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Diagnostic: When Should I Replace My Vehicle's Brakes?
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By APF
Brake rotors may be replaced for a variety of reasons. One is that replacement is a must if the original rotors are worn out. Every rotor has a minimum thickness or discard specification cast or stamped somewhere on the center hat section of the rotor. When the brake pads are replaced, the rotors always should be measured with a micrometer to determine their thickness. If the rotors are worn too thin and are at or below the minimum or discard thickness (or they cannot be resurfaced without exceeding the limit), the rotors must be replaced.
Worn-out rotors are dangerous for two reasons: Thin rotors cannot absorb and dissipate heat as well as new rotors, which increases the risk of the pads getting too hot and fading with prolonged or heavy braking. Also, thin rotors are more likely to crack and break apart, which would cause brake failure.
Another condition that usually calls for rotor replacement is when the rotors are “warped” and are causing a vibration or pulsation when the brakes are applied. Warped is actually a misnomer, because the rotors are not distorted but are worn unevenly. When there is more than a couple thousandths variation in rotor thickness, it pushes the pads in and out when the brakes are applied. The force is transmitted back through the caliper pistons, brake lines and master cylinder all the way to the brake pedal, creating a vibration or pulsation that can be felt by the driver. The greater the variation in rotor thickness, the stronger the vibration or pulsation. It’s a really annoying condition, though not necessarily an unsafe one. It may be mistaken by the vehicle owner for a problem with their antilock brake system, which also can produce pedal pulsation or vibrations when the ABS system kicks into play.
Uneven rotor wear and thickness variations can be caused by severe rotor overheating (a dragging brake pad or stuck caliper), by distortion in the rotor caused by uneven torque or over-tightening the lug nuts, or even metallurgical defects in the rotor casting itself. High spots on the rotor will often be discolored with a dark bluish tint. Resurfacing the rotor can restore flat parallel surfaces, but often the hard spots that are caused by overheating or uneven wear extend into the metal surface. Over time, this will cause uneven wear again and the pedal pulsation or vibration to return. Replacing the rotors with new ones eliminates any such worries.
Rotors also must be replaced if they are cracked, damaged or severely corroded. The danger is rotor failure due to the cracks or severe corrosion. Some minor heat cracking on the surface may be acceptable, but heavy or deep cracking is not.
Another reason to replace rotors is to upgrade braking performance and/or the appearance of the vehicle. Drilled or slotted rotors do add a performance look to any brake system, and they also can provide improved cooling for the rotors and venting for the pads. The holes and/or slots provide an escape path for hot gases that can form between the pads and rotor when the brakes are working hard. Holes and slots or wavy grooves in the rotor face also create turbulence, which improves airflow and cooling.
Some vehicles come factory-equipped with “composite” rotors that have a thin stamped steel center hat section mated with a cast rotor body to save weight. This type of rotor tends to be more sensitive to uneven wear and distortion than one-piece cast rotors. Composite rotors also are more costly to replace, so one-piece aftermarket cast rotors are a replacement option. However, if replacing composite rotors with one-piece castings, both rotors (right and left) should be replaced at the same time to maintain even braking and alignment side-to-side. On some vehicles, replacing a composite rotor with a thicker cast rotor also may alter wheel geometry slightly, creating increased toe-out and tire wear when turning.
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By jazroot84
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By Counterman
Bleeding the brakes is a procedure that’s performed to remove air from the system when a component is replaced, and one that’s performed strictly from a maintenance standpoint of flushing or changing the brake fluid. The telltale symptom of air in a brake system is a soft or “spongy” pedal, along with poor brake performance.
The idea and basic process is generally understood: You must get all the air out for the brakes to work properly. Air compresses and fluid does not, so even the tiniest amount will affect brake operation. Bleeder screws at each wheel allow the air to be forced through and out. If the idea sounds simple, it is, but it’s not without the occasional headache.
The key is that not every system responds the same, and you may need to bleed one differently than another. There are a few different methods you can use, and while it often comes down to preference, it pays to be familiar with them all.
The most important thing, however, is your mindset. Don’t think about brake work and bleeding as two different things. Instead, when performing any brake work, think ahead about bleeding and prepare for it. It always should be a part of brake work, as opposed to leaving it as an afterthought.
At minimum, brake fluid should be replaced/flushed every two years. The older it gets, the more moisture it absorbs, the worse it performs and the more corrosive it gets – slowly eating away at the expensive internal components of a brake system. When replacing brake pads, the caliper pistons must be pushed back into
the caliper.
The most common practice is simply to push them back with whatever tool you have at your disposal and remove any excess fluid from the master-cylinder reservoir, but this isn’t the best way to do it. The proper way is to open the bleeder screw prior to pushing the piston back in and let the old fluid be pushed out.
When you force it back into the master cylinder, you’re forcing contaminants and particles back past the master-cylinder seals, which can potentially damage the seals and lead to premature failure. In short, if you’re working on the brakes, get that old fluid out of there!
Bleeder Screws First
The first thing I always do with any type of brake work is check all the bleeder screws and make sure they open. If they’re stuck, regardless of what needs to be done to loosen them – be it heat, penetrating oil or another form of persuasion – now is the time to do it. If you ultimately have one that breaks, you can plan to replace that component as part of the job, instead of waiting until the end only to have one break when you’re
almost done.
Once you’ve opened the bleeder screws, take the additional step of removing and cleaning them. Spray brake cleaner into one end to make sure they aren’t plugged up with dirt or rust. Be sure to wear safety glasses – it often sprays back in your face if they are. Brake fluid should also drip out of the caliper or wheel cylinder, so be prepared with a drain pan underneath. It may not be a lot, but you should see at least a little fluid.
It’s not so important at this step that a lot of fluid comes out, but make a mental note of it. If no fluid comes out, there may be blockage in the caliper or wheel cylinder. It’s not uncommon for rust to form in the bleeder port and keep anything from coming out, even with a clean bleeder screw. If you run across this, it’s a problem that’s easily remedied using a small pick to poke through the rust.
Once you’ve confirmed that all bleeders open and fluid can flow, you’ve set the stage for a successful bleed of the system – but make sure you haven’t overlooked any bleeder screws. Most vehicles have four (one at each wheel). Some four-piston calipers have two bleeder screws each – one on the inboard side and one on the outboard. They both need to open.
Occasionally you may run across a vehicle with a load-sensing proportioning valve in the rear (usually on trucks) that has an additional bleeder screw on top. This can really throw you for a loop because they’re often out of sight. If you don’t bleed the air at this location, you’ll never get a good pedal. The bottom line is to locate all bleeder screws, and make sure they all open and flow freely.
Bleeder screws are located at the high point of a brake caliper, but it’s possible to install some calipers on the wrong side. This is a very common mistake and when it happens, the bleeder screws will be on the bottom. It’s impossible to bleed the system like this, so if you run across it, you’ll have to remedy the situation beforehand.
The ‘Standard’
“Pump it up and hold it!” For most of us, our experience bleeding brakes began as a helper. You pump the brake pedal a few times and hold it. Then the person doing the work opens a bleeder screw. When the pedal reaches the floor, you report “on the floor.” The bleeder screw is then closed, and the process repeated until all air is forced from the system, and you report a good solid pedal.
To properly perform the procedure, you start at the bleeder located furthest from the master cylinder, then finish with the bleeder closest – in other words RR, LR, RF then LF. This method, often referred to as “manual” bleeding, has been the standard procedure for many years, and most likely always will be. It works well most of the time and requires no special equipment.
The drawbacks are that it can be time-consuming and requires a helper, which we don’t always have. You also must make sure you don’t run out of fluid in the process, or you’ll be starting all over again.
The Master Cylinder
Brake master cylinders must be “bench”-bled prior to installing them. Most master cylinders come with a kit of hoses and fittings to connect to the outlet ports. The hoses are then run back to the filled reservoir. With the master cylinder secured in a vise, you can access the piston and use a tool to push it in to fully depress it, which forces the air out and up into the reservoir.
There are many reasons to do this. For one, many master cylinders are mounted at angles that can trap air and make bleeding on the car extremely difficult. Secured level in a vise eliminates this problem. It’s also much quicker. Usually, it only takes five to 10 short strokes to get the air out. When the cylinder is mounted in the car, it takes the full travel of the brake pedal for the same short stroke. It also saves fluid by recirculating it back into the reservoir.
The most important thing to remember is that air can still get trapped in the master cylinder during installation. Usually, it’s forced through the lines and out, but not always. If you’ve bled the brakes and still have a low or soft pedal, you may have air in the master cylinder. At this point, it’s easy to get out. With an assistant holding pressure on the pedal, crack the line fittings at the master cylinder. You’ll hear the sound of the air as it’s forced out. Some master cylinders have bleeder screws for this purpose.
Gravity Bleeding
Gravity bleeding is often overlooked, since the “standard” method over the years has a stronghold on the perception of brake bleeding. Gravity bleeding is simple: Fill the reservoir and open the bleeder screws. Sit back and relax. Gravity will pull the fluid through the system, and the air will travel along with it and out. When fluid continuously drips from the bleeders, your job is done. Theoretically speaking, gravity bleeding should always work, and it usually does.
Truth be told, I rarely use any other method. The problem with gravity bleeding is it can be slow. I usually let gravity do its thing as I clean up from the job. After I get fluid from each bleeder, I close them, pump the pedal a few times to seat the brakes, then open them one more time to release any remaining air. It’s almost foolproof.
Pressure Bleeding
Pressure bleeding is popular among professional technicians due to the speed of it, and the fact that you don’t need an assistant. The drawback is the equipment can be expensive, so you must use it all the time for it to pay for itself.
A pressure bleeder utilizes an adapter that attaches to the master cylinder, then forces fluid into and through the system. The main advantage to pressure bleeding is that it’s quick, but sometimes it’s also necessary. This is especially true on some newer vehicles with antilock braking systems (ABS). Air can get trapped in the ABS valving, and in some situations, pressure bleeding is the only method that will work. The high pressure compresses the air bubbles to the point where they’re carried through with the fluid, instead of hanging up in a crevice while the fluid flows by.
If you work on newer vehicles, at some point you will need a pressure bleeder. A final advantage to pressure bleeding is this equipment stores a volume of fluid, so you don’t have to worry about running out mid-process.
Vacuum Bleeding
A vacuum bleeder attaches at each bleeder screw and draws the fluid through the system. It’s just another way of doing it with the advantage of speed when compared to manual bleeding. Vacuum bleeding also is one of the cleaner ways to do it because you’re drawing the fluid through the system directly into a container. You don’t have to worry about catching the fluid that’s pushed out of the bleeder using other methods.
Auto-Refill Kits
It’s easy to run out of fluid when bleeding brakes. We’ve all done it. A popular option for manual, gravity or vacuum bleeding is a refill kit that connects to the master cylinder and feeds fluid into it through gravity. They usually have a large enough capacity for bleeding or changing the fluid. Are they necessary? No, just a convenience.
Final Tips
Some newer vehicles with ABS have the option to bleed the ABS modulator and valve assemblies with a scan tool. This uses the ABS pump to force fluid through the system. The advantage is getting air out of the modulator. This often is the quickest and most efficient way to do it, but generally it’s not mandatory if you don’t have the scan tool to do it. The same result can be had with a pressure bleeder.
There are two things that are frequently confused – a soft pedal and a low pedal – and it takes experience to recognize the difference. A soft pedal is caused by air in the system, and a low pedal is commonly caused by misadjusted drum brakes, so just be aware of this and don’t confuse the two. With the proper preparation and a little bit of patience, brake bleeding always should be the most routine part of the job.
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By Counterman
It used to be common for mechanics to rebuild certain components in the shop, including brake calipers, wheel cylinders, starters and alternators. There used to be a time when economically it made sense. The small components needed for a rebuild were inexpensive, and it ultimately didn’t take too long. Plus, all you could get was the rebuild parts, or go with new.
But the repair industry shifted away from rebuilding. Now, professional technicians rarely toy with the idea. But what about brake calipers? Does it make sense to rebuild them instead of replacing? Most of the parts are readily available. If the professionals don’t do it, why not? And, can it save money for a DIYer?
The knee-jerk answer for many is no. The main reason is time versus cost. Let’s face it: Remanufactured calipers are very reasonable in price. Companies that do this benefit from volume. Every part of the process from cleaning to inspection, machining and reassembly happens in volume, so they’re able to keep the costs low, yet produce a quality product. It’s difficult to justify the amount of time it would take, especially when you consider the cost of your labor.
Is it difficult to do? Not by any means. A brake caliper is possibly one of the easiest things to rebuild – even rear calipers with built-in parking brake mechanisms. It’s the same basic process (just a few more parts), so you just need to pay closer attention to how they come apart.
But, there are a few questions to ask. Do you have the means to clean and refinish it? Do you have the tooling to properly hone the piston bore? And then you need the seal kit and possibly a new piston. To match what you get with most reman calipers, add new slide pins, boots, pad shims, a new bleeder valve and new brake-hose sealing washers into the mix.
When you consider the time and effort involved, suddenly it starts to sound a little better to go with a reman or new, and the best part is, new calipers aren’t much more expensive than reman.
Why Rebuild?
With all that said, why would someone rebuild a caliper? Rebuilding can be fun and it’s a rewarding feeling. Even though it’s not cost-effective from a professional standpoint, for a DIYer it can save a lot of money. If it’s a project car and time is not of the essence, saving money is usually the name of the game.
Remanufactured calipers are always refinished, but maybe there’s a specific color you want the calipers to be. High-heat caliper paint is readily available in many colors, and if you’re going to paint them, the proper time to do it is when they’re disassembled.
In some cases, on older cars, reman or new calipers may not be available. There aren’t any cores to rebuild, and it’s cost-prohibitive to produce new ones, so you may have no choice on some restorations. There also are cases where a specific type of caliper – whether it be the design or specific casting marks – may affect the originality of a car, and this also is an important part of the restoration.
There are plenty of reasons to rebuild a caliper, and there’s certainly nothing wrong with doing it. But, it’s safe to say that most are going to go with reman or new options unless the circumstance calls for using the original.
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By garryhe
The replacement of link hidden, please login to viewis an important part of car maintenance, as the condition of the brake pads directly affects braking performance and safety during travel. When it is necessary to replace worn brake pads, it is generally recommended to replace the brake pads on both the front and rear wheels together.
Actually, in most cases, it is not necessary to replace the brake pads on both the front and rear wheels together. The wear and link hidden, please login to view of the front and rear brake pads are usually different. Under normal circumstances, the front brake pads experience greater braking force, resulting in higher wear and shorter lifespan. They typically need to be replaced around 30,000 to 50,000 kilometers. On the other hand, the rear brake pads endure relatively less braking force, meaning they last longer. Generally, they need to be replaced around 60,000 to 100,000 kilometers. When replacing brake pads, it is important to replace them together so that the braking force on both sides is balanced.
If both the link hidden, please login to view and link hidden, please login to viewhave a certain degree of wear, it is also possible to replace all four of them together.
When should brake pads be replaced, and how can you perform a self-check on them? Here are the methods:
Check the thickness: A new brake pad typically has a thickness of around 1.5 cm. As they wear over time, the thickness of the brake pad gradually decreases. Professionals recommend that when visually observing that the brake pad thickness is only about 1/3 (approximately 0.5 cm) of its original thickness, it is advisable to increase the frequency of self-checks and be prepared for replacement. Each brake pad has a raised indicator on both sides, with a thickness of around 2-3 mm. This indicator represents the minimum thickness for brake disc replacement. If the brake pad thickness is level with this indicator, it must be replaced.
suggestions：
It is indeed important to consider individual driving habits and environmental factors when determining the replacement interval for brake pads. While a general guideline is around 60,000 kilometers, it is advisable to have them inspected by a professional technician during regular vehicle maintenance when visually observing that the brake pads are thinning. This is because visual inspection can sometimes lead to errors, and a thorough examination by a qualified mechanic is more accurate and precise.
Listen for noises: If you hear a "squealing" sound when lightly applying the brakes, it could be an indication of the initial interaction between the brake pads and the brake rotor upon installation. In such cases, it is recommended to replace the brake pads immediately because they have already reached the limit where the indicator on both sides of the brake pad is directly rubbing against the brake rotor. When encountering this situation, it is important to inspect the brake rotor while replacing the brake pads. The occurrence of this sound often suggests that the brake rotor has been damaged. Even after replacing the brake pads, the noise may persist. In severe cases, it may be necessary to replace the brake rotor. Additionally, the quality of the brake pads can also contribute to the occurrence of such noises.
Therefore, once unusual noises occur during braking, if it is not caused by the brake pads, it is possible that excessive wear of the brake pads has led to direct contact between the brake pad indicator and the brake rotor, resulting in damage to the brake rotor. The cost of replacing a brake rotor is higher than that of brake pads. Therefore, it is advisable for vehicle owners to develop a habit of regularly observing and promptly replacing brake pads when necessary. This will help prevent potential damage to the brake rotors and ensure optimal braking performance.
If you feel a lack of braking power when applying the brakes, it is possible that the brake pads have significantly lost their friction. In such cases, it is crucial to replace the brake pads to avoid potential serious braking accidents.
Therefore, it is important to develop a good habit of self-checking. Additionally, decreased braking performance can lead to increased consumption of brake fluid. Therefore, when replacing brake pads, it is necessary to check the condition of the brake fluid as well. and you should change good quality link hidden, please login to viewor link hidden, please login to view.
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