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Thread: Pad and Rotor Bed-In Theory, Definitions and Procedures

  1. #1
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    Pad and Rotor Bed-In Theory, Definitions and Procedures

    http://www.stoptech.com/tech_info/wp...contents.shtml

    Removing the Mystery from Brake Pad Bed-In

    In order for any brake system to work optimally, the rotors and pads must be properly bedded-in, period. This process can also be called break-in, conditioning, or burnishing, but whatever terminology you choose, getting the brakes properly bedded-in and keeping them that way is critical to the peak performance of the entire brake system.

    However, understanding why the rotors and pads need to be bedded-in is just as important as the actual process. If one understands what is happening during the bed-in process, they can tailor the process to specific pads, rotors, and/or driving conditions. For this reason, we present this generic bed-in overview pertaining to all brake systems, but follow with links to application-specific bed-in procedures to fit most every set of circumstances.

    What is brake pad �bed-in� anyway?


    Simply stated, bed-in is the process of depositing an even layer of brake pad material, or transfer layer, on the rubbing surface of the rotor disc. That�s it. End of discussion. Ok, not really, but although bed-in is quite basic in definition, achieving this condition in practice can be quite a challenge, and the ramifications of improper or incomplete bed-in can be quite a-a-n-n-o-o-y-y-i-i-n-n-g-g.

    Abrasive friction and adherent friction

    There are two basic types of brake pad friction mechanisms: abrasive friction and adherent friction. In general, all pads display a bit of each, with abrasive mechanisms dominating the lower temperature ranges while adherent mechanisms come more into play as pad temperature increases. Both mechanisms allow for friction or the conversion of Kinetic energy to Thermal energy, which is the function of a brake system, by the breaking of molecular bonds in vastly different ways.

    The abrasive mechanism generates friction or energy conversion by the mechanical rubbing of the brake pad material directly on the rotor disc. In a crystalline sense, the weaker of the bonds in the two different materials is broken. This obviously results in mechanical wear of both the pad and the rotor. Consequently, both pads and rotors are replaced when they are physically worn to their limit and are too thin to endure further service.

    The adherent mechanism is altogether different. In an adherent system, a thin layer of brake pad material actually transfers and sticks (adheres) on to the rotor face. The layer of pad material, once evenly established on the rotor, is what actually rubs on the brake pad. The bonds that are broken, for the conversion of Kinetic to Thermal energy, are formed instantaneously before being broken again. It is this brake pad-on-transferred brake pad material interaction on a molecular level that yields the conversion process.

    With the adherent mechanism there is much reduced rotor wear as compared to abrasive mechanism, but it�s not a free lunch � pads now become the primary wear element in the braking system. And even though rotors are not mechanically worn down with adherent systems, they still will need to be replaced on a regular basis due to cracking reaching a point of failure if they are exposed to intense, repetitive thermal cycling. This is why race teams throw out rotors that are actually as thick or thicker than when they were brand new. It�s due to the an adherent brake pad transfer layer!

    The all-important transfer layer

    As stated above, the objective of the bed-in process is to deposit an even layer of brake pad material, or transfer layer, on the rubbing surface of the rotor disc. Note the emphasis on the word even, as uneven pad deposits on the rotor face are the number one, and almost exclusive cause of brake judder or vibration.

    Let�s say that again, just so there is no misunderstanding. Uneven pad deposits on the rotor face are the number one, and almost exclusive cause of brake judder or vibration.

    It only takes a small amount of thickness variation, or TV, in the transfer layer (we're only talking a few ten thousandths of an inch here) to initiate brake vibration. While the impact of an uneven transfer layer is almost imperceptible at first, as the pad starts riding the high and low spots, more and more TV will be naturally generated until the vibration is much more evident. With prolonged exposure, the high spots can become hot spots and can actually change the metallurgy of the rotor in those areas, creating �hard� spots in the rotor face that are virtually impossible to remove.

    Bedding fundamentals

    In general, bed-in consists of heating a brake system to its adherent temperature to allow the formation of a transfer layer. The brake system is then allowed to cool without coming to rest, resulting in an even transfer layer deposition around the rotor circumference. This procedure is typically repeated two or three times in order to ensure that the entire rotor face is evenly covered with brake pad material. Sounds easy, right? Well, it can be if you have the proper information.

    Because the adherent temperature range for brake pads varies widely (typically 100�F-600�F for street pads and 600�F-1400�F for race pads), each bed-in needs to be application-specific. One could try to generate a one-size-fits-all procedure, but too little heat during bed-in keeps the material from transferring to the rotor face while overheating the system can generate uneven pad deposits due to the material breaking down and splotching (that�s a technical term) on to the rotor face.

    In summary, the key to a successful bed-in is to bring the pads up to their adherent operating temperature in a controlled manner and keep them there long enough to start the pad material transfer process. Different brake system designs, pad types, and driving conditions require different procedures to successfully accomplish the bed-in. The recommended procedures below should provide you with the information you need to select the bed-in procedure appropriate for your application.


    StopTech�s Recommended Procedure for Bedding-in Stock-Sized Brake Systems

    When a system has both new rotors and pads, there are two different objectives for bedding-in a performance brake system: heating up the brake rotors and pads in a prescribed manner, so as to transfer pad material evenly onto the rotors; and maturing the pad material, so that resins which are used to bind and form it are �cooked� out of the pad.

    The first objective is achieved by performing a series of stops, so that the brake rotor and pad material are heated steadily to a temperature that promotes the transfer of pad material onto the brake rotor friction surface. There is one pitfall in this process, however, which must be avoided. The rotor and, therefore, the vehicle should not be brought to a complete stop, with the brakes still applied, as this risks the non-uniform transfer of pad material onto the friction surface.

    The second objective of the bedding-in process is achieved by performing another set of stops, in order to mature the pad itself. This ensures that resins which are used to bind and form the pad material are �cooked� out of the pad, at the point where the pad meets the rotor�s friction surface.

    The bed-in process is not complete until both sets of stops have been performed.

    Bedding-in Street Performance Pads


    For a typical performance brake system using street-performance pads, a series of ten partial braking events, from 60mph down to 10mph, will typically raise the temperature of the brake components sufficiently to be considered one bed-in set. Each of the ten partial braking events should achieve moderate-to-high deceleration (about 80 to 90% of the deceleration required to lock up the brakes and/or to engage the ABS), and they should be made one after the other, without allowing the brakes to cool in between.

    Depending on the make-up of the pad material, the brake friction will seem to gain slightly in performance, and will then lose or fade somewhat by around the fifth stop (also about the time that a friction smell will be detectable in the passenger compartment). This does not indicate that the brakes are bedded-in. This phenomenon is known as a green fade, as it is characteristic of immature or �green� pads, in which the resins still need to be driven out of the pad material, at the point where the pads meet the rotors. In this circumstance, the upper temperature limit of the friction material will not yet have been reached.

    As when bedding-in any set of brakes, care should be taken regarding the longer stopping distance necessary with incompletely bedded pads. This first set of stops in the bed-in process is only complete when all ten stops have been performed - not before. The system should then be allowed to cool, by driving the vehicle at the highest safe speed for the circumstances, without bringing it to a complete stop with the brakes still applied. After cooling the vehicle, a second set of ten partial braking events should be performed, followed by another cooling exercise. In some situations, a third set is beneficial, but two are normally sufficient.

    Bedding-in Club Race or Full Race Pads

    For a typical performance brake system using race pads, the bed-in procedure must be somewhat more aggressive, as higher temperatures need to be reached, in order to bring certain brands of pad material up to their full race potential.

    We typically recommend a set of ten partial braking events, from 60mph down to 10mph, followed immediately by three or four partial braking events, from 80mph down to 10mph. Alternately, a set of eleven stops, from 80mph to 40mph, or a set of seven stops, from 100mph to 50mph, would be approximately the same. As with street pads, each of the partial braking events should achieve moderate-to-high deceleration (about 80% of the deceleration required to lock up the brakes and/or to engage the ABS), and they should be made one after the other, without allowing the brakes to cool in between.

    Again, depending on the make-up of the pad material, the brake friction will seem to gain slightly in performance, and will then lose or fade somewhat about halfway through the first set of stops. This does not indicate that the brakes are bedded-in, except where race-ready pads are being used. This phenomenon is the same as that which occurs with high-performance or street pads (except that, when race-ready pads are used, they do not exhibit green fade, and they will be bedded-in after just one complete set of stops).

    As when bedding-in any set of brakes, care should be taken regarding the longer stopping distance necessary with incompletely bedded pads. This first set of stops in the bed-in process is only complete when the recommended number of stops has been performed - not before. As a general rule, it would be better to perform additional stops, than not enough. The system should then be allowed to cool, by driving the vehicle at the highest safe speed for the circumstances, without bringing it to a complete stop with the brakes still applied.

    After cooling the vehicle, a second set of the recommended number of stops should be performed, followed by another cooling exercise. In some situations, a third set is beneficial, but two are normally sufficient.

    Racers will note that, when a pad is bedded-in properly, there will be approximately 2mm (0.1 inch) of the pad edge near the rotor, on which the paint will have turned to ash, or the color of the pad will have changed to look as though it has been overheated.

    In summary, the key to successfully bedding-in performance brakes is to bring the pads up to their operating temperature range, in a controlled manner, and to keep them there long enough to start the pad material transfer process. Different brake system designs, pad types, and driving conditions require different procedures to achieve a successful bed-in. The procedures recommended above should provide a useful starting point for developing bed-in procedures appropriate to individual applications.
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    Pad and Rotor Bed-In Theory, Definitions and Procedures

    sticky time :mrgreen: thanks for the info!!
    ''Yo, a$$G@@! This motherfucka's dead! Ain't no Chris Angel Mind freak, David Blaine trapdoor horseshit jumpin' off here!''

  3. #3

    Pad and Rotor Bed-In Theory, Definitions and Procedures

    good info...I'll definately use this procedure when I put on my Mu B-force pads.
    <br />&nbsp; Utec Hks272 camsÂ* Aem camgears ARPheadstuds 780 injectors Works Throttlebody 255 fuelpump RnR TBE,O2 &amp; 3&quot;intake Defi Bf Boost Gauge Hallman MBC 255/40Michelin PS2&#039;s Eibach Prokit springs Project Mu B-force ACT street clutch 10.5 Hotside injen intercooler pipes

  4. #4
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    Pad and Rotor Bed-In Theory, Definitions and Procedures

    Quote Originally Posted by gevo
    good info...I'll definately use this procedure when I put on my Mu B-force pads.
    I just did this process on my B-force pads last night. The pads squealed like hell the first four or five 60-10MPH runs i did. But after that, the squeal went away and i could smell burnt brake pad which gave me a bad headache. Just follow the instructions on the 1st post and you'll be a happy camper.

    I didn't push the brakes hard enough for the ABS to kickin because in my own opinion, the pulsating of the ABS system "might" cause uneven brake pad transfer onto the rotor. I say "might" because i'm making a guess that the ABS pulses the brakes when activated and i guess theoretically it could leave an uneven layer of pad deposit. I say better safe than sorry...
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  5. #5

    Pad and Rotor Bed-In Theory, Definitions and Procedures

    Quote Originally Posted by Skiracer
    Quote Originally Posted by gevo
    good info...I'll definately use this procedure when I put on my Mu B-force pads.
    I just did this process on my B-force pads last night. The pads squealed like hell the first four or five 60-10MPH runs i did. But after that, the squeal went away and i could smell burnt brake pad which gave me a bad headache. Just follow the instructions on the 1st post and you'll be a happy camper.

    I didn't push the brakes hard enough for the ABS to kickin because in my own opinion, the pulsating of the ABS system "might" cause uneven brake pad transfer onto the rotor. *I say "might" because i'm making a guess that the ABS pulses the brakes when activated and i guess theoretically it could leave an uneven layer of pad deposit. I say better safe than sorry...
    Did the squeal go away completely? *I know a couple of guys that have b-force and their brakes squeal under light braking.
    <br />&nbsp; Utec Hks272 camsÂ* Aem camgears ARPheadstuds 780 injectors Works Throttlebody 255 fuelpump RnR TBE,O2 &amp; 3&quot;intake Defi Bf Boost Gauge Hallman MBC 255/40Michelin PS2&#039;s Eibach Prokit springs Project Mu B-force ACT street clutch 10.5 Hotside injen intercooler pipes

  6. #6
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    Pad and Rotor Bed-In Theory, Definitions and Procedures

    Not sure if it went away completely since i dropped my car off at the dealership the next day and its still there now.
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  7. #7

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    Very good info

  8. #8

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    Great post... Question though, I know that some people lube their new pads. Is that necessary?
    Oh, and next Friday... is Hawaiian shirt day... so, you know, if you want to you can go ahead and wear a Hawaiian shirt and jeans.

  9. #9

    recommended brake pads

    What pads is prerferred for street/track use also where can I get the best deal


    Thanks in advance!!!

  10. #10

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    ss lines and good fluid will really make the bigger difference i was doing good with b-forces (with ss lines and rbf600) at SOW before i swithed to indepedent street /track setups

  11. #11

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    Quote Originally Posted by pensport
    What pads is prerferred for street/track use also where can I get the best deal


    Thanks in advance!!!
    Endless CC-X Pads 70% Track 30% street, contact jeff at 500whp.com

  12. #12

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    Use the Bedding-in Street Performance Pads method for Project Mu b-force pads correct?
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  13. #13

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    Wholy crap that was confusing... For those of us who have ADD, here's thequick version:
    For optimal brake performance, you bead-blast( or use another method to get the old pad material off 'em), install new pads, and then drive the car around,applying light/moderate brake pressure, off-and-on to bed in the new pads to the rotors.This introduces heat and then cooling to the pad/rotor surface in the right amount to get the pads properly mated to the rotors. It's crtical to only apply light/moderate brake presure so you don't glaze your brand-new $200 set of brake pads, and have to start over. It's quite easy to do.

  14. #14

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    ^^^ so it's light/moderate pressure? I've been hearing to apply considerably high pressure..
    &quot;Looney Tuned&quot;

  15. #15

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    Can this only be done on brand new pads? Changed mine a few months ago and they are squealers!
    This girl can drive!

  16. #16
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    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    I just got new rotors and brake pads, and someone said you can't install them at the same time. That doesn't make sense to me at all. Also, after installing them, does the braking you have to do to get to the freeway or road open enough to do the bed in procedure have any negative effect on the rotors? I would guess light braking until getting at high speed.

  17. #17

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    i always switch them both at the same time while always bleeding, always (helps the clutch too)
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  18. #18
    Evo Guru Azian's Avatar
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    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    You're either really bored or trying to sell something aren't you?

    Quote Originally Posted by dy4anevo
    i always switch them both at the same time while always bleeding, always (helps the clutch too)
    KT Motoring'Robispec

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  19. #19

    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    What about if your going to be running two sets of pads? Which set would you bed in on the rotors, ie. running posi-quiets for dd and switching to carbotech xp8's for the track? If you bed in the race pads will switching to another pad for dd mess up the transfer material, and if so does that mean you need to re-bed the track pads every time you go out to the track?

  20. #20
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    Re: Pad and Rotor Bed-In Theory, Definitions and Procedures

    Quote Originally Posted by gg9
    What about if your going to be running two sets of pads? Which set would you bed in on the rotors, ie. running posi-quiets for dd and switching to carbotech xp8's for the track? If you bed in the race pads will switching to another pad for dd mess up the transfer material, and if so does that mean you need to re-bed the track pads every time you go out to the track?
    Yes, everytime you swap pads you should lightly scuff the rotor with sand paper.
    KT Motoring'Robispec

    Fast cars drag race, fast drivers road race.

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