How to Tell When Brake Rotors Need to Be Replaced

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How to Tell When Brake Rotors Need to Be Replaced

One of the major purchases a consumer will make is that of an automobile. After investing that much money in a product, it only stands to reason that the purchaser would want to keep the vehicle in optimum working order to maintain proper function and safety. One system that is often overlooked until serious issues arise is the braking system, and more specifically, the rotors in the braking system.

The purpose of this guide is to give an overview of the function of the rotor and offer a list of warning signs that would let you know a problem is occurring. Suggestions are made of what should and should not be done if any of these warning signs are noticed. For those who prefer to do their own car maintenance, shopping options will be discussed of where parts and supplies may be purchased, included Internet sites like eBay Motors. By following the suggestions in this guide, a car owner should be able to keep their vehicle in safe operating order for several years.

The Function of a Rotor

A rotor is a part of a vehicle's braking system. It is roughly shaped like a flat-bottomed bowl with a wide lip at the top. The calipers and pads of the brake press against the sides of the rotor when the brake is applied, causing friction to stop the vehicle. The design of the rotor allows the heat produced by this process to be evenly dispersed throughout the braking system so it does not overheat. Normal use of the brakes will eventually wear the various parts of the brake system, and if they are not checked and replaced regularly, damage can occur. If this damage is not addressed, it can progress to the point that the brakes are ineffective and might totally fail, putting the vehicle and its occupants in danger. The good news is there are easy ways to tell if a rotor is bad so the owner may seek services to correct the problem.

How to Tell if a Rotor is Bad

Through everyday use, parts in the brake system wear, particularly the brake pads. When the brake is applied, calipers push the pad against the wall of the rotor causing friction, which slows the car and allows it to stop smoothly. Because of this friction, the brake pads begin to wear down. If the brake pad ever wears below a quarter of an inch, it needs to be replaced. The best way to know if the pad is wearing too much is to look at the brake pad through the space on the wheel. Another way is through the high-pitched sound the brake will make when it is applied. There is a small metal shim called an indicator that will create this sound every time the brake is applied if the pad has worn down too far.

Road Test

A simple road test is another option for testing the braking power of a vehicle. To do this, the vehicle should be taken to a deserted road. Begin driving, and when the speed reaches 30 mph, apply the brakes heavily without completely stopping or squealing the tires. If there is a severe warpage of the rotors, a pronounced vibration will be felt. If no vibration is felt, begin to drive again. When the speed reaches 60 mph, apply the brakes heavily again as was done at 30 mph. If a vibration is felt now, it indicates there is a slight warpage in the rotor that can only be felt during high-speed braking.

By replacing the brake pads regularly, damage to the rotor may be avoided, but ignoring these early warning signs or damage to the rotor caused by dirt or sand getting on the brake pad and grooving the rotor when the brake is applied can cause irreparable damage and the rotor will need to be replaced.

Basic Warning Signs

There are basic warning signs that will alert the driver to problems in the braking system. If any of the warning signs are experienced, the driver needs to take immediate steps to have the system looked at and repaired.

Warning Sign



A high pitched noise that occurs regularly when the brakes are applied


A nonresponsive or "sinking" brake that indicates a leak in the system


Vehicle pulls to one side when the brake is applied indicating uneven wearing of the brake pads or foreign matter in the brake fluid

Grinding or growling

A loud metallic sound indicating pads that are completely worn down and are scratching or scoring the rotors


A pulsation felt when the brake is applied; if felt in the pedal and steering wheel, it is the front brakes; if felt in the seat and pedal, it is the rear brakes

Since many of these warning signs indicate damage to the rotors, immediate attention should be given. There is a minimum, specified thickness designated for the rotors. If the problem is found early enough, a professional machinist can "turn" the rotor and remove the damaged surface while still leaving a safe rotor thickness. If the warning signs are ignored, the rotor will become so damaged that it wears to an unsafe thickness, and compromises the braking system. At this point, the only safe alternative is replacing the rotor.

What Needs to Be Done

When a car owner first hears a squealing sound as the brakes are applied, it is important to pay attention to whether the sound occurs every time the brake is applied or not. If the car has been sitting for a while after being exposed to water such as rain or washing the car, the rotors may slightly rust. This is a normal occurrence and the brakes may squeal the first few times after this exposure occurs until the rust wears off. If the brake pads are wearing to the point of replacement, the squealing sound will happen every time the brakes are applied. If this is the case, the owner can purchase brake pads and replace them fairly easily, or they can take the car to a reputable garage for replacement. Any of the other warning signs usually indicate damage to the rotor. This damage will probably need to be addressed by a garage.

Putting New Pads on a Bad Rotor

There are times when a car owner knows the rotors are bad and need to be replaced but finances are tight. They may try to replace the more inexpensive brake pads, hoping this will address the problem for a while. In actuality, it is just as bad or worse.

The brake pad relies on friction as it is pressed against the rotor to help stop the car. If a new brake pad is put onto a vehicle with damaged rotors, the pad will only contact the highest points on the surface, which will reduce its stopping ability. Deep grooves that have been cut into the rotor will act much like a cheese grater and shred the pad material as it is pressed against the rotor.

Another side effect will be an increase in the heat caused by the malfunctioning parts. Since the rotor is no longer able to evenly distribute the heat generated by the braking process, hotspots will occur, indicated by a blue color on the rotor. If evidence of this overheating is found on the rotors, there is no alternative but to replace the rotors.

Purchasing Brake Supplies from eBay Motors

For those simpler jobs like replacing brake pads that can be done to prevent rotor damage, it is possible for the consumer to buy the pad indicated for their make and model of vehicle from eBay Motors and do the repairs as a DIY project. It will be necessary for the vehicle to be placed on a flat surface. Using a jack, lift the vehicle and put jack stands under it to hold it up. Some special tools are required to adequately complete the job. These supplies, along with anything else related to automobiles are available in great quantity on eBay Motors.

When you enter the eBay Motors site, you will find a vast assortment of brake parts available for purchase. All you have to do is type the part you are searching for into the search bar on any page. Including make and model of the vehicle will help narrow the search and help to ensure you receive the correct part.

An Up-close View

For a closer look at the product you are considering buying, eBay offers a picture zoom feature. If you click on the thumbnail picture, a larger version of the picture will be available. In this environment, you have access to other information about the product, the seller, and customer reviews. If you hover the cursor over the picture, another zoom function is activated, giving a very close-up view of the product features. You can move the view around by simply moving the cursor.


A car's braking system is one of the most important systems in a vehicle. Keeping it in good condition is the only way to ensure optimal performance and passenger safety. The first things to wear on the braking system are the brake pads. By routinely checking the pads and replacing them when they go below the safe operating thickness, you can preserve the life and performance of the entire brake system. Regularly checking the brake fluid is another way to be sure severe damage will not be done to the rotors and other critical parts of the system.

If warning signs are noticed, addressing the issues early will save time and money. Parts may be purchased in brick and mortar establishments or online at sites like eBay Motors. If the damage has gone beyond simple part replacements, visiting a reputable garage or service department is an option. By addressing these issues in a timely manner, the owner's vehicle will offer years of reliable service.

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