I found that very agressive break in of Akebano pads resulted in the feel of rotor warp after about 20,000 miles. I now use a far less agressive process with those same pads on new rotors with no feel of warpage. Just my experience with a Chrysler mini-van and a PT Cruiser.
Pad Bed-In: Harmful
- Thread starter The Critic
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interesting. thats not supprising considering they dyno test the engines and all that. wonder if porsche or audi tests their cars as much as chevy does to the vette?
in any case, take an ordinary commuter car, ya think the factory beds in the pads o these cars? ill give ya a hint, vw has a car carousel that delivers the car to the new oener with 0.0 miles on the odometer. cant bed in the brakes when the cars never been driven before
I remeber when My dad Had a 1995 Honda Accord with a recent brake job, and Mom bought a 1999 Honda CRV. They both were told that their brake pads worked best by using them gently for the first 500 miles. They both were also noisy for the first 500 miles.
Shame on you Mike for drawing me into this
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Here is my take/experience on all of this. First, we need to define friction types and the differences between them. Adherent friction is when bonds are formed and then broken on a molecular level. This is generally regarded as the most desirable type of friction for braking. Abrasive friction is, like it's name implies, the friction created by the pad rubbing against the rotor. This is ok, but not quite as strong (regarding brakes) as adherent friction. So how do we produce these frictions? Abrasive is easy. You don't have to do anything other than operate the braking system. Adherent is a little tougher. First you must have like material on both "sides" of the system, pad and rotor. A thin film of pad material transferred to the rotor surface will create this. Then when we operate the brakes, the bonding/bond breaking action will occur. It takes high heat for this material transfer to happen, basically it is melting the pad. Once done (properly), Viola! Adherent fricition.
Most street applications operate at low temps and pads are compounded to provide better bite/stopping power when cold. Thats a reason for all the dust but it also tempers noise too. Push a street pad though, and it reaches MOT (maximum operating temperature) fairly quickly. Go above MOT and you get fade. Basically its where the pad/rotor cannot shed heat faster than it is accumulating it.
A performance pad is compounded to operate at a higher MOT, but sometimes with a price. Usually it is less initial bite. Thats because they need a bit more heat before the compound starts to work as designed. The balancing act that performance pad designers perform is to get good braking right off the bat (dead cold) and still work at higher temps than the regular street pads do. Add the desired traits of less noise and dust we can start to see how hard this razor's edge of pad compounding is for a manufacturer to walk.
Ok, so how does all this play with regards to the Akebono pads? Well, they have designed a pad to work extremely well when cold, have significantly less dust and noise, and have low wear. They have also designed it to transfer pad material slowly and with lower temps. This means, generally, material transfer will occur with normal driving. But it takes awhile. Material transfer can be done quicker with bedding, BUT, you MUST take into consideration just what type of material you are working with. The good folks over at Akebono understand that most people don't have a clue about adherent or abrasive fricitions, much less what bedding pads is all about. This blissful ignorance is why they built in the burnishing to occur over routine use and why they don't recommend any type of bed-in. They can only imagine the liablity if they told folks to go out and bed-in their pads not knowing how to do so.
A performance pad will take a series of hard stops to generate the heat needed for material transfer. The Ake's, not so much. I glazed a set on my truck when I performed my "usual" 8-10 hard stops with them. I should have sensed something was wrong when they went to fade after 3 stops and started smoking, BAD. Usually don't hit fade and smell til about stop #6 with other (performance) pads. BTW, you should still do another 1-3 stops after fade and smell to insure the uniform transfer of material. I broke the glaze and then tried a significantly less aggressive 3 stop bed-in. Now they work fine. I also have the Akebonos in the mini-van. No bed-in and they work fine too. I attribute this to the fact that the van is a much heavier vehicle and generates more heat than the much lighter truck does. Of course, YMMV.
Here is my take/experience on all of this. First, we need to define friction types and the differences between them. Adherent friction is when bonds are formed and then broken on a molecular level. This is generally regarded as the most desirable type of friction for braking. Abrasive friction is, like it's name implies, the friction created by the pad rubbing against the rotor. This is ok, but not quite as strong (regarding brakes) as adherent friction. So how do we produce these frictions? Abrasive is easy. You don't have to do anything other than operate the braking system. Adherent is a little tougher. First you must have like material on both "sides" of the system, pad and rotor. A thin film of pad material transferred to the rotor surface will create this. Then when we operate the brakes, the bonding/bond breaking action will occur. It takes high heat for this material transfer to happen, basically it is melting the pad. Once done (properly), Viola! Adherent fricition.
Most street applications operate at low temps and pads are compounded to provide better bite/stopping power when cold. Thats a reason for all the dust but it also tempers noise too. Push a street pad though, and it reaches MOT (maximum operating temperature) fairly quickly. Go above MOT and you get fade. Basically its where the pad/rotor cannot shed heat faster than it is accumulating it.
A performance pad is compounded to operate at a higher MOT, but sometimes with a price. Usually it is less initial bite. Thats because they need a bit more heat before the compound starts to work as designed. The balancing act that performance pad designers perform is to get good braking right off the bat (dead cold) and still work at higher temps than the regular street pads do. Add the desired traits of less noise and dust we can start to see how hard this razor's edge of pad compounding is for a manufacturer to walk.
Ok, so how does all this play with regards to the Akebono pads? Well, they have designed a pad to work extremely well when cold, have significantly less dust and noise, and have low wear. They have also designed it to transfer pad material slowly and with lower temps. This means, generally, material transfer will occur with normal driving. But it takes awhile. Material transfer can be done quicker with bedding, BUT, you MUST take into consideration just what type of material you are working with. The good folks over at Akebono understand that most people don't have a clue about adherent or abrasive fricitions, much less what bedding pads is all about. This blissful ignorance is why they built in the burnishing to occur over routine use and why they don't recommend any type of bed-in. They can only imagine the liablity if they told folks to go out and bed-in their pads not knowing how to do so.
A performance pad will take a series of hard stops to generate the heat needed for material transfer. The Ake's, not so much. I glazed a set on my truck when I performed my "usual" 8-10 hard stops with them. I should have sensed something was wrong when they went to fade after 3 stops and started smoking, BAD. Usually don't hit fade and smell til about stop #6 with other (performance) pads. BTW, you should still do another 1-3 stops after fade and smell to insure the uniform transfer of material. I broke the glaze and then tried a significantly less aggressive 3 stop bed-in. Now they work fine. I also have the Akebonos in the mini-van. No bed-in and they work fine too. I attribute this to the fact that the van is a much heavier vehicle and generates more heat than the much lighter truck does. Of course, YMMV.
And once again, the wonderful world of internet misinformation rears its ugly head.
OK, here's some information on brake pads and bedding procedures.
First of all, it's important to note that there are many kinds of different brake pads with different compositions, different optimal operating temperature ranges and different mechanical characteristics.
Optimally in this current day and age, the best brake pads function by adherent friction. Older brake pads tend to work by abrasive friction. You'll find some explanation of this in the Stoptech pad bedding white papers and their 'Myth of Warped Rotors' articles.
Adherent friction is somewhat akin to trying to slide a 3M Post-It note across a table. Abrasive friction is akin to sliding a piece of sandpaper across the table. It is also possible for the same pad to exhibit both characteristics at different operating temperatures (this is common with race or very high performance, high MOT Maximum-Operating-Temperature pads where they are abrasive at low temps and adherent at high temps).
In the old days, the vast majority of brake pads used abrasive friction. The main reason for bedding-in pads was to cook off the excess resin binder that holds the pad material together. When a new pad got really hot for the first time, these resins binders would liquefy and or gas out and could decrease braking performnce significantly (acting as a liquid or gas layer separating the pads from the rotors). This phenomenon is known as 'green fade'. Pad bed-in was meant to evaporate/cook off the excess binders so this wouldn't happen on the road/track. Folks discovered that another way to do it aside from aggressive bed-in on street/track was to stick the pads in the barbecue grill for 15 minutes accomplising the same thing. Newer pads though have a much lower tendency to experience this problem (as resin binder compositions improve).
On the other side, in order for a brake pad using adherent friction to generate it's greatest braking torque, it is necessary to form a thin film of pad material on the surface of the rotor because the brake pad's adherent chemical bonds that it forms under heat and pressure work best sticking to itself (the pad material to the layer of pad material on the rotor).
In order to deposit a good even layer of this pad material on the rotor, it is necessary to get the pads and rotors up to the point where the pad material heats up enough to start depositing pad material. You also need sufficient pressure to ensure that the material layer on the rotor is both thin and even.
Brake pads using adherent friction can generate much greater braking torque than abrasive pads and they also tend to be much gentler on the rotors than the abrasive pads. Most if not all 'Lifetime' pads are abrasive in nature. They are rock hard, tend to have lower mu (mu being the pad's coefficient of friction) and they eat rotors. The pads may last a lifetime of careful driving, but your rotors will not. They are exchanging wear on the pads for excessive wear on the rotors.
In the performance world (read as racing world), no one bother with abrasive type pads anymore. They aren't worth the time. Now with adherent pads, it's possible to finish an endurance event with the rotors measuring the same thickness (or even potentially microscopically thicker) due to the pad material deposition where abrasive friction type pads would have worn the rotors to potentially discard thickness.
Now where does this tie in with the different bed-in procedures? It matters what kind of pads you are using. Most of the current performance adherent friction based pads perform best with the aggressive break-in. The aggressive break-in is designed to heat the pads and rotors up to the optimal operating temperature for the material to start leaving a deposit layer on the rotors. The medium-high pressure (generally done with braking to 75% of wheel lockup, meaning you're not locking up the wheels but coming close) is intended to ensure the deposited pad material layer is thin and even. It also burns off any excess binder to prevent green fade.
With hard abrasive pads though, there is no formation of this pad material deposit on the rotors and thus, no need for the aggressive break-in. All you'ld be doing is eating your rotors up quicker. The mild break-in is enough to burn off the little excess binder.
As an example of the different pad compositions and necessity for different practices, the pad that I currently have on my street car (that I also run on roadcourses) is a high performance pad (Carbotech Panther Plus)and is not really recommended for street use due to increased dust and noise. Its optimal operating temp range is also higher than is normal for street pads. Under track use, the pad is quite happy, however, it needs quite more heat than average to be happy on the street. In order to maintain a layer of pad material on the rotors, I need to ensure that at least every few days of driving, I engage in a few medium hard braking events. If I don't do this, the pad will scrub off the deposit layer on the rotor and work by abrasive friction. Although the pad generates good braking torque even when cold (I've driven it in the winter), the maximum braking torque is when the pad is hot and the mechanism is via adherent friction.
Another such pad (not to be used on the street at all) is the Hawk Blue race pad. This pad is meant strictly for race use. Wen used on the track, it's actually quite a good pad, but the rotors and ads must maintain quite a bit of heat for the pad to function in adherent fashion. If the pad is driven on the street it's not possible to get it hot enough and it is extremely abrasive, so much so that Stoptech recommends using the pad for 50 miles or so in street driving as an alternative to turning the rotors to remove previous pad material in preparation for bedding in a new/different pad material.
Oh, and one last thing. Adherent pad compositions may not be very nice to each other, i.e. if you're switching from one kind of adherent pad to another with a different composition, you might find that it is very difficult to bed-in the new pads due to the deposited layer of the old pad left on the rotors. This is why it's a good idea to have the rotors turned if you're switching pad types and reusing the old rotors. For instance the Carbotech pads don't bed-in properly if the rotors were previously used with Hawk pads. It takes much longer to properly bed them in if the rotors were not turned (or cleaned by street driving them with Hawk Blues etc.) and while the new pads are trying unsuccessfully to bed-in with the old pad material on the rotors, braking torque is significantly lower than it would be if the pads were bedded-in properly.
Oh and just for more info, Carbotech Panther Plus pads have a mu of about 0.5 to 0.55 and an MOT of ~1300 fahrenheit. Most street pads that you can buy at Autozone or pep Boys and such have a mu range of about 0.3 - 0.4, an MOT of about 750-900f, work OK when they're cold and you can generally get pad fade fairly easily from too much hard braking.
Max
OK, here's some information on brake pads and bedding procedures.
First of all, it's important to note that there are many kinds of different brake pads with different compositions, different optimal operating temperature ranges and different mechanical characteristics.
Optimally in this current day and age, the best brake pads function by adherent friction. Older brake pads tend to work by abrasive friction. You'll find some explanation of this in the Stoptech pad bedding white papers and their 'Myth of Warped Rotors' articles.
Adherent friction is somewhat akin to trying to slide a 3M Post-It note across a table. Abrasive friction is akin to sliding a piece of sandpaper across the table. It is also possible for the same pad to exhibit both characteristics at different operating temperatures (this is common with race or very high performance, high MOT Maximum-Operating-Temperature pads where they are abrasive at low temps and adherent at high temps).
In the old days, the vast majority of brake pads used abrasive friction. The main reason for bedding-in pads was to cook off the excess resin binder that holds the pad material together. When a new pad got really hot for the first time, these resins binders would liquefy and or gas out and could decrease braking performnce significantly (acting as a liquid or gas layer separating the pads from the rotors). This phenomenon is known as 'green fade'. Pad bed-in was meant to evaporate/cook off the excess binders so this wouldn't happen on the road/track. Folks discovered that another way to do it aside from aggressive bed-in on street/track was to stick the pads in the barbecue grill for 15 minutes accomplising the same thing. Newer pads though have a much lower tendency to experience this problem (as resin binder compositions improve).
On the other side, in order for a brake pad using adherent friction to generate it's greatest braking torque, it is necessary to form a thin film of pad material on the surface of the rotor because the brake pad's adherent chemical bonds that it forms under heat and pressure work best sticking to itself (the pad material to the layer of pad material on the rotor).
In order to deposit a good even layer of this pad material on the rotor, it is necessary to get the pads and rotors up to the point where the pad material heats up enough to start depositing pad material. You also need sufficient pressure to ensure that the material layer on the rotor is both thin and even.
Brake pads using adherent friction can generate much greater braking torque than abrasive pads and they also tend to be much gentler on the rotors than the abrasive pads. Most if not all 'Lifetime' pads are abrasive in nature. They are rock hard, tend to have lower mu (mu being the pad's coefficient of friction) and they eat rotors. The pads may last a lifetime of careful driving, but your rotors will not. They are exchanging wear on the pads for excessive wear on the rotors.
In the performance world (read as racing world), no one bother with abrasive type pads anymore. They aren't worth the time. Now with adherent pads, it's possible to finish an endurance event with the rotors measuring the same thickness (or even potentially microscopically thicker) due to the pad material deposition where abrasive friction type pads would have worn the rotors to potentially discard thickness.
Now where does this tie in with the different bed-in procedures? It matters what kind of pads you are using. Most of the current performance adherent friction based pads perform best with the aggressive break-in. The aggressive break-in is designed to heat the pads and rotors up to the optimal operating temperature for the material to start leaving a deposit layer on the rotors. The medium-high pressure (generally done with braking to 75% of wheel lockup, meaning you're not locking up the wheels but coming close) is intended to ensure the deposited pad material layer is thin and even. It also burns off any excess binder to prevent green fade.
With hard abrasive pads though, there is no formation of this pad material deposit on the rotors and thus, no need for the aggressive break-in. All you'ld be doing is eating your rotors up quicker. The mild break-in is enough to burn off the little excess binder.
As an example of the different pad compositions and necessity for different practices, the pad that I currently have on my street car (that I also run on roadcourses) is a high performance pad (Carbotech Panther Plus)and is not really recommended for street use due to increased dust and noise. Its optimal operating temp range is also higher than is normal for street pads. Under track use, the pad is quite happy, however, it needs quite more heat than average to be happy on the street. In order to maintain a layer of pad material on the rotors, I need to ensure that at least every few days of driving, I engage in a few medium hard braking events. If I don't do this, the pad will scrub off the deposit layer on the rotor and work by abrasive friction. Although the pad generates good braking torque even when cold (I've driven it in the winter), the maximum braking torque is when the pad is hot and the mechanism is via adherent friction.
Another such pad (not to be used on the street at all) is the Hawk Blue race pad. This pad is meant strictly for race use. Wen used on the track, it's actually quite a good pad, but the rotors and ads must maintain quite a bit of heat for the pad to function in adherent fashion. If the pad is driven on the street it's not possible to get it hot enough and it is extremely abrasive, so much so that Stoptech recommends using the pad for 50 miles or so in street driving as an alternative to turning the rotors to remove previous pad material in preparation for bedding in a new/different pad material.
Oh, and one last thing. Adherent pad compositions may not be very nice to each other, i.e. if you're switching from one kind of adherent pad to another with a different composition, you might find that it is very difficult to bed-in the new pads due to the deposited layer of the old pad left on the rotors. This is why it's a good idea to have the rotors turned if you're switching pad types and reusing the old rotors. For instance the Carbotech pads don't bed-in properly if the rotors were previously used with Hawk pads. It takes much longer to properly bed them in if the rotors were not turned (or cleaned by street driving them with Hawk Blues etc.) and while the new pads are trying unsuccessfully to bed-in with the old pad material on the rotors, braking torque is significantly lower than it would be if the pads were bedded-in properly.
Oh and just for more info, Carbotech Panther Plus pads have a mu of about 0.5 to 0.55 and an MOT of ~1300 fahrenheit. Most street pads that you can buy at Autozone or pep Boys and such have a mu range of about 0.3 - 0.4, an MOT of about 750-900f, work OK when they're cold and you can generally get pad fade fairly easily from too much hard braking.
Max
And I thought my explanation was long-winded
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Seriously, max expanded on the info and presented some more insight. Especially true regarding pad material incompatibility. The old racer's adage about using new pads on old (seasoned) rotors and vice-versa applied when using the same pads. This is because the old rotors still had a material layer on them and the old pads were already "gassed", meaning binder material was already cooked off and would not affect heat tempering of new rotors. Different pad compounds generally don't play well together when switched around on existing rotors. Thus the reason behind skimming to get a fresh surface.
Again as bluemax explained, a rotor operated in adherent mode will last for a very long time. Because the friciton is occuring within the pad material bond/bond breaking, abrasive friction is kept to a minimum and also it's subsequent high wear.
Lots of folks are are now using the same rotors for track use and street use and only changing pads for the events. How does this work after I just explained that a "new" surface should be provided for a different compound to work well? Easy. Switch to the track pads prior to the event and drive (carefully!) to the venue. They operate in primarily abrasive mode until heated to their proper, working temp. range. This in effect scrubs the material layer from the street pads off and gives a fresh surface for the race pads. At the track (usually during practice sessions) the pads are heated and the transfer of material (bedding) occurs. By race time, there is sufficient material transfer to work well for the event. Afterwards, when everything has cooled down, the track pads return to abrasive mode and scrub off the pad material they laid down for the track event. Another careful drive home on the track pads produces another fresh surface, all ready for the street pads to do their thing after a round of bedding. Guys I've talked with that use this method report the rotors lasting quite a long time in spite of the severe track use.
Seriously, max expanded on the info and presented some more insight. Especially true regarding pad material incompatibility. The old racer's adage about using new pads on old (seasoned) rotors and vice-versa applied when using the same pads. This is because the old rotors still had a material layer on them and the old pads were already "gassed", meaning binder material was already cooked off and would not affect heat tempering of new rotors. Different pad compounds generally don't play well together when switched around on existing rotors. Thus the reason behind skimming to get a fresh surface.
Again as bluemax explained, a rotor operated in adherent mode will last for a very long time. Because the friciton is occuring within the pad material bond/bond breaking, abrasive friction is kept to a minimum and also it's subsequent high wear.
Lots of folks are are now using the same rotors for track use and street use and only changing pads for the events. How does this work after I just explained that a "new" surface should be provided for a different compound to work well? Easy. Switch to the track pads prior to the event and drive (carefully!) to the venue. They operate in primarily abrasive mode until heated to their proper, working temp. range. This in effect scrubs the material layer from the street pads off and gives a fresh surface for the race pads. At the track (usually during practice sessions) the pads are heated and the transfer of material (bedding) occurs. By race time, there is sufficient material transfer to work well for the event. Afterwards, when everything has cooled down, the track pads return to abrasive mode and scrub off the pad material they laid down for the track event. Another careful drive home on the track pads produces another fresh surface, all ready for the street pads to do their thing after a round of bedding. Guys I've talked with that use this method report the rotors lasting quite a long time in spite of the severe track use.
Tks. Had (still have) the same kind of obsession with brakes as I do now for oil
Learned about braking systems and their components long before BITOG, and learned the hard way! By trying different things and sometimes ending up with serious "pucker" factor from my trials. It lets you know real quick when you've done something silly when you push the brake pedal and it sinks to the floor. The armco you are about to collect as a hood ornament at 100+ does the trick too
They used to call me Mr. Brake during my years as an instructor at the Police Academy's track. I told them going fast is cool, but stopping is even better (and NOT the sudden -40g kind
Sorry all, for the boring, self fulfilling background on me
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