping, which is a term used for an uneven rotor surface. Excessively high temperatures can also cause drilled rotors to crack and become unstable.
- Metallurgical issues- when manufacturers use low-quality materials and manufacturing processes, this can show up later as a rotor that breaks down too soon. During casting, the molten material needs to cool at the right pace. If that is not observed, the result is weak spots in the rotor body.
- Excessive machining- the usual procedure to correct rotor surface unevenness is resurfacing. If this reduces the rotor thickness specs below the recommended values, it results in a rotor that’s too thin and prone to damage. An excessively thin rotor could also cause the brake caliper pistons to fall off during braking.
- Not using a vehicle for too long- it could cause the rotor to rust. Too much rust can cause the brake disc to warp among other problems. This rotor damage occurs mostly in the rotors that cannot be machined anymore.
- Incorrect installation- uneven or excessive tightening of the rotor causes lateral runout. That, in turn, exposes the rotor to warping due to uneven wear. The unevenness could be corrected by machining the affected surfaces. But then, there’s a limit to the amount of resurfacing that can be done on a brake disc.
The susceptibility of a brake rotor to damage also mostly depends on its quality, material, and type. High-end rotors will outlast those of low quality. On the other hand, ceramic rotors posses the best characteristics. Although more expensive, they resist damage and last a long time. Some rotor designs also withstand high temperatures and don’t warp easily. The vented type, for example, cool much quickly and can work well in high heat conditions without getting damaged.
Brake disc wear and damage can take many many forms and require either machining rotor replacement. What are the signs for that? Let’s see in the next chapter.
Symptoms of a Bad Brake Rotor
When a brake rotor develops a problem, the results convey in different ways. Some are audio cues, while others may be felt at the foot or in the hands when driving. Being aware of these signs can help you make important decisions. You will not end up replacing the wrong part, plus you can take action early enough to avoid dangerous driving or costly repairs.
Warped rotor symptoms, for example, could help you to tell when the rotor needs resurfacing and wear signs a rotor that requires replacing. In this chapter, we will look at these symptoms and what they indicate.
Signs of a Bad Rotor and Meaning
Symptoms that a brake rotor isn’t in good condition include:
A pulsating Brake Pedal
This is one of the earliest- and most probable- signs that the rotors are in bad shape. The pulsations may happen just when you depress the pedal suddenly and firmly while cruising down a road at high speeds. Sometimes, the pulsations come out distant but distinct when you apply only a little pedal pressure.
A pulsating brake pedal usually results from warped rotors. Imperfections or raised spots on the rotor surface push the brake caliper outwards whenever the pads come into contact with them. Because the rotor happens to be spinning, these in and out movements cause the pedal to pulse relative to the raised points.
Warped rotors also cause the steering wheel to vibrate. That’s because the same vibrations in the disc brake system get picked by the steering system. The intensity of the vibrations depends on the severity of the warp. In the worst of cases, the pulsations can be annoying and a source of driving discomfort. Replacing the rotor eliminates the problem, or the rotor could be resurfaced.
In the same way that warped rotor symptoms appear show vibrations in the braking and steering systems, the uneven surface produces noise during braking. It occurs due to the vibrations caused by the raised spots. In mild cases, the noise may not be high but intensifies when the unevenness is severe. The noise can be a high pitched squeal, or a low hum.
Worn brake rotors will also cause braking noise. This usually comes out as a scraping sound, and appear different from the squeal of a warped disc. Sometimes, the sounds caused by a bad rotor happen even when you’ve not applied any brakes. A word of caution, though. Worn brake pads will also cause these sounds, and you may need to confirm this first.
Longer Stopping Distances
This becomes apparent when, even after pumping on the brakes, the vehicle doesn’t stop within the expected distance. This problem results from several rotor issues. Warping of the disc causes the brake pads to lose contact with the rotor at different points and reduces the effectiveness of the pads to stop a vehicle.
A worn rotor surface that’s excessively grooved or scored will also make contact with the pads less strongly and may result in reduced braking power. This translates into longer stopping distances, especially during high driving speeds. Machining the rotor restores the braking power. In some cases, installing a new brake rotor happens to be the best option.
Marks on the Brake Discs
This is a bad rotor symptom that you can only pick by observing the disc’s surface. The marks may appear as grooves or scoring lines and indicate a rotor that needs replacing. What causes grooves in brake rotors? There are several causes. Brake pads that are left to wear to the point of exposing the metal backings is the most common. The pads score the rotor surface when brakes are applied and cause the grooves.
Whether to resurface or replace a scored rotor depends on several factors. The most important is the discard thickness specs of the particular rotor. If the marks or grooves are too deep, a new brake disc would be the only way to restore the braking surface. Also, if you observe severe cracks as these cannot be fixed.
Another sign that should not be ignored is a blued rotor. This happens when the rotor has been subjected to excessively high temperatures over time. It appears as a bluish surface and could indicate a brake rotor that’s almost about to warp or crack.
Dangers of Driving with Bad Rotors
Brake rotors that are worn or warped may seem to be functional. However, they are risky components that cannot offer reliable braking. Worn brake discs may become too thin and may not disperse heat efficiently. This can cause overheating and warping of the rotor and reduce braking power considerably. It can result in longer stopping distances which are not desirable during emergency situations.
Brake discs that are too thin are also more prone to sudden cracking or breaking. If that happens, the rotors suddenly become ineffective and cannot be relied upon to provide a braking surface. As soon as you pick a warped or worn brake discs symptoms, it’s advisable that you take action immediately.
How do you know that it’s a bad rotor that’s causing the signs we have highlighted here? In the next chapter, we discuss that: how to tell if rotors are warped, worn, or damaged in any other way- either through visual observations or taking measurements.
Troubleshooting a Brake Rotor
Troubleshooting brake problems helps you to determine the faulty component, the type of problem, and other aspects. This enables you to take the most appropriate action that restores the vehicle’s performance. Brake rotors are simple components. They don’t have moving parts or complicated electronics. Not even power cables. Which makes them easy to troubleshoot. The components are also easy to access.
All these attributes make the procedures to check a brake rotor for issues quick and less challenging. You only need a few tools and you’re good to go. Let’s have a look at the process to troubleshoot a brake rotor or disc.
How to Check Brake Rotors for Damage
If you notice any symptoms to indicate a bad rotor such as a pulsating brake pedal, you may need to carry out inspections to confirm the problem. Here is the procedure to do so.
- Park the vehicle in a safe place and on flat ground. Ensure the engine is turned off and the emergency brake set.
- Using a lug wrench, loosen the lug nuts on the wheel without taking them off entirely.
- Jack up the vehicle and use wheel blocks to ensure safety. The tire should be slightly off the ground
- Take out the lug nuts and remove the wheel to expose the rotor and the caliper.
- Remove the whole caliper assembly. There’s no need to disconnect the brake lines from the caliper, only ensure it’s tied up safely on the chassis.
- Inspect the rotor for the following.
Grooves appear as ridges on the frictional surface of the rotor. They are an indication of excessive wear. In most cases, these mean a rotor that needs to be changed.
These can be seen on the rotor surface without any difficulty. They can be as tiny as hairlines to wide openings. Wide cracks should be a cause for worry and an indicator of a rotor that needs to be replaced. Hairline cracks, on the other hand, may not be a major issue.
This is noticeably by looking closely at the edge of the rotor. It mostly happens when the rotor has worn to reach the allowable thickness.
It’s unlikely that rust will escape your eye. Should you find rust on the rotor, determine its severity first. Surface rust doesn’t present any problem and usually comes off when brake pads contact the rotor during. What needs attention is the other type of rust, the kind that’s in excess and causing corrosion. This type of rust doesn’t get removed by braking action and continues to corrode the rotor to the point of weakening it. Should you notice corrosive rust on the rotor, the only option is replacement.
Heat spots or warping
Heat spots result from brake pad material that accumulates on the rotor surface and turns into cementite. This is a very tough substance causes localised heating on the rotor surface.This leads to heat spots which are raised areas that cause vibrations during braking and a weak rotor structurally. If the heat spots on the rotor surface are extensive, a replacement becomes necessary.
You cannot determine the level of rotor warping simply by looking at the surface. You need to use an instrument and a dial indicator is the right tool for that. To use the dial indicator, position it so that the indicator probe touches the rotor’s surface. Spin the rotor and observe the instrument’s dial. The lateral runout should be within the manufacturer’s specs.
You can also use a simple method to find out if the brake rotor is warped. This may come in useful if a dial indicator is not immediately available. Take a ruler and place its straight edge against the rotor’s surface. Check to see if there’s a gap left between the edge of the ruler and the surface of the rotor. A gap indicates warping. Do this on both sides of the brake disc.
Usually, brake rotors will have the values for thickness specs indicated by the manufacturer. The rotor must within those specs for it to function properly and safely. To confirm brake disc thickness, you need a micrometer. Take measurements from different spots and compare the readings.
The least value should be above the minimum thickness recommended by the manufacturer. If lower than that, the rotor needs to be discarded and a new one installed. In the case that a micrometer isn’t available, you can use a side caliper. However, the micrometer is more accurate and the most recommended.
After you have found out about the problem with the rotor, the next step is determining whether to replace it or correct the imperfection. If you decide to replace it by yourself, you may want to know the process to carry out brake rotor replacement. That’s what we will look at next.
Brake Rotor Resurfacing/Repair
Not every damaged brake rotor has to be replaced. Sometimes, the problem is only superficial and can be corrected easily. A few raised spots, for example, can be cleared and a flat braking surface created. Some brake rotors are expensive components, and the cost to buy a new one may exceed the cost to fix it. In such situations, it would make economic sense to opt for repair rather than replacement.
Brake rotor repair is called resurfacing, machining or rotor turning. It prolongs a brake rotor’s life so it can serve you for a few more miles. Resurfacing corrects a vibrating brake system, pulsating brake pedal, and many other problems that result from an improperly worn or damaged brake disc.
What it Means to Resurface a Brake Rotor
Brake rotors may develop uneven surfaces for various reason. This is not desirable as it causes unwanted vibrations and reduced braking efficiency. Unless the rotors have reached the minimum allowed thickness, the surface can be put in a machine that removes the raised parts to create a perfectly smooth surface. This is what’s called brake rotor resurfacing. The procedure creates a new surface, much like that of a new rotor.
Brake disc resurfacing involves removing some material off the surface, at the frictional surface. The idea behind it is to clear imperfections to make the surface uniformly even. This procedure is best done by a qualified person on a lathe. The reason is the high precision that’s required to resurface a rotor correctly, and which only a skilled person can achieve without damaging the surface.
Although not advisable, there are vehicle owners who prefer the DIY way by purchasing a brake disc resurfacing tool. This is a simple machine that can be used to machine a rotor. A better option would be to remove your brake disc, take it to a shop that turns rotors, have it turned to the right levels and specs then re-install it.
Brake rotor machining comes with benefits and disadvantages. Often, the type and level of damage determine whether to resurface or replace a brake rotor. But there are times where you can be in a dilemma as to which option is the best for your situation. Here, let us take a look at the pros and cons of both rotor resurfacing and replacement.
Machining Rotors Vs. Replacing
Resurfacing a brake rotor is significantly cheaper. If you have several bad rotors to repair at the same time, rotor turning can be a financially sound option. But then, machining removes material off the rotor surface and could reduce the thickness considerably. A thinned out brake disc doesn’t cool as efficiently as a thick one, making it susceptible to heat damage such as warping. Such a rotor would also be liable to cracking and breakage.
Replacing a rotor may cost a lot, but suitable if you have the budget for that. New rotors conform to all the manufacturer specifications, which means they offer better performance and for long. Rotor replacement is also more convenient when compared to the hassles of machining, plus it gives you the option to upgrade to a better type of brake rotor.
When to Resurface a Brake Rotor
Resurfacing becomes necessary when:
- The rotor shows signs of uneven wear- this can be a pulsating brake pedal or when you have measured parallelism and found it wanting. Machining removes brake pad material that causes unevenness of the surface. This makes it a perfect warped brake disc repair
- The rotor surface has been scored so much that braking power lessens- turning the rotor on a lathe removes corrosion that may be pitting the surface as well as the scoring marks made by worn brake pads.
- Your projected budget doesn’t allow for rotor replacement- machining the rotor saves you a lot and you can have your car’s braking system running as efficiently as before.
- The rotor already has enough thickness and machining will present no harm- when considering brake disc repair, the thickness of the rotor can limit you. If it doesn’t fall well within the manufacturer’s minimum, resurfacing may not be an option.
If for one reason or another you settle for resurfacing, it’s recommended that you take the rotor to a professional. It’s way safer than purchasing a brake disc resurfacing kit and risking damage to the rotor surface. And if all signs indicate a brake rotor that cannot be resurfaced, it’s advisable to install a new one. Learn about how to do that in the next chapter.
Brake Rotor Replacement
Replacing a brake rotor gives new life to the brakes. In most cases of brake disc damage such as warping, replacement offers a longterm solution. Generally, you know that a brake rotor requires replacing if you notice excessive wear or damage. Damage could be in the form of deep scoring or raised areas that are too pronounced. Also, if the wear has reduced the brake disc thickness so much that machining it risks exceeding the discard thickness specification.
Unlike brake rotor resurfacing, replacing a brake rotor is a simple process that can even be a DIY task. You do not need any special skills, and neither do you require many tools. Here is how to do it.
The procedure to Replace a Brake Rotor
Removing the old rotor
- Loosen the wheel’s lug nuts, but only slightly.
- Jack up the vehicle and remove the wheel. This will enable you to access the rotor.
- Remove the caliper by unscrewing the mounting bolts and detaching any clips.
- Use a string or wire to hang the caliper out of the way and avoid damage to the brake line.
- Now, you have full access of the brake rotor. Use your hands to pull it off the hub. In some rotor assemblies, you may have to remove a nut and bearings first. If the rotor has been there for a long time, it may be firmly stuck due to dirt and corrosion. You may have to use a wooden or rubber mallet to loosen it up.
- Once the old rotor is off, clean the hub surfaces to remove dirt, rust and any other material. This will allow the new rotor to mount correctly.
- Inspect other parts of the hub where the new rotor will mount such as the grease seals and the bearings. Ensure everything is in good condition.
Mounting the new rotor
- Clean the new rotor to remove oil and coatings. You can use a brake cleaner for this and a piece of cloth to wipe off the surface..
- Slide the rotor over the studs on the wheel hub. If the hub features a nut that you had removed earlier, replace it at this point.
- Reinstall the caliper taking care to return everything to its right place.
- Replace the wheel and tighten the lug. Once you have removed the jack, tighten the nuts on the wheels once more.
- Perform a brake test and get a feel of the braking performance of the new rotor. Braking should be smooth, without any vibrations or pulsations, and the vehicle should not take long to stop.
Brake rotor Replacement Q & As
1.What is the average lifetime of a brake rotor? – it depends on driving habits, driving conditions, rotor quality, and vehicle applications. The average marriage is usually 30, 000 to 70,000 miles but which can vary due to the factors mentioned.
2.Can you change brake pads without changing the rotor? -yes, you can. Brake pads are made from a softer material than brake discs. As a result, they wear at a faster rate and require frequent replacements. Often, many vehicles owners find they have to replace the pads as many as three times before they need to change the rotor.
3.What is the average rotor replacement cost?- it depends on the type of rotor, vehicle, and the labor costs in the particular region. Expect to pay a few hundred dollars to have a rotor replaced but which can be higher if the rotor model is high-end. Carrying out the replacement yourself can save you more than a hundred dollars.
4.Is brake rotor resurfacing better than installing a new one?- it is, but only in terms of cost. Resurfacing only prolongs the rotor lifespan for a limited amount of time. That’s because it thins the rotor and subjects it to damage by heat.
How long do brake rotors last after resurfacing?- again, that depends on the conditions and usage the machined rotors are subjected to. It also depends on the wear or level of damage before the rotor was turned. Brake rotor machining exposes the surface to warping risk due to the reduced ability to handle extreme temperatures. The rotor cannot, therefore, be expected to last for long.
5.Do new rotors need to be resurfaced? – this is often a controversial topic. Some manufacturers advise against machining new rotors, saying the components are ready to be used in the condition they come in. Others recommend that vehicle owners turn the rotors before installation.
But then, there are rotors that do not come with ready frictional surfaces and if not machined, do not break-in properly. That can result in problems with brake pad materials and cause raised spots that lead to vibrations and weak braking. If the new rotor comes with a smooth surface, you may not need to turn it before installation.
6.What is the idea behind sanding rotors for new pads?- this is usually necessary when you install new pads on an old rotor. Basically, sanding helps to remove raised spots and improve the surface finish. The result is fast seating of the pads and a better feel at the pedal when braking. Removing raised spots also helps prevent rapid or uneven wear of the pads.
Replacing a brake disc offers many benefits. Unless the costs and the nature of damage don’t make installing a new rotor necessary, it remains a better option. Often, the replacement process is simple and doesn’t take many steps. You can do it yourself or, if unsure, seek the help of a mechanic.
Brake rotors are simple components yet among the most essential in the brakes of modern automobiles. Proper maintenance of the brake rotor is, therefore, paramount. It ensures the braking system performs at an optimum and consistently. Taking care of this component requires that you have adequate knowledge about it, and we hope that this brake rotor guide provided you with that.
You now know what function the brake rotor serves and the different designs that you will find on the market. You also understand what braking problems are caused by a bad rotor and how to go about correcting them. Furthermore, you can now make a wise decision when choosing between resurfacing and replacing a failing brake disc. And if you have to install a new one, what rotor type suits your vehicle application and driving conditions.