Brake disc runout causes and consequences

BODY REPAIR SERVICE

Brake disc runout

The “Authority” service center has been engaged in body repair of passenger cars for 10 years, as well as conducting independent examinations in case of accidents.

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Some drivers have encountered a situation where vibration is felt when braking. It can be felt on the brake pedal, steering wheel and the entire body of the car. If you feel vibration when braking at medium to high speeds and it is directly related to the brake pedal, you can be sure that the brake rotors on this vehicle are warped. This defect is called brake disc runout. It often happens that vibration appears and intensifies after several intense braking sessions, as a result of which the brake discs heat up.

Causes of the defect and how to avoid it

Fans of fast driving often encounter this problem, because the main reason for the deformation of brake discs is their overheating. But relatively calm drivers can also encounter this. To minimize the risk of brake disc deformation, you should follow several recommendations.

Try to avoid frequent heavy braking. If you had to resort to emergency braking at high speed, try to calculate the braking distance so that you can drive the last meters only by braking slightly. This will allow the heat to be distributed more evenly across the disk. If you constantly press the brake pedal until it comes to a complete stop, the place where the disc is pressed between the brake pads will heat up more, and there is a high probability of deformation of the disc.

Separately, it is worth recalling that after replacing brake pads and/or discs, the first 100-150 km of the vehicle must be operated in a quiet mode. Try not to accelerate more than 80 km/h. Avoid sudden braking. Do not brake using more than 60% brake pedal force. After 150 km, you can gradually increase the load on the brakes. Depending on the car model or manufacturer of brake discs and pads, the grinding procedure may vary. New pads and discs take time to get used to each other. Until the pads are worn in, the braking efficiency is less, you have to apply more braking force, and this leads to overheating of the brake discs, which may result in deformation of the new discs and the need to replace them. Much has been written on various websites about the need to grind in brakes after replacing discs or pads, but motorists forget about this.

How to get rid of runout of brake discs?

If you do experience runout in your brake discs, there are two ways to solve the problem.

The first is replacing brake discs. This method will definitely help if it is correctly replaced by a competent car body repair specialist. Don't forget to rub in the pads after this.

The second is grooving the brake discs. If there is slight vibration in the car, and during diagnostics at the service center it was discovered that the disc runout is greater than normal, then you can try to sharpen the discs. But this does not guarantee 100% elimination of vibration. And if vibration is almost not felt on cold discs, and strong beating appears after the brakes warm up, then grooving will not solve the problem. This is a waste of money, because cold discs will wear out, and when heated, they will become deformed again. Also, disc grooving is not suitable for those whose disc thickness is equal to or close to the minimum acceptable value. Even if the disks become even, but thinner than the minimum size allowed by the manufacturer, they will still need to be replaced.

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Brake pedal beating, causes, consequences, solution to the problem

Why does the car shake when braking and how to solve this problem?

What exactly is important in the braking system? In fact, everything is important! That is why it is necessary to monitor not only the brake pads and the brake system line, but also the brake discs themselves. What danger does overheated rotors pose? We will answer you briefly.

If, when you press the brake pedal, you feel the pedal beating or a slight but obvious rocking, that is, vibrations of the entire car, then it’s time to check the brakes for malfunction.

Most likely, you are faced with a classic case of brake rotor deformation. The situation needs to be corrected urgently, otherwise it can lead to very bad consequences.

The point is this. Over time, cast iron brake rotors begin to wear thin as braking removes millimeters and grams from not only the brake pads alone, but also from the rotors themselves. As soon as the thickness of the disks reaches a certain value (service thickness limit), their safety margin decreases and tends to zero. Such discs may become damaged. One example is described above. The rotors begin to “beat”.

As discs become thinner, they are subject to greater deformation due to the heat that accompanies their braking.

Sometimes vibration does not occur due to the brake disc, but when the caliper does not press the pads correctly.

Brake rotors “float” even when there is an uneven, sharp temperature change. For example, it’s spring, you’re racing along the road for almost a hundred kilometers, you come around a corner and see a large puddle right in front of the hood. You brake sharply, but do not have time to completely reduce the speed and naturally fly into this puddle of water, raising large sheaves of splashes. And then, the heated braking surfaces of the discs, filled with cool melt water, if their thickness has become critical, can certainly lead to trouble.

The same thing can happen with low-quality discs after such a sharp and long braking. Moreover, in this case, beating may appear even on new disks.

Tip No. 1 From here we draw the first conclusion: do not buy unverified discs from unverified sellers. Try not to overheat the brakes by braking hard.

Further, the thinning of the disc surface can also lead to cracks or cracks in the rotor, which can contribute to the wheel locking and further lead to an accident. This brake problem is sometimes described on forum sites or raised in personal conversations between motorists. It is difficult to say how often brake discs burst; these cases are mainly associated with modern cars, namely because automakers are trying to save as much as possible on the weight of all elements included in the braking system, including by reducing the thickness of the rotors themselves.

The causes of beating can also be:

Uneven wear of discs (“treated” by turning the disc).

Overheating of the brake pads with subsequent loss of parts of the pads or severe wear.

Soured pistons in calipers.

Unbalance of the entire wheel.

Another option is associated not with wear of the disk, but with its incorrect installation. But this type of failure will manifest itself immediately after installing or reinstalling the disks

Tip #2 The problem can be solved in two ways. The first is to remove the brake discs and send them for modification to specialists from a car workshop. The process of processing a curved disk is as follows: the surface of the disk is leveled using a special machine.

True, there is one pitfall here, namely, if the surface of the disk is too thin, then such a procedure is not allowed, i.e. forbidden.

Tip #3. Another and probably more effective option is to buy a new set of disks and replace the old ones with them.

Most often, the front set of brake discs needs to be replaced, since the rear one is the least loaded. At the same time, you must not forget to change the pads, then the problem with the brakes will be resolved automatically.

To prevent this problem from happening again, please try not to overheat the brakes. This is not only expensive, but also dangerous.

Disassembly ABW.BY: the steering wheel was vibrating - was it possible to cope with the problem by turning the discs?

The owner of a 2001 Volvo S60 was brought to the service station by vibration that appeared on the steering wheel when it was necessary to slow down the car while driving at a speed of 70 km/h and above. The owner suggested that the vibration could be caused by the runout of the brake discs, so in the repair request he asked the car service specialists to sharpen the front brake discs.

It is right to respond in a timely manner to the appearance of a problem in the brakes, because the slightest malfunction in the braking system of a car reduces its level of safety and endangers the lives of not only the driver and his passengers, but also other road users.

Why is brake disc runout dangerous? It indicates that somewhere on the working surface of the disk a bulge has formed, or, if you want for clarity, a “wave”, which periodically throws the pad away from the disk. Until the pad, having passed the top of the “wave”, presses against the disc again, the car slows down worse, which increases the braking distance necessary to reduce the speed to a safe value or stop the car.

However, is the correct method to resolve the problem chosen? We decided to take this opportunity to evaluate the effectiveness of turning brake discs, and at the same time talk about what this procedure is, because the discussion of the article “Should I change the brake fluid, should I sharpen the discs?” on the ABW.BY forum showed that there is a need for this.

While the car is being driven onto a lift and being prepared for repair, we ask a specialist at the Libra-2000 auto center, Evgeniy Slepyan , why the brake disc may warp. It is believed that the discs “drive” after driving through a puddle, which causes them to suddenly cool, or when a car with overheated discs, without pausing to cool the brakes, drives into a car wash. Is it so?

“In my opinion, this is not the only reason,” Evgeniy answers. — All cars drive through puddles, in the city most drivers use their brakes with approximately the same intensity, but in some cars the discs warp, while in others this does not happen - why? I think it's not a matter of puddles, but the effect of too high temperatures on the disk. In other words, the disk was overheated - that’s why it failed. And for this, sudden cooling is not necessary.

But during emergency braking from high speed, too much heat is generated in a very short time in the area where the pads are pressed against the disc. The heat does not have time to be transferred to the medium that surrounds the friction zone. As a result, overheating occurs.

Or take, for example, a case where a car has discs and pads of different brands. Manufacturers calculate pads for their brake discs so that they work perfectly together. When the discs are of one brand and the pads are of another, overheating is possible under certain braking conditions.

The second reason is the impact of large mechanical loads. It is difficult to imagine how much force the pads actually exert on the disc during emergency braking. Let's consider this situation: a car brakes sharply, until the wheels lock, in front of an unexpected pothole in the asphalt, crashes into it, but the driver does not release the brake pedal. Next, the wheel hits the sharp edge of the hole. The impact causes the wheel to spin sharply, but at this moment the pads hold the disc with enormous force. Why shouldn't it bend under such conditions? You don’t need much - a few tenths of a millimeter, but they will make themselves felt by vibration on the brake pedal, beating on the steering wheel or body when braking.

To eliminate runout and restore brake efficiency, we offer a service for grooving the working surface of the discs, however, not all discs are suitable for this procedure. First you need to assess the condition of the disk and then make a decision - to sharpen it or definitely replace it.”

The left front wheel has already been removed - you can see what's wrong with the disc and pad. At first glance, nothing.

The disc appears evenly worn. The shoulders on the boundaries of the working surface of the disk have the same height along the entire circumference.

Measurements of the disk thickness in several sections also do not provide any clarity. The thickness is the same - 24.2 mm, so for now only one thing is clear - it is still possible to remove metal from the disk. However, the auto center workers assured us that as soon as the grooving begins, the cutter will show us what is not visible to the naked eye.

The discs will be sharpened using the Disk Aligner 8700 device from Mad (Netherlands).

The device consists of two parts. The first is an electric drive that connects to the hub and rotates it. The vehicle's gearbox is in neutral at this moment.

The second part is the machine itself.

It is installed in place of the brake caliper, which is previously dismantled without disconnecting the brake pipe.

The machine has two cutters. They can be fed over the surface being processed using an electric motor built into the machine or manually.

The machine is ready for work. Here we go?

Once the work started, we really began to see where the disk was bent. Moreover, we heard this from the tonality of the sound, which varied depending on the thickness of the metal that was cut in a specific place on the disk.

The matte spot left after the cutter passed through is the same bulge that vibrated the steering wheel when the car was braking.

It was not possible to level the surface of the disk in one pass. According to repairmen, this happens most often. It happens that 5-6 passes are required to achieve a perfect plane. It is tempting, of course, to immediately give such an allowance for grooving so that the surface of the disk becomes smooth in one pass, but this will significantly increase the load on the cutters and worsen the quality of processing.

The second pass also did not lead to the desired result, but it allowed us to see how the surface of the disk was gradually leveled.

During the third pass, the area of the matte surface remaining after the cutter became even larger, but the ideal geometry of the outer side of the disk will be when the shiny stripes on top and bottom disappear.

After the fourth pass, we finally didn't see them.

Grooving the disc from the inside followed a similar scenario, but required one more pass. The problem was caused by a deep circular depression in the upper part of the disk, which persisted until the last.

The disk is ready. We remove the machine. The thickness of the disc can be assessed again.

The result was 23.3 mm. This means that after processing the disc “lost” by 0.9 mm, but remained within tolerance.

The procedure for turning the left front wheel disc was completed by replacing the brake pads. Why do they need to be replaced after discs have been resurfaced?

“Opposite the place where there was a bulge on the disc, a wear appears on the pad,” says Evgeniy. — Therefore, the old pad will not adhere to the machined disc with the entire surface of the friction lining. What if the client, shortly after leaving the service, suddenly has to brake urgently? Again, the old pads will not only break in, but will also work for the disc. In other words, they will “kill” the result of the work. Therefore, you shouldn’t skimp on replacing pads.”

In addition to the unsuitability of the disc for grooving due to residual thickness, too deep scoring, severe corrosion and other serious damage, the cost of the issue also makes one think about the feasibility of the procedure. It cost the owner of an S60 600 thousand rubles to sharpen the two front discs. Buying a couple of new discs from reputable brands would cost at least a million. However, it may turn out that regrowing is not much cheaper than buying new discs - this often happens with rear wheel brake discs. In such cases, the purchase seems to be a wiser use of money than grooving.

We would probably attribute its duration to the disadvantages of the procedure. It took about two hours to install, configure and machine the two brake discs.

Instead of a verdict

Five days after the tuning, we contacted the owner of the S60 to find out how things were going. It turned out that the car managed to travel about 1200 km. I had the opportunity to check how it brakes from a speed of 120 km/h - everything is fine, the vibration on the steering wheel no longer bothers me.

Sergey BOYARSKIKH
Photos and videos of Olga-Anna KANASHITZ
ABW.BY

We thank the Libra-2000 auto center for advice and assistance in organizing photography

Brake discs: change or sharpen?

Brake discs are expensive consumables. Usually there are enough for two sets of pads. But it happens that they attract attention much earlier - for example, when a noticeable beating occurs due to a sharp temperature change. I drove through a puddle after heavy braking and the rims became warped. Symptoms: vibrations on the steering wheel and brake pedal, which sometimes even spread to the body when slowing down.

Previously, “crooked” disks were retired. Only a few lucky ones were helped out by familiar turners who had turning machines. About fifteen years ago, auto repair shops began to purchase the appropriate equipment, but the work was done at the artisanal level. Only with the advent of new machines did things move into a more or less civilized direction. Grinding discs is inexpensive - sometimes several times cheaper than a set of new discs.

To hit or not to hit

There are two types of grooving machines, and they are installed directly on the brake disc hub. Those that are more expensive are made in a single unit and provide better processing accuracy; such a machine is connected to the hub through an adapter. Simpler devices have a separate unit with cutters; they require more installation time and the cutters are mounted on the brake caliper bracket.

In both cases, the machine itself rotates the hub: the car engine is not running, the gearbox is in “neutral”. The cutters gradually move along the surfaces of the disc - akin to a gramophone stylus, but which moves from the center of the record. In one pass, the cutters remove a couple of tens of microns of metal from each side. Then they are rearranged and the groove is repeated. Usually the disc is completely processed in two or three such passes. Moreover, first the chamfers formed by the operation of the brake pads are cut off - this reduces the load on the machine and cutters and ensures good quality of surface treatment.

Before grooving, the mechanic must inspect the wheels and suspension of the car. Processing cannot be carried out if the wheel bearing has play or rolls. Otherwise, the disc begins to wander between the incisors and you can forget about an even groove. Even if the bearing is only humming, you need to change it first: if the replacement is carried out after the disc has been grooved, there is no guarantee that during subsequent pressing, the hub will fit perfectly straight, and along with it the machined disc.

The discs are checked for residual thickness, runout and the degree of corrosion of the working surface. Too thin cannot be sharpened; they already do not tolerate heat load well. The permissible thickness depends on the specific model and its modification (size of brake mechanisms). The runout of the disk along several radii is checked with an indicator. In fact, this is a measurement of the difference in thickness at different points - it should not exceed 0.05 mm. You cannot carry out grooving if there is deep corrosion: there is a risk that the disc at the end will be too thin.

After grooving, you need to change the pads, otherwise the friction linings that have worked on a crooked disc will kill the treated disc. For the sake of experiment, take such a block and rub it on sandpaper that lies on a flat plane - dangerous depressions will appear on a visually flat surface!

In Moscow, the cost of turning discs for one axle is no less than 2000 rubles. It is recommended to treat both discs so as not to shift the brake balance. For example, the owner of a first-generation Volvo XC90 will pay 2,500 rubles, and for this money they will also change the pads - the whole job takes an hour and a half. Since the price of one new disk is about 4,000 rubles, the benefits are obvious. And the price of high-quality wheels for budget foreign cars is not much lower. And one more thing: even original spare parts for the secondary market are often of worse quality than those that go into the original equipment. This is also why it is more expedient to process the factory part. Give preference to specialized service stations. Their equipment and attitude towards its operation are better than most official dealers. Not to mention the prices for services.

RISK AREA

Cast iron is the most common material for brake discs. And quite insidious: with sudden temperature changes, cast iron noticeably changes its physical properties - hardness, volume and even internal structure. This feature leads to excessive warping of the working surfaces of the disk. Of course, there are more durable analogs (for example, ceramic or composite) that provide better stability and braking dynamics, but their price is off the charts.

The brake disc shield does not protect against water: it gets abundantly on both its surfaces. If a cast iron disc is exposed to too much temperature change, its internal structure may be damaged. Processing on a machine will remove the bent top layer, but after a couple of intense braking (that is, heating and cooling), the surface will move again - this happens in five cases out of a hundred. Only an experienced turner can identify a damaged disk during turning - by the change in the tonality of the rustling sound from the cutters.

More often than not, the inner part of the disc leads more strongly than the outer part. This happens on cars with calipers with a so-called floating caliper: the inner pad is activated first - and, accordingly, this surface of the disc heats up more.

The runout of the front discs usually responds to vibrations on the steering wheel, the runout of the rear discs - on the brake pedal and on the body. The front discs more often suffer from temperature changes (they are more heavily loaded), and the rear discs suffer from corrosion. Vibrations increase with increasing temperature of the disk and the environment - due to the expansion of the metal. Sometimes the noticeable beating disappears in the winter.

Brake disc runout: causes, diagnosis, replacement

The runout of the brake disc, an important element of the entire braking system, should serve as a signal to the car owner about the need for professional diagnostics and troubleshooting. Optimal braking system performance is achieved after proper “grinding in” of the brake pads and discs. Their service life does not have clear regulatory periods and depends on driving style and operating conditions.

Specifications

Manufactured from cast iron in the last century, modern brake discs are an alloy of ceramics and carbon fiber. This makes them lightweight, resistant to temperature changes and resistant to mechanical stress.

They are a rim attached to the wheel hub and perform rotational movements as the vehicle moves. A caliper with brake pads is attached to the disc. When you press the brake pedal, they clamp the disc and, due to friction, stop it along with the wheels. There are:

Non-ventilated, in the form of a homogeneous plate. Currently used very rarely.
Ventilated, they consist of two plates separated by a special cavity. In samples of the inexpensive segment, radial channels between the plates are located from the central part to the edges.
Radial, a type of ventilated, circular ducts have more precise tolerances, which ensures the best cooling.

The disadvantages of ceramic disks include their lower permissible “cold” stopping value compared to cast iron ones. After heating to operating temperature, the positive properties and performance increase. This point must be taken into account when operating the car during winter, subzero temperatures.

Basic faults

The mass of a vehicle carrying passengers and cargo, friction force, high speeds are the operating torques affecting the brake discs. Maximum wear, within the tolerances established by the manufacturer, are the main reasons for their failure.

They represent the “erasure” of the disk surface that occurs during operation. There are two types of wear and tear:

Uniform – characterizes the correct, “careful” driving style of the driver, during which the disc is ground equally along the entire rim.
Uneven - has scratches, indentations that exceed tolerances and roughness, the reason is improper installation of the pads or aggressive driving with sudden, extreme braking.

The last type of wear is the most undesirable for the further operation of the car. In this case, the braking coefficient of the disk has the lowest value. During rotation, it can “catch” the brake pads, which causes their destruction and overheating, spontaneous braking of the car, and further destruction of the hub.

Uncertified, low-quality brake pads installed on a vehicle, their improper assembly and further vibration can increase the rate of wear.

Diagnosis of increased wear

The braking system of cars, high-risk vehicles, bears the greatest responsibility for the safety of the driver and others. Its serviceability should be checked daily, and professional diagnostics should be carried out during scheduled maintenance, at least twice a year. A signal of increased wear of brake discs will be the manifestation of factors such as:

During braking, a characteristic metallic sound (grinding) is heard. It can appear when the brake pads wear out beyond the tolerances, which in the future will lead to runout and uneven deformation of the discs.
When you press the brake pedal with minimal force, the wheels are blocked (jammed) by the brake pads.
Identification, through visual inspection of discs, of cracks, chips, bending and roughness.
Increased vibration with such discs is guaranteed. Significant reduction in brake disc thickness (with uniform wear). Tolerances prohibit the use of disks whose “abrasion” exceeds 3 mm from the factory size.

After identifying the listed faults, it is necessary to take measures to eliminate them. In many cases, they come down to replacing the worn brake disc and pads with new ones.

Replacing an old disk with a new one

If you have free time, certain knowledge and skills, as well as the necessary set of tools, you can replace the disk yourself. Purchase a new brake disc and pads certified for installation on your car model. Follow the instructions below:

Raise the car on a lift or put it on a jack, having first loosened the nuts and remove the wheel to have free access to the parts to be replaced.
Remove the caliper by unscrewing the bolts using a screwdriver. They are located on the back of the disk.
Carefully remove the caliper; if it is stuck, tap it with light blows of a hammer. Do not disconnect it from the brake pipe; the system is under a certain pressure. If its seal is broken, brake fluid may leak, which will require bleeding. Why, experienced mechanics, tie it to the body.
Remove old pads and plates. On some models, before removing the disc it is necessary to remove the caliper mounting. The screws are unscrewed using a screwdriver.
Remove the brake disc. On some makes of cars it may be secured to the hub with a castle nut, which should be unscrewed before removal. Usually, due to elevated temperatures, the disc “sticks” to the hub. To dismantle it, in this case, it is necessary to remove it from its seat with smooth blows of a hammer through a wooden block.

Check the integrity and reliability of the hub fastening.

Installing a new brake disc is carried out in the reverse order:

To clean the surface of a new disc from plaque and rust, use only special products intended for this purpose.
Wipe it thoroughly with a clean, dry cloth.
Carefully slide the disc onto the hub until it stops and secure it.
Install and secure the caliper seat.
Untie the caliper, install new pads in it, press them apart and install them on the disc.
Secure the caliper with bolts from the reverse side.
Install the wheel and lower the car.
Tighten the wheel nuts.

The car is ready for use. Be sure to check the brakes before driving. To do this, in a place that prevents you from hitting an obstacle in the event of a system failure, start slowly. Press the brake pedal in a smooth motion. Braking should occur smoothly and gently. No jerks, vibrations or pedal drops. When the car is moving, there should be no noticeable beating or heating of the discs.

If you want to carry out the brake disc replacement procedure in a professional service, with a guarantee for the work performed, you just need to leave a request on the Uremont.com website. Here you will find the best options that meet your requirements at the lowest prices.

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