Brake in procedure - for changing pads and/or rotors
04-06-2012, 10:18 PM
#1
Brake in procedure - for changing pads and/or rotors
I would like to outline how to break in new brake pads. There are many ways and theories (as there can be after replacing an engine's piston rings), but if you are a beginner, this is a great way to make sure your brakes last...and don't vibrate the car to hell.
When you get new pads and rotors, the pads and rotors are not going to initally give full braking. This is because the surface does not give full contact. Both surfaces are not completly smooth, they may have bumps and dips that are small fractions of a millimeter that you cannot see. But when they are new and touch for the first stop, its possible that only 10% of the actual pad touches the actual metal of the rotor. So for your first hard stop, the car not stop anywhere near what you'd expect.
diagram 1.
This is a crude picture I know, but this is what most of your brake setups would look like from the side. That piston is going to push the inner pad, and there is a slide pin that allows the caliper to move, and will make the caliper pull on the outer pad too, toward the rotor. Notice that it looks like the pad and rotor are totally smooth, and your brakes to the naked eye will seem that way when they are new.
To remedy this, you want both surfaces to have their small raises and dips compliment each other, increasing surface contact. Remember, disc brakes work by pushing two pads against a spinning disc, and using the friction, slow the disc's rotation thus slowing the car.
diagram 2.
Another crude picture, but if you were to zoom in on the pad and rotor enough, the surfaces would be something like this. See the gaps between them. Becuase the raised parts are so small, and that there will me the same force applied over less area, the pressure will be increased. During the first stop, this will be felt as a quick nose dive in the car. Since these raised parts are so small, they will wear out very fast, which is the purpose of the brake in procedure. You wear out the raised parts of the pad, and as it wears, digs into the rotor, and the lowered parts of the pad will then hit the untouched and now relatively raised part of the rotor. When the brakes are used enough through the brake-in period, you should have the whole pad contact the rotor like in the first picture.
diagram 3.
When the pads will break in and the car is then driven most of the pad's life, it will look something like this. You will see they are still uneven. A flat contact surface would net 100% the surface area of the pad. Since there are these raised and lower parts, its as if there are mountain ranges and valleys. But these surfaces are angled and not flat, so you are actually getting more surface area contact. This is because some parts of the pad are contacting the rotor at an angle, and some are contacting at a different angle, but most of the contact is not directly flat. This is a good thing, as more surface area gives more area for heat to be dissapated over, allowing the overall brakes to run a bit cooler when they get hot
BRAKE IN PROCEDURE:
--I will assume the car has 4 balanced wheels and tires, and properly torqued lug nuts and that the brakes were installed correctly, by a shop, dealer, or Honda service manual instructions.
Find a big, open piece of asphalt. If you do not have one, try and find a semi-empty road that will allow plenty of room to stop and that doesn't have a lot of traffic or empty neighbors (common sense goes a long way here.)
Push the pedal a few times to make sure the pads are contacting. When you installed your pads, the pistons were compressed, and you don't want to hit the brakes and have the first stroke only move the piston and not stop the car.
Get the car upto about 60mph. press the pedal to about half pedal stroke, not full braking, but about half that. Slow the car to about 10mph but do not let it come to a complete stop. Get the car back upto 60mph after this, not giving the brakes a lot of time to cool, and again, slow the car to about 10mph. Repeat this until the car has had 10 good stops. This will be removing any of the very raised edges by wearing the pads a little to increase the contact between the pad and the rotor to the full contact shape of the pad. Drive the car for a minute without stopping and slowly pull to a stop. Let the brakes cool completely to ambient air temperature. This is because if you were to stop the car each time, the hot pad will expand that part of the rotor but not the rest of it. i know it doesn't seem like much but it can cause sides of the rotor to be very slight differences in thickness, which, over time, will show up as vibration and reduce the stopping power of your brakes.
Repeat this procedure again, going from 60-10 another 10 times or so and let the brakes cool completely. This may require more stopping if say you have a lighter car with performance pads, than with a heavier car with less aggressive pads made for longevity. As you are going through these 60-10 stops, you will notice that as the brakes warm up and brake in, your car will stop sooner and sooner each time. If the car gets better and better and suddenly one time it feels like the brakes have just stopped working and you have to press very hard, slow the car and drive slowly as the brakes may have overheated. Keep driving slowly in circles or in a line as stopping while the brakes are new and this hot can cause a poor brake in.
This is a good, basic brake in procedure that I have used on all 17 different brake setups I have had on my Civic, over 4 sets of tires and many, many brake pads and I have never had any brake vibration.
Though it is always reccomended to only install new pads and new or resurfaced rotors, this is applicable to new pads/used rotors, used pads/new rotors, or used pads/used rotors. This is more critical for used pads and used rotors, as both have bedded in differently and the first stop may have even less contact. Note that rotors with raised and lowered rings (like its bumpy running your finger across) will take a lot longer to bed in, ie it wont take 100 miles, but upto 5000 miles. Those rotors are likely not within OE runout speficiation and will need resurfacing or replacing and are not reccomended to be used at all.
Side note: Our Hondas have kick *** brake systems. Our brakes tend to be very quiet stock, given the well engineered pad shapes Honda comes up with. Other cars, especially GM and Ford can go through this procedure but still have noise. This is from the light vibration of the rotor that shows up as a squeal. I will always reccomend using the OEM brake pad SHIMS. Shims are thin pieces of metal that clip to the back of a brake pad. Though most all Hondas with all styles of pads/rotors can be free of this annoying squeal without shims, using shims with an anti-vibration compound between them and the pad will reduce any noise with any pad except full metal race pads. The anti-vibration compound can be bought at any auto store and is usually a gooey, tacky substance that turns into a rubber compound and absorbs these tiny vibrations, keeping the brakes nice and quiet. This is much more of a necessity on cars like Fords and GMs with 2 piston calipers where the pad is symmetrical and so are the piston sizes.
When you get new pads and rotors, the pads and rotors are not going to initally give full braking. This is because the surface does not give full contact. Both surfaces are not completly smooth, they may have bumps and dips that are small fractions of a millimeter that you cannot see. But when they are new and touch for the first stop, its possible that only 10% of the actual pad touches the actual metal of the rotor. So for your first hard stop, the car not stop anywhere near what you'd expect.
diagram 1.
This is a crude picture I know, but this is what most of your brake setups would look like from the side. That piston is going to push the inner pad, and there is a slide pin that allows the caliper to move, and will make the caliper pull on the outer pad too, toward the rotor. Notice that it looks like the pad and rotor are totally smooth, and your brakes to the naked eye will seem that way when they are new.
To remedy this, you want both surfaces to have their small raises and dips compliment each other, increasing surface contact. Remember, disc brakes work by pushing two pads against a spinning disc, and using the friction, slow the disc's rotation thus slowing the car.
diagram 2.
Another crude picture, but if you were to zoom in on the pad and rotor enough, the surfaces would be something like this. See the gaps between them. Becuase the raised parts are so small, and that there will me the same force applied over less area, the pressure will be increased. During the first stop, this will be felt as a quick nose dive in the car. Since these raised parts are so small, they will wear out very fast, which is the purpose of the brake in procedure. You wear out the raised parts of the pad, and as it wears, digs into the rotor, and the lowered parts of the pad will then hit the untouched and now relatively raised part of the rotor. When the brakes are used enough through the brake-in period, you should have the whole pad contact the rotor like in the first picture.
diagram 3.
When the pads will break in and the car is then driven most of the pad's life, it will look something like this. You will see they are still uneven. A flat contact surface would net 100% the surface area of the pad. Since there are these raised and lower parts, its as if there are mountain ranges and valleys. But these surfaces are angled and not flat, so you are actually getting more surface area contact. This is because some parts of the pad are contacting the rotor at an angle, and some are contacting at a different angle, but most of the contact is not directly flat. This is a good thing, as more surface area gives more area for heat to be dissapated over, allowing the overall brakes to run a bit cooler when they get hot
BRAKE IN PROCEDURE:
--I will assume the car has 4 balanced wheels and tires, and properly torqued lug nuts and that the brakes were installed correctly, by a shop, dealer, or Honda service manual instructions.
Find a big, open piece of asphalt. If you do not have one, try and find a semi-empty road that will allow plenty of room to stop and that doesn't have a lot of traffic or empty neighbors (common sense goes a long way here.)
Push the pedal a few times to make sure the pads are contacting. When you installed your pads, the pistons were compressed, and you don't want to hit the brakes and have the first stroke only move the piston and not stop the car.
Get the car upto about 60mph. press the pedal to about half pedal stroke, not full braking, but about half that. Slow the car to about 10mph but do not let it come to a complete stop. Get the car back upto 60mph after this, not giving the brakes a lot of time to cool, and again, slow the car to about 10mph. Repeat this until the car has had 10 good stops. This will be removing any of the very raised edges by wearing the pads a little to increase the contact between the pad and the rotor to the full contact shape of the pad. Drive the car for a minute without stopping and slowly pull to a stop. Let the brakes cool completely to ambient air temperature. This is because if you were to stop the car each time, the hot pad will expand that part of the rotor but not the rest of it. i know it doesn't seem like much but it can cause sides of the rotor to be very slight differences in thickness, which, over time, will show up as vibration and reduce the stopping power of your brakes.
Repeat this procedure again, going from 60-10 another 10 times or so and let the brakes cool completely. This may require more stopping if say you have a lighter car with performance pads, than with a heavier car with less aggressive pads made for longevity. As you are going through these 60-10 stops, you will notice that as the brakes warm up and brake in, your car will stop sooner and sooner each time. If the car gets better and better and suddenly one time it feels like the brakes have just stopped working and you have to press very hard, slow the car and drive slowly as the brakes may have overheated. Keep driving slowly in circles or in a line as stopping while the brakes are new and this hot can cause a poor brake in.
This is a good, basic brake in procedure that I have used on all 17 different brake setups I have had on my Civic, over 4 sets of tires and many, many brake pads and I have never had any brake vibration.
Though it is always reccomended to only install new pads and new or resurfaced rotors, this is applicable to new pads/used rotors, used pads/new rotors, or used pads/used rotors. This is more critical for used pads and used rotors, as both have bedded in differently and the first stop may have even less contact. Note that rotors with raised and lowered rings (like its bumpy running your finger across) will take a lot longer to bed in, ie it wont take 100 miles, but upto 5000 miles. Those rotors are likely not within OE runout speficiation and will need resurfacing or replacing and are not reccomended to be used at all.
Side note: Our Hondas have kick *** brake systems. Our brakes tend to be very quiet stock, given the well engineered pad shapes Honda comes up with. Other cars, especially GM and Ford can go through this procedure but still have noise. This is from the light vibration of the rotor that shows up as a squeal. I will always reccomend using the OEM brake pad SHIMS. Shims are thin pieces of metal that clip to the back of a brake pad. Though most all Hondas with all styles of pads/rotors can be free of this annoying squeal without shims, using shims with an anti-vibration compound between them and the pad will reduce any noise with any pad except full metal race pads. The anti-vibration compound can be bought at any auto store and is usually a gooey, tacky substance that turns into a rubber compound and absorbs these tiny vibrations, keeping the brakes nice and quiet. This is much more of a necessity on cars like Fords and GMs with 2 piston calipers where the pad is symmetrical and so are the piston sizes.
04-09-2012, 10:11 AM
#2
Re: Brake in procedure - for changing pads and/or rotors
The break-in procedure is good, but the fundamentals are a little off. You want to break-in the pads for more than JUST getting the pad and rotor to match shape. It's also done to burn off any mold-release compound from the manufacturing process (why Centric pre-scorches some of their pads), as well as transfer a layer of pad friction material onto the iron surface of the rotor. Both of these facts help to increase your coefficient of friction, while the surface contact area of the pad does not.
2nd, your pad material is much much softer than the rotor (unless you've got a carbon-brake rotor option). The pads should not instantly wear grooves into the rotors upon break-in. If anything, the rotor will smooth off the high spots on the pads.
2nd, your pad material is much much softer than the rotor (unless you've got a carbon-brake rotor option). The pads should not instantly wear grooves into the rotors upon break-in. If anything, the rotor will smooth off the high spots on the pads.
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