Introduction: Disk Brake Repair
Everyone focuses on cars that go fast. No matter how fast your car goes, it eventually has to stop. Whether your car is 40 years old or 4 years old, you're going to face the prospect of brake failure sooner than later. Regular maintenance can help avoid a very bad day.
I called around my area to get quotes on brake jobs. The cheapest quote I got was $150 per axle, $300 per car. And that's the low end. The mechanic on that quote told me that if there were any other issues other than standard brake wear, it went up to $200/axle. The highest bid? $300/axle, $600/car. And that's for a standard passenger vehicle. If you have something exotic... well, if you have something exotic, you can afford to pay someone to fix your brakes, and you wouldn't be here.
If you have a smaller economy car, or your car is older, then you may have drum brakes in the rear. Why the two systems? Disc brakes deliver better stopping performance overall, but tend to have a shorter life than drum brakes. Drum brakes can take more abuse than disc brakes. So they put discs up front, drums in the rear. At least that used to be true - modern braking systems are making drum brakes mostly obsolete.
In this Instructible, I'm going to cover how to overhaul disc brakes. Disc brakes are on the front of 99% of passenger cars sold today. Doing this work yourself will save you tons of money. This video will include shots of my 2006 Hyundai Sonata and my 1992 Nissan D21. The day I did this repair, I overhauled front and rear brakes on both vehicles - up to $1,000 in parts and labor - for just $211.
Step 1: Gather Repair Parts
Before we dive in, let's discuss driving style and whether you need high performance pads and rotors.
I know what you're thinking: "Why not just get the highest performance stuff I can? FTW!" Not so fast - brake pads and rotors are designed to work in a narrow range of operating conditions. The daily driver who commutes just a few miles each day is far less demanding on their braking system than the average mini-van driving soccer mom with the "Mom's Taxi" license plate frame. And the Road Warrior who commutes into the city on a six lane death-strip of a freeway is right behind the guy who takes his sports car to the track on weekends to race it. If you put racing pads on a Daily Driver, you'll find that the stopping performance is worse than the typical budget brake pads. Maybe not as bad as the Road Warrior who puts the cheapest pads on his car, then can't figure out why he has stand on the brakes to avoid slamming into the semi-truck at the bottom of the off-ramp.
Match your parts to the driving habits. So if you're a Daily Driver (low demand), Soccer Mom (medium demand), or Road Warrior (street performance), you need to make decisions about what pads and rotors to buy to replace your old ones. Let's start with rotors.
The first question is whether you need to buy rotors at all. 99% of the time, I'm going to say yes, and the reason I say yes is because standard OEM rotors are just so dang cheap! If you look at my bill of materials on the last page, I bought new front rotors for my truck for $12 each. Shipping was only about $7, because despite being heavy, they don't take up a lot of room, and the cost of shipping is mostly in the bulk of a package. If you don't replace your rotors outright, then they'll need to be machined. More on that later. The cost of machining is $10/rotor. Sometimes when a rotor gets machined, too much material has to be taken off. If rotors aren't a certain thickness, they can't handle the heat they'll experience in braking, so they have to be replaced anyway. So if you're talking $15.50/wheel for new rotors, or $10/ wheel with a 50% chance of having to replace them, you might as well just buy new discs.
That's for standard rotors, and standard rotors are just fine for the Daily Driver and the Soccer Mom. But for the road warrior, you're going to want a rotor that's a little higher performance. Enter the vented, drilled and slotted features on rotors. Or combinations of all three. Each feature is designed to do something different:
- Vented Rotors - These rotors are almost universal. It consists of two disks with veins in between them that allow air to flow through the inside of the rotor. It's actually been many years since I've seen a completely solid rotor, so this is almost not worth discussing except to say that the vented rotors actually suck air in at the hub and spin it out the edges as the wheel rotates, allowing them to cool. This only counts when the wheel is turning, though, so if you have a particularly hard stop and then sit on the brake, the rotor is still going to absorb a lot of heat. This is why rotors are generally made of steel - it's a good solid heat sink material.
- Drilled Rotors - This is a simple as it sounds - the manufacturer drills holes into the rotors. The "why" is because when you hit the brakes hard and the pads heat up, they will start to ablate - shed small amounts of material - and will also start to cook, giving of small amounts of hot gas. With no place to go, the gasses and dust form small cushion between the pad and rotor, reducing stopping performance. This is what causes the "fade" when braking hard, in which you have to press even harder to get the same amount of stopping power. By drilling small divots in the surface of the rotor, it creates pockets where the gasses and dust can flow into and break the cushion until the disk rotates out from under the pad. In some cases, the holes are drilled completely through the rotor. This allows the gas to fully escape, and it looks hella cool, but comes at the expense of the mass of the brake rotor, making it not such a good heat sink. The pattern of holes can also lead to uneven heating and cooling, which results in warping of the rotor.
- Slotted Rotors - Slotting solves the same problem as drilling your rotors, looks even more hella cool, but also preserves the heat-sink capacity of your rotors. Because the slots are cut at angles to the pads and wider than your pads, the gasses are able to escape radially. And because the slots are evenly cut, they lead to an even heating and cooling of the rotor. Warping can still occur, but is less likely.
Any combination of these three features will increase performance. If you're a Road Warrior, look for a decent set of slotted rotors, with or without drilling. If you're a Commuter or Soccer Mom, standard vented rotors - which you probably already have - are just fine. Note that slotted rotors are a little nosier, producing a humming noise under braking pressure.
Pads, more so than rotors, have the most direct impact on your stopping performance. But there are also other considerations, like how fast they'll wear out, how much dust they produce, how loud they are, etc. There are three basic types of pad:
- Organic - Organic brake pads (officially "Non-Asbestos Organic", or NAO) pads are made from carbon fiber, glass, rubber, kevlar and other materials that are mixed with a resin and compressed in a mold under extremely high pressures. The result is pad that is inexpensive, soft, quiet, and gentle on your rotors. They don't offer the best stopping performance under hard braking conditions. They tend to wear out quickly, and they create a lot of dust. A lot. If you like a clean car, but don't want to have to wash it weekly, stay away from organic. If you're a cheap skate and a Daily Driver, then these are ideal.
- Semi-Metallic - Semi-metallic pads are called sem-metallic because they're about 1/3 to 2/3's metal. Think steel wool, copper wire, mixed with binders and pressed in a mold. Semi-metallic pads offer good braking performance under a wide range of conditions. Road warriors who don't want the cost of a ceramic pad can opt for semi-metallic. Soccer Moms and Daily Drivers who want better performance than an Organic should go to semi-metallic.
- Ceramic - Ceramic brake pads offer the best overall performance. As the name implies, they're made of ceramic - like your dinner plates or bathroom tiles. Ceramic materials can often handle extremely high temperatures and stresses. The belly of the space shuttle was lined with ceramic tiles to survive re-entry. Ceramic brake pads are easier on your rotors. Ceramic does tend to be pricier, often double the price of organics. They also tend to not work as well when they're cold. If you're a road warrior, you'll want to go with ceramic. If you're a commuter or soccer mom, you will want to stay with semi-metallic. In both cases, avoid the high performance labelled pads, and get street performance or just street. High performance pads are designed for heavy braking conditions common on tracks, but don't work well until they get hot.
A word about asbestos: Asbestos is great stuff. It is a great electrical insulator, can handle stupid high temperatures, and naturally occurs in nature. At one point, asbestos was used in everything from brake pads to siding on houses, to insulation around pipes in commercial and industrial settings as well as homes in extreme cold climates. Then someone figured out that inhaled asbestos can cause cancer, mesothelioma, and annoying commercials by big law firms. The automotive industry phased asbestos out during the 1980's for all but a few specific high-performance applications. By 1995, you couldn't find asbestos brake pads if you wanted to. But despite this, people will tell you to avoid working on brakes because of the danger of asbestos fibers. In the unlikely event that you're going to be working on a care from the 1990's or earlier which has not had a brakejob in the last two decades... hey, it could happen... all you have to do to avoid this problem to use a chemical called "dihydrogen monoxide" with a small amount of surfactant. For the lay person, I'm talking about "soapy water". Wash it off, and wash it away. The danger of asbestos is in inhaling it in concentrated form in an occupational setting. Frankly, organic, ceramic and metallic brake dusts aren't much better for your lungs, so before you do any brake job, either wash your wheels or wear a dust mask.
Step 2: Disassembly and Inspection
Now we get to the fun part - wrenching... your wrists. And busting your knuckles. All projects require a sacrifice in blood. But I do recommend you avoid it where possible. Start by putting on a good pair of work gloves. These can be as little as $4 at your local home improvement store, and there's no excuse to not have a pair. Because I work in an office environment, I like to also wear some latex gloves at the same time. This helps me avoid the 20 minutes of scrubbing my hands raw so that I don't have dirty hands when I hand in my TPS reports to Bill Lumberg.
You're going to need to jack your car up and take the wheel off. I have another Instructable on how to jack your car up and take the wheel off. Isn't that convenient?
Take the Caliper Off
With the car in the air, you'll need to remove the bolts holding the caliper. These are usually on the back-side of your caliper. One problem you'll often have is that the caliper is usually a free-floating caliper where the bolts actually go into a set of sliding pins in the caliper assembly. You'll need to use a wrench to hold these pins in place while you work the bolts loose. If all else fails and you find that even a wrench will not fit onto the pins, then go ahead and use a pair of pliers, but try to avoid this since it will superficially damage the pins.
Once you do that, you can work the caliper off. It's a good idea to have some coat-hanger wire nearby to hang the caliper from the suspension. The alternative is that you can balance the caliper on the suspension. This is a dangerous idea, since the caliper can fall off. Why is that bad? Your caliber is still connected via a brake line, and when the heavy caliper reaches the end of that line, it could damage or break the brake line. That's a bad day, because not only do you have to repair the brake line, but you have to now bleed the braking system to get rid of the air that got it. Don't let the brake caliper just dangle from the line, either. Again, the stress will damage or break the brake line.
Do not break to your brakes.
Take the Carrier Off
The thingamabobber that your brake caliper was bolted to is called the carrier. This is for obvious reasons - it carries the caliper. It also holds the brake pads in with the help of some spring clips. It also attaches to the spindle and takes all the force of stopping your car. It's also in the way of you taking you rotor off. And chances are good that the brake pads are still in there, so first pop those out. But make a careful mental note of how the pads are inserted into the carrier, and how the spring clips are inserted as well. Now is a good time to break out your phone and take a picture.
The carrier is held in place - typically - with two bolts on the back side of the brake assembly. It will often take quite a bit of force to get these loosened up. A breaker bar is your friend. Also, because you're working backwards, try to remember that it's now right-loosey, lefty-tighty. I'll admit to my fair share of trying to tighten a bolt that I wanted to actually take off because I was approaching it from the opposite direction.
Take the Rotor Off
For many cars, the rotor should just slide off at this point. But for some cars, there are retainer screws that hold the rotor in place. They may be phillips head, or they might be hex head. Almost all of them will be a complete pain to remove. The combination of harsh elements and high heat in the rotor will cause them to be tightly bonded in place. If you can't break it free with a screwdriver, then use a drill driver so that you don't strip the head. But if your drill driver can't loose in up quickly, then you'll need to punch that thing.
By which I don't mean with your fists. You need a tool called a "pin punch", which is just a rod of metal that you strike with a hammer on one end. If you don't have one, then do what I do: misuse a tool. In this case, I have a socket extension, which is made from hardened steel and will do the job. By placing the end of the punch on the screw head, then giving a few sharp whacks with a hammer, you can usually crack loose a seized bold or screw without damaging it.
With the retaining screws out, the rotor should come off.
Having taken your brake assembly apart, now is a good time to inspect everything in and around it. Here are some common things you can do while you're in there:
- Brake Lines: Look for cracks in the outer lining. This doesn't mean your brake line is bad, but the outer lining protects a layer of either steel or kevlar braiding that surrounds the inner lining. With that protection gone, you should make plans to replace that line ASAP.
- Wheel Speed Sensor Wire: Your wheel speed sensor senses wheel speed. Why is this important? Because your traction control and anti-lock brakes need this information from all four wheels to do their job. Losing just one sensor may mean your system doesn't work at all. If there are any signs of damage to the insulation (cracking, slices, etc), then plan to replace it ASAP.
- Wheel Bearing: A visual inspection of the nut and washer around your wheel bearing is usually sufficient. If it looks like it's "bleeding", that means there's rust inside the wheel bearing, which means the grease packing wasn't sufficient to prevent water from penetrating. Without sufficient lubrication, the bearing will fail. Spin the hub (the round thingy the rotor was bolted to). If it spins evenly, that is a good sign. If you feel it "catch", and is harder to turn in some spots, then that indicates a failed bearing. Another big clue is if you hear crunching noises. That shouldn't happen. Lastly, if you grab the hub and you can shake it or make it wobble, that also indicates that the bearing is worn out. The good news is that replacing bearings is often stupid easy to do, and pretty cheap.(I have an Instructable coming on that too.)
- The CV Boot: The "Constant Velocity" joint is the part of the axle that turns at an angle to the other part. CV joints allow your suspension to move freely while the engine drives the wheels. You can't actually see the CV joint because it's covered in a round, accordion-like thing called a "boot". These boots are made from rubber, and protect the joint itself from debris getting in and grinding the joint out. They also hold in the axle grease that keeps the joint lubricated. As they get old, they tend to split inside the folds. Visually, you can see the split because grease will leak out. But to be absolutely sure, you should feel around with your finger and poke at it. If your finger goes in, that will tell you that failure of the boot was about to happen anyway. The good news is that replacing the boot is cheap - far cheaper than the entire CV half shaft.
- Tie Rod Ends: The tie-rod ends are at the ends of the tie rods. I know... seems too easy. Their job is to connect to the spindle and transmit steering forces from the rack to the wheel. They are easily the hardest working parts of the suspension, because every time you move the wheel just a little, they move. Now you can't tell from this position if the tie rod ends need replacing. What you're inspecting is the rubber seal that holds the grease in to the joint. If you see grease, or you see cracks in the rubber seal, the tie rod end is at risk of having water and debris penetrate the joint and cause failure. In the old days, you would just replace the boot and inject some grease. Nowadays, you replace the whole joint prior to failure. When you do the car will likely need a front end alignment. If your tie-rod ends aren't showing signs of slop (which you can feel in the steering wheel when you turn), then you can probably wait until the next time you replace your tires and kill two birds with one... tie rod end.
Once your done with inspections, you can decide if you need to go get more parts, or if you're ready to put it all back together.
Step 3: Repair & Replace
First, go back to the step where I explained what rotors do. Because the only reason you should be getting your rotors turned is if you're a Road Warrior who bought high performance slotted and drilled rotors. Otherwise, it is typically NOT cost effective to have them turned.
That being said, turning your rotors is a step that cannot be skipped. If you look at the pictures above, you'll see my rotor before and after turning. These rotors are now six years old, and they have put up with some intense freeway driving. The ripples you see on the surface will happen eventually to any rotor. What you can't see is the very slight warping in the rotor. Magnified, the disc of the rotor would resemble a saddle shape. This occurs because of uneven heating and cooling of the rotor over time, and leads to a "pulsing" sensation in the puddle. The warping and the ripples together dramatically reduce your overall braking performance because it reduces the amount of contact taking place between your pads and the disc of the rotor. If all you do is swap pads, this will be even worse - you have the flat pad surface that is riding on the tops of the ripples at the same time it skips over the hips of the saddle.
When you take your sport rotors to a local mechanics shop, what they'll do is put it on a lathe, and a mechanism will slowly cut along the surface of the disc shaving off material.(Watch this video to get an idea.) If you have a shop that doesn't often see sport rotors, they may be reticent (big word) to machine them. There's a pervasive myth that these kind of rotors can't be turned. The reason for that is that most mechanics will try to turn them like a standard rotor - with a deep cut on one pass. Instead, they'll need to take 2-3 shallow cuts for a rotor like this. The result is the second picture - a beautifully machined and flat surface that will maximize contact between the rotor and pads, and deliver the best possible braking performance.
(PS: I was quoted $10. Frankly, I think a shop should charge more like $15 for the extra time it takes to cut the rotors. But I still paid $10.)
Those Pesky Screws
Remember those retaining screws that were so hard to get off? Save yourself some trouble on your next brake job - pick up a tube of anti-seize lubricant at the automotive store. This is basically a grease with small particles of aluminum (sometimes copper) that helps protect the threads against corrosion, galling and thermocompressive bonding. In plain English, it'll be easier to unscrew them next time.
Assembly is the Reverse of Disassembly
At this point, just put everything back together just like you took it off. Disc brakes are pretty simple with only a few parts. There are only two places where you might run into a hassle.
The first is putting the pads in. There are four distinct pads - and inner left, outer left, inner right, and outer right. Are they labelled? No, that would be simple. The inner pads have a big metal clip on them. These are "squealers", and their job is to make contact with the rotor when the pad is at the end of life. When they contact the rotor, they make a squealing noise. The squealers go to the back side of the rotor. The outside pads look alike, and often times they are exactly alike. The way to tell is to look at the face of the pads. If only one side of the face has a chamfer, then that chamfer is the leading edge of the pad. Think in terms of how the wheel spins, and that part of the pad should be the first part to engage the rotor when braking. If there is a chamber on both sides, then you don't have to worry about it. Just pop your springs into the carrier, and load the pads into the springs.
The second hassle is that your caliper's piston is extended, and needs to be compressed to account for the additional material on the new pads. To do this, you usually need a tool called a "brake tool", or "caliper compressor". They're about $10, and they're basically a screw through a metal plate with a movable jaw on one end and a knob on the other. In a pinch, you can sometimes use a large c-clamp. One tip I recommend is to put a large socket down in the piston, and seat the movable jaw against that. It saves you time, but it also helps distribute the force of the movable jaw over a larger area, which can prevent racking the piston inside of the sleeve and damaging the caliper. The piston should move pretty firmly but surely until it bottoms out. When turning the screw no longer budges the piston, you're done. Before you do any of this, I recommend that you pop the cap off your brake fluid reservoir and wrap a rag around the opening. When you start compressing the piston, it will push fluid back up into the reservoir. When this happens, the lid may just pop off on its own, and you have to go searching for it. If not, the pressure could crack the plastic reservoir. (That's a bad day - you'll need to order that part, or go crawling around a salvage yard.) The rag is to catch any extra fluid that gets pushed out should the reservoir ever have been over-filled. When you're done, put the lid back on and wipe up any excess fluid.
As you assemble the brakes, make sure you do not get any grease or oils on the rotor or the surface of the pads. Think about this - brakes work by friction, so if you allow a lubricant onto the surfaces, you'll basically defeat the purpose. If you do get some on, you can use an typical solvent spray like brake cleaner or starting fluid (ether). Do not use carburetor cleaner, since it contains petroleum distillates that are basically oils.
Step 4: Finish the Job
So you've put everything together, put the car on the ground, and now you're done. Well, no, you're not. First you need to start the car and pump the brake pedal a few times. This is to adjust the caliper position so that they're making good contact with the new pads. After you've done this, check your brake fluid level. If it's not up to the top line add some brake fluid. Note that this is the only time you should add brake fluid. The bottom line indicate the level of fluid you should expect when your pads are just about worn out, and your brake fluid is cold. Unless your brakes are leaking, you should never have to add fluid. And if your brakes are leaking, adding fluid is not fixing your problem.
If you're a Road Warrior, you'll have one more procedure you need to do that the Daily Driver and Soccer Mom don't need to worry about: you need to "bed your pads". Bedding is the process of transferring material from your brake pads onto the rotor. This naturally occurs over time during normal driving. But for a high performance driver, there's a chance that you'll get road dirt and debris bedded in addition to pad material. Having pad material bedded helps improve initial braking performance. It also helps get rid of the "new pad" burning smell right away.
Bedding procedures will vary depending on your pad manufacturer, but they generally work as follows: you drive around your neighborhood, making a series of gentle stops from about 25 mph. Then you work your way up to roadway speeds - 35 to 45 mph - and make 2-3 gentle stops. This will warm up both the pad and rotor for what happens next. From 45 mph, you're going to make 2-3 hard stops. You will follow this up with a hard stop from 55 mph. One thing you'll notice right away is that braking performance improves from the first few stops. You'll also notice a discolored band on your rotor indicating that rotor material has been bedded (and, to a lesser extent, that the metal surface of the rotor has been polished by the pad a little as well). If you're a Daily Driver or Soccer Mom, you can do the bedding procedure or not - it won't affect the overall performance in the short term, and your pads will naturally bed over the first 20 to 30 miles of driving either way.
Now get out there and turn a wrench.