Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

• Non-original brake pads often do not produce the same friction as the originals. This requires more effort to stop and thus a lower pedal.
• A rough (greater than 30 micro-inch) finish on brake rotors will require greater brake pedal effort and lower the pedal.
• Contamination on the brake rotor or pads, such as greasy finger marks can increase pedal effort.
• Air may enter the system when the caliper pistons are retracted. Air compresses and increases pedal travel.
• If the vehicle has adjustable wheel bearings, a loose bearing adjustment can cause rotor movement, pushing the caliper pistons in and increased pedal travel
• A caliper piston sticking in its bore after being pushed in. This is particularly common on phenolic and double piston calipers.

Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

1. Pump the brake pedal several times, without the engine running. This will exhaust the vacuum reserve in the chamber. Depress the brake pedal and start the engine. As vacuum charges the chamber, the pedal should drop slightly. This verifies the booster is working and receiving vacuum.
2. Run the engine to charge the vacuum chamber. With the engine off, slowly push and release the pedal, four times, about once every 5 seconds. On each stroke the pedal should rise slightly. This shows the release valve is operating.
3. Run the engine for one minute. With the engine off, hold normal pressure on the pedal for thirty seconds. The pedal should not rise in this time. This test shows if the booster holds vacuum.

• Using contaminated brake fluid. Fluid from a container that has been opened may induce more moisture into the system than is being removed.
• Allowing dirt to enter the system. Hydraulics should be kept as near sterile as possible. Poor service procedures can introduce debris.
• Introducing air into the system. By using poor methods or an improper bleeding sequence, air may enter the system.
• Over-stroking the master cylinder. An older master cylinder can be ruined by pushing the pedal to the floor, as in improper brake bleeding. Corrosion may occur beyond the area of normal piston travel. Pushing the piston beyond this point can ruin the seal. Proper bleeding always limits pedal stroke to the normal area of travel.

• Leaking brake fluid, from the caliper area
• A pull to the right or left on braking
• Rapid brake pad wear and uneven brake pad wear
• Brake rotors that continue to warp
• A wheel that is difficult to rotate
• Heat or smoke coming from the brake with the bad caliper
• A bad shaking in the steering or a feeling the brakes are still applied when driving

Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

• The amount of material remaining on the faces can be too thin. This is checked with a micrometer and there is a published specification.
• The surface finish can be too rough, 60 micro inches is normally considered maximum.
• The faces can be out of parallel. The specification is normally in ten-thousands of an inch.
• The faces can have lateral run-out, normally referred to as warp.
• Excessive corrosion to the faces or structure can make a rotor unusable.
• Cracks in the faces or structure can make a rotor unusable.
• Rotors can also be excessively out of balance, have damaged or mis-drilled lug holes, damaged bearing surfaces, hot spots in the surface and several other flaws.


Any of these things and more can render a rotor unusable. With the importance of the part and the possible consequences of failure, when in doubt, replace.

For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• In your opinion how often should I replace my brake fluid?
  
  Most brake fluid is made of alcohol and absorbs moisture from the atmosphere. This occurs 24 hours a day and whether the vehicle is driven or not. Time is a better indicator of when to change than miles.
  
  Color is NOT a reliable indicator of moisture content. Some fluids that are clear may be contaminated and others that are dark may be okay. Moisture content will lower the boiling point of the fluid and increase corrosion to the system.
  
  Brake fluid can be tested with a refractometer, to reveal its moisture content. Without such an instrument a good rule of thumb would be every two to three years and before any brake service.
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• Is there a difference in changing the brakes on an ABS equipped vehicle and a non-ABS vehicle?
  
  If proper procedures are used there is very little difference. ABS systems can contain several expensive components, such as hydraulic control modules. Pushing the caliper pistons into their bores, without expelling the fluid, can cause problems. Doing so is bad procedure even on non-ABS vehicles. The debris in the caliper can be forced back through the system. Completely flushing old fluid from the system before beginning is the best practice. At least, the bleeder screw should be opened to expel the old fluid.
  
  If hydraulic components are replaced or if air enters the system, some ABS vehicles can be difficult to bleed and require special equipment.
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• My 2002 GMC Yukon ABS light came on, around the same time I started hearing a buzzing noise. When I turned the truck off the noise continued and will not stop?
  
  The electronic brake control module (EBCM) on the Silverado, Suburban, Yukon, Sierra, etc. often causes this problem when it fails. The silicon controlled rectifier (SCR) that controls the ABS pump fails, directing current to the pump continuously. Temporarily removing the ABS fuse, under the hood will stop the pump until the vehicle can be repaired.
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• My ABS and traction control lights come on, what could be the cause?
  
  ABS and traction control are closely related and use much of the same circuitry [see this section on “How does ABS work,” and “How does traction control work.”] When a fault is encountered in a component shared by both systems, both lights will come on.
  
  There could be dozens of causes, some minor and others more major. To diagnose the problem a scan tool is used to retrieve fault codes from the brake control module (BCM). These codes will indicate a general area that could be causing the problem. For instance it could read left front speed sensor fault. At this point the technician uses other equipment to test the components in that circuit.
  
  A great deal of money is wasted by people who take fault codes literally. In the above example, they may simply replace the sensor, only to find the light is still on. The code indicates only what the computer interprets. The cause could be a loose or broken connection, a bad tone wheel, a defective computer driver circuit, a bad tire or many other things. This is why it is much less expensive to refer such problems to trained professionals with knowledge of the system.
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• My brake pedal has become very hard to press lately. I suspect the vacuum brake booster is going out, is there an easy test?
  
  As a quick test, without the engine running pump the brake pedal several times. Now place your foot on the brake pedal with a firm pressure. Start the engine and the pedal should drop slightly. If not the booster is likely not working, but not necessarily bad. The vacuum source to the booster must also be tested with a vacuum gauge.
  
  The gauge should be connected inline with the booster and should read very near engine vacuum with the pedal applied or released. If not, isolate the source of the vacuum problem before proceeding with the booster check.
  
  For more information, please see our Detailed Topic Vacuum Brake Boosters.
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• My brakes squeal when I apply them, after getting a brake job. Is there a break in period?
  
  Modern brakes do not require breaking in and should not squeal objectionably. Squealing on application is always a result of vibration. The pads vibrate on the rotor surface and the noise is transferred through the calipers and into the vehicle.
  
  Stopping brake squeal starts with doing a proper job. Pads, rotors, calipers and caliper slides must all be clean. The back of the pads must be lubricated with high temperature caliper lube. If the vehicle uses pad shims (most do) they must be present and in good condition. All hardware must be present and installed properly. My experience is also that original equipment brake pads make much less noise and stop better than aftermarket pads.
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• My car has a shimmy or shudder when braking. I have been told the brake rotors are warped. Will replacing the rotors stop the shimmy?
  
  Replacing the rotors will very likely stop the shimmy, for a while. Brake shudder is a symptom of a problem, not the problem itself. Replacing the rotors is treating the symptom, but if the root cause is not addressed the problem will return. The possible causes are numerous and can be involved to diagnose. Some of the more common causes are rotors/drums that have been improperly machined. Caliper slides that are binding, improper brake material being used and rear brakes not functioning properly.
  
  For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• My GM vehicle recently developed a high pitched squeal whenever it is rolling. The noise stops when I apply the brakes are sit at a stop.
  
  One strong possibility is the warning indicators on the brake pads rubbing on the brake rotors. This is a warning that the brake pads are worn and will soon begin damaging the brake rotors. The brakes should be inspected and the pads replaced immediately to prevent damage.
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• My rear brakes wear out before the front brakes. What could cause this?
  
  As a general rule, front brakes traditionally wore out before the rear. As with any general rule this is sometimes not the case. For instance the GM Silverado series trucks, with four wheel disc brakes. On these vehicles, rear pads tend to wear faster than the front. Several other vehicles do the same. The size of the pad material and the bias of braking also contribute to wear rates.
  
  If the wear is excessive or rapid, binding rear calipers, master cylinder adjustment and ABS control valve problems can all cause rear brake wear. With drum type brakes, a defective self adjustment system or sticking rear wheel cylinders can also cause rapid rear wear.
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• My steering wheel sometimes shakes in my hands when I apply the brakes. This started about two months after I replaced my front brake pads.
  
  If the shake or shudder is only when you brake, a common cause is warped brake rotors and/or drums. This feels similar to “shimmy” except that it stops when you release the brakes.
  
  To correct shudder caused by rotors and brake drums it is important to remember the warped parts are a symptom and not the root cause of the problem. Merely replacing the rotors/drums will normally only offer temporary relief from the symptom, and it will often return.
  
  The possible causes are numerous and can be involved to diagnose. Some of the more common causes are rotors/drums that have been improperly machined. Caliper slides that are binding, improper brake material being used and rear brakes not functioning properly.
  
  For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• My vehicle has 40,000 miles and the brakes have never been replaced. Is there an indicator that will let me know when they need replacing?
  
  Some vehicles have no indication at all while others have warning lights or an audible warning. It is always wise to inspect your brakes at around 15,000 miles and then once a year thereafter.
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• My vehicle has a shudder on braking and I am told the brake rotors are the cause. The brake pads are still good, is it okay to just replace the rotors?
  
  Brake pads and rotors work together and should always be replaced together. The exception being the brake pads can be replaced without rotors if the rotors are still serviceable.
  
  For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• My vehicle is equipped with an anti-lock braking system but it does not seem to stop any faster than my older vehicle without ABS. Should I have the system checked?
  
  Anti-lock braking systems (ABS) are not designed to make a vehicle stop faster. Their function is to prevent wheel lockup during braking. This helps the driver maintain control of the vehicle as rolling wheels are easier to control than sliding wheels.
  
  The system is designed to test itself when the vehicle is started and at preset intervals when driving. If a malfunction is encountered the ABS light will illuminate.
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• My vehicle pulls to the right when I apply the brake and stops when they are released. I have replaced the brake calipers, rotors, pads and had the suspension completely checked and the wheel alignment set, any ideas?
  
  A very common cause of brake pull is a bad brake hose. Internal failure can cause the hose to act as a valve, blocking brake pressure. Ironically, the vehicle will pull toward the good brake hose as that wheel is trying to stop and the other is not.
  
  See our Detailed Topic article Brake Hoses Can Bury You for far more details on brake hoses.
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• On hard application my rear brakes sometimes lock up?
  
  Rear brake lock up can result from contamination on brake shoes. Most often this comes from a leaking wheel cylinder or a leaking axle seal. Other causes include, a rear wheel cylinder that binds, loose brake components and worn backing plates.

  For more information on drum brakes, please see our Detailed Topic, Solving Drum Brake Problems.

  
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• One brake rotor on my vehicle was damaged by a bad brake caliper. The mechanic wants to replace both front rotors and said damage can occur if not.
  
  Sometimes, when a new rotor is used with an older brake rotor, the vehicle will pull when the brakes are applied. Unfortunately, this may not be learned until the vehicle is fully assembled and driven. At that point the cost is much more to disassemble the vehicle and replace the other rotor.
  
  Beyond a pull on braking I see no damage being done, if the existing rotor is in serviceable condition. You might check the price both ways and then weigh the risk. If you inform the shop, you are willing to assume the risk, they may be more willing to try.
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• Power steering fluid was accidentally added to my brake fluid reservoir. Soon after, the brake warning light came on.
  
  Rubber seals used in brake systems are designed to work with alcohol based fluid. Petroleum based fluid, like power steering fluid, will quickly destroy the rubber parts of the system. Since failure of almost any seal in the brake system is critical, replacing every rubber component in the system is the normal repair. It is also necessary to clean thoroughly all other components such as the steel lines. Any traces of remaining contaminants may cause future problems.

  Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

  
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• The first brakes on my Toyota lasted 40,000 miles. I had them replaced 15,000 miles ago and now the left front is metal on metal on the outboard pad, and has ruined the rotor. The shop says it must have been a bad set of pads and suggest new
  
  You are wise to be suspicious. Replacing only the pads and rotors seems like treating the symptom only. Each brake caliper on your vehicle has one piston and two pads. This means the piston applies the inboard pad and the outboard pad is applied by the caliper bracket moving on the caliper slides. If these slides are not free to move they will apply the outboard pad, but not release it. This will cause very rapid wear to the outboard pad.
  
  The caliper slides should be inspected and serviced or replaced as needed. Improperly serviced caliper slides are a source of a great many problems. Proper service of the caliper slides should be part of every brake service.
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• The front brakes on my vehicle are getting thin and I plan to replace the pads myself. Do you recommend turning the brake rotors?
  
  I only recommend turning rotors under very few conditions. If the vehicle stops smoothly and with no vibration or shudder, the rotors should be inspected. If the thickness measures within specifications and the surface has no groove beyond .050 inch deep the rotors can be reused. The surface should be thoroughly scrubbed with hot soapy water before use.
  
  If the rotors are worn below specifications they should be replaced and not reused. If the rotors are warped, it has been my experience that it is also best to replace them.
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• The front wheel bearings in my truck needed to be replaced. The shop recommended that I also replace my front brake pads, even though they were not worn out. Is this a good idea?
  
  It could be, you need more information. Brake pads might be suggested for several reasons, other than just wear. When the front bearings are removed the brake pads are very accessible. If they are getting thin, even though not worn out, it may be far less expensive to replace them now.
  
  Weighing the remaining amount of brake against the cost savings might give you a better idea. For instance, check the cost to replace them now as opposed to replacing them later. The saving could then be compared with the remaining life expected from the present brakes. It should also be asked if there is another reason they are being recommended. For instance, has grease from the bearing seal gotten on the pads or are the pads otherwise damaged.
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• The rear axle seal leaked oil onto my brake shoes. The shoes are good other than that can they be cleaned?
  
  Brake shoes cannot be cleaned of oil. The oil permeates the material and will continue to secrete out when the shoe reaches temperature. Any cleaner that might be used can also break down the brake material, causing them to deteriorate. The shoes should be replaced and the drums very thoroughly cleaned to remove all traces of oil.
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• There is a deep scratch in one of my front brake rotors. What should I check for? Does this indicate a bad brake caliper?
  
  I would check to see if the brake pad wear is even from side to side and inboard to outboard. If wear is even and there is no signs of overheating (blue color to the rotor,) a brake caliper is not likely. You can also check the force required to rotate both front wheels. A sticking brake caliper will usually produce a noticeable drag in the rotating wheel.
  
  Scratches sometimes result from debris trapped between the pad and brake rotor. With no other symptom, I would not be overly alarmed by the scratch alone.
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• What are the symptoms of a bad brake caliper?
  
  The symptoms can vary greatly, depending on the type failure experienced. For instance, some calipers may leak, but cause no additional problem. The only symptom might be a low fluid level. Another may seize in the open position. This will often result in a pull on braking, ironically in the direction of the working caliper.
  
  It is also possible for calipers to seize in the closed position. This normally results in overheating the rotor. Symptoms can be a burning smell, smoke, vibration, noise and a good deal of dusting. In less severe cases, there are often no noticeable symptoms when driving. In these cases an inspection of the brakes will sometimes show a brake pad worn significantly more than the others. Sticking calipers also often result in warped rotors, and shudder when braking.
  
  For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• What are the symptoms of a bad brake hose?
  
  Brake hoses can fail in a number of ways. They can leak or rupture, this causes the brake pedal to fall drastically and diminishes braking. They can break down internally and cause a pull to one side or the other on brake application. One of the most common symptoms and one that is often overlooked is a bad brake caliper. Debris from failing brake hoses is a leading cause of brake caliper failure, in our experience.
  
  For more information on brake hoses, see our Detailed Topic Brake Hoses Can Bury You.
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• What are the symptoms of a bad vacuum brake booster?
  
  There are at least four primary symptoms and they may occur in combination.
  1. The brake pedal may be harder than normal to depress.
  2. There may be a noise, often a hissing or squeak when the brake pedal is depressed.
  3. The brake pedal may not return to the proper height when released.
  4. The brake pedal may kick-back are jerk when pressed.
  Always test for a proper source of vacuum and rule out conventional brake problems before condemning the brake booster.
  
  For more information, please see our Detailed Topic Vacuum Brake Boosters.
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• What are the symptoms of a leaking brake wheel cylinder?
  
  The symptoms will vary, based on the severity of the problem. With minor leakage, where the fluid is contained within the dust boot of the cylinder, the only symptom may be a slight loss of fluid in the master cylinder. As the condition gets worse, fluid can leak onto the brake linings. This can produce a grabbing or locking of the brakes on application. As the brake material becomes more saturated, we lose friction and the affected brake will not stop the vehicle. This often causes the remaining brakes to work harder, sometimes resulting in noise and/or a shudder on stopping.
  
  If the cylinder leaks enough fluid, we may lose the hydraulic action of the system. This can result in severely diminished stopping or possibly a loss of brakes.

  Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

  
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• What are the symptoms of air getting into brake lines?
  
  Since air is compressible, the major symptom is always a low or soft brake pedal. That is, when the pedal is pressed, it travels farther and does not get firm until near the end of its travel. Hydraulic pressure in the brake line compresses the air and this acts like a spring causing the soft pedal. The process of removing air from the brake line is called bleeding. There are several methods of bleeding brakes, depending on the system. There is normally also a specific sequence in which the wheels are bled, depending on the vehicle.
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• What is automatic traction control?
  
  Design varies from one vehicle to another and operates similar to anti-lock braking systems (ABS). In fact many of the same components are used. Sensors read the speed of the drive wheels. This information is fed back to a computer that compares these wheels to the others. When a drive wheel increases speed to a predetermined percentage above the others, it is inferred to be spinning. At this point depending on the system, braking may be applied. Sometimes engine power is also reduced. Some systems may direct torque to the non-spinning wheel.
  
  When the spinning wheel slows to equals the other wheels, the system ends control and continues to monitor wheel speed. This may occur many times per second and switches among wheels as needed. Certainly this is a vast over-simplification but is the basic concept.
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• What is DOT 5 brake fluid?
  
  DOT 5 is a silicon based fluid, unlike DOT 3 and DOT 4 which are alcohol based. It is incompatible with and should never be mixed with alcohol based fluids. The advantage to DOT 5 is that it does not become contaminated with moisture like DOT 3 or DOT 4. DOT 5 is primarily used in restored older vehicles which do not have anti-lock braking systems (ABS).
  
  The rapid motion of the ABS components can cause DOT 5 to become aerated causing us to lose our brakes. Therefore DOT5 is not used in vehicles with ABS. Converting a vehicle from DOT 3 or DOT 4, to DOT 5, should always include replacement of every rubber component and thorough cleaning of all metal parts.
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• What is meant by discard measurement on brake rotors?
  
  Brake rotors are designed with a specific thickness in mind. This is important, not only for strength and heat dissipation, but to assure the calipers are not over extended when the pads wear out. The discard reading is the thickness below which the rotors should no longer be put into service.
  
  There is also a machine to limit, which is thicker than discard. This is the minimum the rotors can be safely machined to. It takes into account the amount the rotors will wear in the life of the pads.
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• What is the advantage of disk brakes over drum brakes?
  
  With a disk brake, there is no drum to retain water. This makes them more resistant to fade when driving though water. The spinning disk also tends to dissipate heat better than a brake drum. There are also fewer moving parts and disk brakes are inherently self adjusting.
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• What is the best brake pad for my vehicle?
  
  The brake pads originally designed for the vehicle, by the vehicle manufacturer have proven to us to give far superior service than aftermarket replacements. Rather than one material fits all, original brake pads are designed specifically for the vehicle. We have found they produce less noise, less dust, stop better and do not contribute to warping of brake rotors.
  
  It is also very important to realize that not all brake pads sold or installed by dealerships are original equipment manufacturer [O.E.M.] pads. For instance Dura Stop and Motorcraft pads sold by GM and Ford dealers are aftermarket products. Be certain to ask for and insist on original equipment manufacturer [O.E.M.] brake pads.
  
  For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• What is the difference in a primary and secondary brake shoe?
  
  With duo-servo brakes, the primary brake shoe is the one that contacts the brake drum first. This causes both shoes to rotate slightly, with the brake drum, and forces the secondary shoe into tighter contact. The primary shoe is often in the front position and most of the time is slightly smaller than the secondary.

  For more information on drum brakes, please see our Detailed Topic, Solving Drum Brake Problems.

  
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• What is the difference in DOT 3 and DOT 4 brake fluids?
  
  DOT 3 and 4 are both alcohol based fluids and are compatible with each other. DOT 4 has a higher initial boil point than DOT 3, when both are fresh and uncontaminated. Because of the agents that give DOT 4 a higher boil point, it is also more susceptible to contamination. Moisture can enter the fluid and lower the boil point significantly. For this reason, DOT 4 should be replaced more frequently than DOT 3.
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• What is your opinion of the brake fluid test strips? They claim to detect copper in the fluid as a means of testing the corrosive potential of the fluid.
  
  The test strips work well and we use them in addition to refractive testing for moisture content. A possible draw back is they tend to detect corrosion that is already occurring. They are useful for folks that do not have records and need to know where they stand. An example is with a used vehicle inspection. Where possible, I find a better approach is to be proactive and replace the fluid about every two to three years. I feel this more likely preempts the corrosion issue.
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• When bleeding brakes, should I always start at the wheel furthest from the master cylinder?
  
  At one time that procedure was common. It can no longer be universally applied as many vehicles specify different bleeding patterns. Some vehicles use cross braking, with the left front wheel connected to the right rear. The right front is also connected to the left rear. It is not uncommon to see left or right front wheels bled first. From there some bleed the other front and others an opposite rear and so on. Most good shops refer to service data for the vehicle being worked on to be certain the right procedure is used.

  Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

  
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• When I flush the brakes on my Chevrolet Impalla, how much fluid will I need and is one fluid better than another?
  
  Your Chevrolet specifies Dot 3 and will require about one quart to flush the system. Fluids labeled Dot 3 and Dot 4 are similar in chemical makeup. Dot 4 has a higher dry boil point but will become contaminated faster than Dot3. I always recommend putting back what the vehicle manufacturer specifies.
  
  Never buy more fluid than is required and dispose of any left over fluid. Dot 3 and 4 are very hygroscopic and will become contaminated in time, even in a resealed container. Even with the volume of brake fluid we use in the shop, we buy in quart containers. This helps ensure a fresh fill in each vehicle.
  
  My test have shown brake fluid in metal cans and with a metal seal at the neck, to be dryer than the plastic bottles. I would also suggest buying a major brand, from a supplier that does a high volume of business.
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• When I try to bleed my brakes the pedal keeps getting lower. What am I doing wrong?
  
  There are several methods of bleeding brakes, depending on the design of the brake system. Using the improper method will result in the pedal dropping and possible damage to the system.
  
  The means of applying pressure and the order in which the bleeder ports are opened varies considerably. The order is known as bleeding sequence and varies considerably from model to model. On older vehicles bleeding normally started at the wheel furthest from the brake master cylinder. With modern brakes there are several patterns. Using the wrong sequence can result in even more air being drawn into the system.
  
  Older systems also normally recommended pumping the brake pedal to produce pressure in the system. This will no longer work with many systems and can cause damage to the master cylinder. Instead, combinations of pressure tanks, vacuum and reverse pressure are often used. Many newer systems must have a factory scan tool to run the ABS pump in order to bleed air from the system. You will need to refer to the service data for your vehicle to determine the proper bleeding method and sequence.
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• When should brake calipers be replaced?
  
  We find that brake caliper life is influenced greatly by three main factors.
  
  1. The original design of the part. For instance, phenolic piston calipers are more susceptible to problems than metal piston types.
  2. The care they have received. For example keeping brake fluid fresh can extend caliper life. Driving in areas that heavily salt roads tend to create problems. Damaging the protective boots during other service will shorten life.
  3. Time; Age seems to be more of a factor than mileage.
  
  Calipers normally fail, either by leaking or by seizing. Leaks are fairly obvious and loss of brake fluid is a symptom. Some of the symptoms of a stuck caliper may be warped rotors, over heated brakes, pulling one way or the other on braking and uneven brake pad wear.
  
  For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• When should brakes be replaced?
  
  That is an interesting question, with several answers. The short answer might be when they cause a problem objectionable to the driver or present a safety concern. Obviously when the brake pads wear out and begin damaging the rotors and drums they should be replaced. This is when the characteristic squeal or growl is heard. There are also times when people replace their brakes even though they are not worn out:
  
  
  
  
  • To address a noise concern, even though the pads may not be worn out
  
  
  
  • To correct a shudder or shimmy that occurs when braking
  
  
  
  • When a wheel cylinder leaks and the shoes are damaged
  
  
  
  • When other work in the area substantially lowers the cost of replacement at that time
  
  
  
  • To increase brake performance, even though the pads are not worn out
  
  
  
  • To avoid a future problem or for convenience
  
  
  
  
  The only true way to determine the condition of the brakes are with a physical inspection. Some wear out in as little as 20,000 miles and other go well over 150,000 without replacement. The design of the brakes and driving style are the two largest factors.
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• When should I flush my brake fluid?
  
  Testing brake fluid is somewhat difficult, but can be done with a refractometer or some types of test strips. In the absence of such devices two to three years is a good rule of thumb. Brake fluid should also be flushed BEFORE replacing any hydraulic component in the brake system. A search on the key words BRAKE FLUID on this site will also provide a good deal more information.
  
  
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• Which should last longer, rotors or brake pads?
  
  The answer depends largely on three factors. First the nature of the design. Many European vehicles wear out a set of rotors as quickly as the brake pads. Domestic and Asian vehicles normally will wear brake pads quicker. The second factor is the type of brake pad used. Harder pads wear rotors more quickly. Last is driving style. With aggressive braking, a set of rotors can be worn/warped quickly, regardless of the design. With easier/lighter braking and a proper set of brake pads, a set of rotors may last the life of the vehicle in many instances.
  
  For more information, please see our Detailed Topic Brake Shudder, Calipers and Noise.
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• Why do brakes need to be bled?
  
  Brakes use hydraulic force to apply the components. When the brake pedal is depressed, brake fluid pressure is tremendously increased. This pressure is what moves the pistons in the brake calipers, wheel cylinders and applies the brakes. Air can be compressed and acts like a spring. When pressure rises, the air is compressed rather than applying the brakes. This causes the pedal to sink and braking is diminished. This is often called a spongy brake pedal.
  
  Bleeding the brake system removes air that enters when the system is opened. Since the system remains sealed, fluid pressure will keep air from entering again.

  Please also see Basic Hydraulic Brake Diagnosis and Repair for far more detail.

  
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