Front drum brakes, wheel loostening?

Discussion in 'Cycling Equipment' started by Chris Zacho "Th, May 26, 2003.

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  1. In the wake of the problems with the current front disk brake design and wheel ejection, the
    question comes up, what about front drum brakes?

    Since these are entirely internal, I wouldn't think they would suffer the same problem, but do they
    present a different one, due to any of their own possible design flaws? I'm not familiar with front
    DB design (are they like the rear, as far as wheel/fork attachment goes?).

    Consider the following circumstances, no lawyer lips, and either a QR or a nutted axle. and thanks
    for your response :-3)

    May you have the wind at your back. And a really low gear for the hills! Chris

    Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner
     
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  2. Jeff Wills

    Jeff Wills Guest

    [email protected] (Chris Zacho "The Wheelman") wrote in message
    news:<[email protected]>...
    > In the wake of the problems with the current front disk brake design and wheel ejection, the
    > question comes up, what about front drum brakes?
    >
    > Since these are entirely internal, I wouldn't think they would suffer the same problem, but do
    > they present a different one, due to any of their own possible design flaws? I'm not familiar with
    > front DB design (are they like the rear, as far as wheel/fork attachment goes?).
    >
    > Consider the following circumstances, no lawyer lips, and either a QR or a nutted axle. and thanks
    > for your response :-3)
    >

    Every drum brake front hub I've seen had a nutted axle and reaction arm that clamped to the fork
    blade. Both of these factors would make them less susceptible to the "Annan wheel ejection
    scenario". With the reaction arm in line with the fork blade, the fork end's opening would need to
    be nearly horizontal to allow the axle to slide out in response to brake torque.

    My opinion only- it's been 20 years since I had a bike with drum brakes.

    Jeff
     
  3. In article <[email protected]>, [email protected]
    (Chris Zacho "The Wheelman") wrote:

    > In the wake of the problems with the current front disk brake design and wheel ejection, the
    > question comes up, what about front drum brakes?
    >
    > Since these are entirely internal, I wouldn't think they would suffer the same problem, but do
    > they present a different one, due to any of their own possible design flaws? I'm not familiar with
    > front DB design (are they like the rear, as far as wheel/fork attachment goes?).

    How about the fact that drum brakes aren't very good? They're probably adequate for bicycle
    applications, but they aren't as fade-resistant as disc/rim brakes, and they make discs look light
    by comparison.

    Today, drum brakes survive as a preferred (as opposed to cheaper) vehicle braking on large,
    air-brake equipped trucks. I believe the issue there is an attempt to get more surface area for the
    brake, something that isn't an issue on a bicycle.

    Drums would be comparable to discs in their wet-weather utility, but otherwise seem to have few
    advantages for the application you're considering (solo bicycle).

    --
    Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club
     
  4. On Mon, 26 May 2003 22:12:46 -0400 (EDT), [email protected] (Chris Zacho "The Wheelman") wrote:

    >In the wake of the problems with the current front disk brake design and wheel ejection, the
    >question comes up, what about front drum brakes?
    >
    >Since these are entirely internal, I wouldn't think they would suffer the same problem, but do they
    >present a different one, due to any of their own possible design flaws? I'm not familiar with front
    >DB design (are they like the rear, as far as wheel/fork attachment goes?).
    >
    >Consider the following circumstances, no lawyer lips, and either a QR or a nutted axle. and thanks
    >for your response :-3)

    Do you even get drum brakes with QR? The ones I know of, Sturmey and their clones by Sachs and such,
    have a very long pin attached to the drum brake, which runs halfway up the fork and there fits into
    an attachment formed by brazing on a short box section.

    ah, here are pics: http://www.domme.ntu.ac.uk/mechdes/Research%20Interests/Ninterests%20article9.htm
    (or use http://tinyurl.com/crc6 )

    That lip on the end there fits into an attachment standard on forks designed for this kind of brake.
    These all use no lawyer lips and a nutted axle. Sometimes they may use the washers with a pin
    attached that fits into a hole in the fork. I would say there are a good 10 million of those (mostly
    Sturmey, and some of the compatible clone by Sachs) riding around in our teensy 16 million people
    country, varying from nearly new (Sturmey ended a few years back) to 40+ years old, and I've never
    heard of any issues.

    Jasper
     
  5. On Mon, 26 May 2003 23:50:22 -0700, Ryan Cousineau <[email protected]> wrote:

    >Drums would be comparable to discs in their wet-weather utility, but otherwise seem to have few
    >advantages for the application you're considering (solo bicycle).

    I'd say they're much better than discs for wet weather, and particularly for oily and gunky
    conditions. You never need to rub mud on a drum, as mentioned earlier in another thread for discs.

    Like I said, well over half the bikes here have Sturmey Archer drum brakes, and it's not just
    because it's traditional or cheap -- A Sturmey front hub nowadays costs $80 to replace (or next to
    nothing if you cannibalise an otherwise broken down bike), and it's always been more expensive than
    coasters or the cheap single pivot style rim brakes. Their ability to still brake nearly as well as
    they did when new 20 years on, without a single replacing of pads[1], should be amazing. For an
    all-weather, no-maintenance bike for getting around the place, no-hassle, I don't think you can
    beat them.

    Jasper

    [1] My mother's bike needed new pads at 25 years.
     
  6. I have put about 4,000 miles on a drum braked bike in the last year and a half. The bike has nuts on
    the front, rather than a QR. There have been no problems of any kind.

    I don't like the term "design flaw." Everything in the world has strengths and weaknesses. Drums
    have good and bad points and their suitability depends upon the application. They don't give the
    leverage that rim brakes give, and this means that you have to squeeze harder. They are heavy,
    something that may or may not matter to you. I have not had a brake fade problem, but I suspect that
    this would be an issue in very hilly terrain. They are definitely superior in wet weather. If you
    ride in an area where the roads are heavily sanded, you are freed from the need for frequent pad and
    rim replacement.

    In my case, the reduced maintenance and good wet weather braking makes drums or disks the only
    alternatives I would consider. On the other hand. depending upon your priorities, you might find
    drums unsuitable.

    Paul
     
  7. Chris Zacho The Wheelman wrote:

    > In the wake of the problems with the current front disk brake design and wheel ejection, the
    > question comes up, what about front drum brakes?
    >
    > Since these are entirely internal, I wouldn't think they would suffer the same problem, but do
    > they present a different one, due to any of their own possible design flaws? I'm not familiar with
    > front DB design (are they like the rear, as far as wheel/fork attachment goes?).

    Disk brakes apply their reaction the caliper, well behind the fork blade, and fairly close
    to the axle.

    The line from the axle to the pad is roughly 2:00 to 2:30 o'clock (viewed from the left.)

    Drum brakes have a reaction arm that attaches to the inside middle of the fork blade, maybe
    12:45-1:00. This is closer to parallel to the axle slot.

    In addition, the reaction arm on a drum brake is considerably longer than the axle-shoe distance, so
    there's considerably less force applied to it for the same amount of braking torque.

    Thus, this is a non-issue for drum brakes.

    Sheldon "Different Drummer" Brown +----------------------------------+
    | What sane person could live in | this world and not be crazy? | --Ursula K. LeGuin |
    +----------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772
    FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com
     
  8. Jobst Brandt

    Jobst Brandt Guest

    Paul Hamilton writes:

    > I have put about 4,000 miles on a drum braked bike in the last year and a half. The bike has nuts
    > on the front, rather than a QR. There have been no problems of any kind.

    > I don't like the term "design flaw." Everything in the world has strengths and weaknesses. Drums
    > have good and bad points and their suitability depends upon the application. They don't give the
    > leverage that rim brakes give, and this means that you have to squeeze harder. They are heavy,
    > something that may or may not matter to you. I have not had a brake fade problem, but I suspect
    > that this would be an issue in very hilly terrain. They are definitely superior in wet weather. If
    > you ride in an area where the roads are heavily sanded, you are freed from the need for frequent
    > pad and rim replacement.

    The reason automotive brakes switched to discs from drums is not a power problem but a control
    problem. Drum brakes are non-linear in response. That means you cannot tell how much braking will
    result from a given pedal pressure because the drum brake is self energizing. The shoes are
    literally sucked into engagement and that is why it was common to have brakes completely lock after
    driving through a puddle.

    Disc brakes and their derivatives, bicycle rim brakes, have their action completely decoupled, pad
    application force acting at right angles to the brake force, unlike the drum brake where shoes move
    in-line with drum rotation. Disc brakes were developed on, and were essential to aircraft to prevent
    them from veering off runways on landing, because drum brakes on landing gears did not respond
    identically.

    > In my case, the reduced maintenance and good wet weather braking makes drums or disks the only
    > alternatives I would consider. On the other hand. depending upon your priorities, you might find
    > drums unsuitable.

    Trucks use drums because they can dissipate more power more easily and economically. Railroads, on
    the other hand, cannot used drums because they easily cause skids and skidding a railroad wheel
    causes a flat spot that is irreparable and gets worse with use. Besides, once a railroad wheel skids
    it floats on molten steel and will not stop sliding until the brake is fully released.

    Jobst Brandt [email protected] Palo Alto CA
     
  9. Java Man

    Java Man Guest

    In article <[email protected]>, [email protected] says...
    > The reason automotive brakes switched to discs from drums is not a power problem but a control
    > problem.

    I don't know what really drove auto manufacturers to go to disc brakes. But my recollection is that
    resistance to fade was the reason advertising and other public pronouncements gave for the decision
    to switch. Maybe that was just marketing?

    > Drum brakes are non-linear in response. That means you cannot tell how much braking will result
    > from a given pedal pressure because the drum brake is self energizing.

    . . . when the activating end of the brake shoe is the leading end. Otherwise it's the opposite.
    IIRC, the vast majority of front drum brakes employed leading/leading, creating a strong servo
    action, while most rear brakes had one leading and one trailing, since less servo action was
    considered desirable to prevent the more troublesome rear wheel lockup.

    Rick
     
  10. In article <[email protected]>, [email protected] wrote:

    > Paul Hamilton writes:
    >
    > > I have put about 4,000 miles on a drum braked bike in the last year and a half. The bike has
    > > nuts on the front, rather than a QR. There have been no problems of any kind.
    >
    > > I don't like the term "design flaw." Everything in the world has strengths and weaknesses. Drums
    > > have good and bad points and their suitability depends upon the application. They don't give the
    > > leverage that rim brakes give, and this means that you have to squeeze harder. They are heavy,
    > > something that may or may not matter to you. I have not had a brake fade problem, but I suspect
    > > that this would be an issue in very hilly terrain. They are definitely superior in wet weather.
    > > If you ride in an area where the roads are heavily sanded, you are freed from the need for
    > > frequent pad and rim replacement.
    >
    > The reason automotive brakes switched to discs from drums is not a power problem but a control
    > problem. Drum brakes are non-linear in response. That means you cannot tell how much braking will
    > result from a given pedal pressure because the drum brake is self energizing. The shoes are
    > literally sucked into engagement and that is why it was common to have brakes completely lock
    > after driving through a puddle.

    What about trailing-shoe designs? I haven't beem lucky enough to spend any time behind the wheel of
    a vehicle with 4-wheel drums, but my father owned a 1965 Pontiac Custom Sport with mirror-finish
    drums. They had no fade resistance, apparently because when the drum heats up, it can flare
    slightly, and as soon as that happens the shoe contact area drops off dramatically.

    I'm not sure if that's the mechanism (could it be just that the expanded drum no longer conforms to
    the curve worn onto the shoe?), but I'm quite sure that fade resistance is not as good as disc
    systems that fit in a similar space.

    --
    Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club
     
  11. Jobst Brandt

    Jobst Brandt Guest

    Rick who? writes:

    >> The reason automotive brakes switched to discs from drums is not a power problem but a control
    >> problem.

    > I don't know what really drove auto manufacturers to go to disc brakes. But my recollection is
    > that resistance to fade was the reason advertising and other public pronouncements gave for the
    > decision to switch. Maybe that was just marketing?

    I just told you or didn't you read it. I was in automotive engineering at Porsche KG when this
    transition was made and worked on the development. Our first disc brakes were inside calipers
    grasping a disc-ring held on the periphery by a cut away aluminum brake drum.

    >> Drum brakes are non-linear in response. That means you cannot tell how much braking will result
    >> from a given pedal pressure because the drum brake is self energizing.

    > ... when the activating end of the brake shoe is the leading end. Otherwise it's the opposite.

    No one would make a trailing shoe drum brake or even one with linear motion shoes, there being
    insufficient force to stop the car. It would require forces that could only be achieved with a
    strong servo system.

    > IIRC, the vast majority of front drum brakes employed leading/leading, creating a strong servo
    > action, while most rear brakes had one leading and one trailing, since less servo action was
    > considered desirable to prevent the more troublesome rear wheel lockup.

    That was only toward the end of the drum brake on large sedans before the use of power brakes was
    well developed. The poor response got worse and braking was a hazard when peak demand was used.
    Brake companies and sports and racing car manufacturers were aware of the advantages of disc but
    had no way of implementing them on cars. The development was slow and tedious, especially with many
    in the industry who feared change, people who believed there was no problem having never used a
    disk brake.

    Jobst Brandt [email protected] Palo Alto CA
     
  12. Jobst Brandt

    Jobst Brandt Guest

    Ryan Cousineau writes:

    >> The reason automotive brakes switched to discs from drums is not a power problem but a control
    >> problem. Drum brakes are non-linear in response. That means you cannot tell how much braking will
    >> result from a given pedal pressure because the drum brake is self energizing. The shoes are
    >> literally sucked into engagement and that is why it was common to have brakes completely lock
    >> after driving through a puddle.

    > What about trailing-shoe designs? I haven't been lucky enough to spend any time behind the wheel
    > of a vehicle with 4-wheel drums, but my father owned a 1965 Pontiac Custom Sport with
    > mirror-finish drums. They had no fade resistance, apparently because when the drum heats up, it
    > can flare slightly, and as soon as that happens the shoe contact area drops off dramatically.

    > I'm not sure if that's the mechanism (could it be just that the expanded drum no longer conforms
    > to the curve worn onto the shoe?), but I'm quite sure that fade resistance is not as good as disc
    > systems that fit in a similar space.

    The cause was brake pad material. With a large contact area that a pair of shoes had, they had to be
    fairly soft in order to generate enough drag to stop the car. Softer materials have low vapor
    pressures and outgas and melt at far lower temperatures that the friction material in disc brakes.
    Disc brakes have substantially smaller contact area and an even greater increase in contact pressure
    to make up for that. Today there are probably no disc brakes without power assist, the mechanism
    being so simple and well developed.

    Disc brakes on aircraft and racing cars have carbon discs and pads that operate at glowing
    temperatures and produce no brake dust, that ugly reddish-brown sludge that dirties front wheels of
    cars. Their brake wear debris is CO2, a pretty clean substance.

    Jobst Brandt [email protected] Palo Alto CA
     
  13. Java Man

    Java Man Guest

    In article <[email protected]>, [email protected] says...
    > Rick who? writes:
    >
    > >> The reason automotive brakes switched to discs from drums is not a power problem but a control
    > >> problem.
    >
    > > I don't know what really drove auto manufacturers to go to disc brakes. But my recollection is
    > > that resistance to fade was the reason advertising and other public pronouncements gave for the
    > > decision to switch. Maybe that was just marketing?
    >
    > I just told you or didn't you read it.

    I didn't mean to offend you, and I wasn't questioning the accuracy of your statement. I meant that I
    pretend no knowledge of the real reasons
    vs. the marketing reasons, not that I hadn't read your post.

    Are you saying that reducing brake fade was not one of the reasons disk brakes replaced drums?
    (Please forgive my ignorance--my questions are asked to increase my understanding, not to
    challenge you.)

    Rick
     
  14. In article <[email protected]>, [email protected] wrote:

    > Ryan Cousineau writes:
    >
    > >> The reason automotive brakes switched to discs from drums is not a power problem but a control
    > >> problem. Drum brakes are non-linear in response. That means you cannot tell how much braking
    > >> will result from a given pedal pressure because the drum brake is self energizing. The shoes
    > >> are literally sucked into engagement and that is why it was common to have brakes completely
    > >> lock after driving through a puddle.
    >
    > > What about trailing-shoe designs? I haven't been lucky enough to spend any time behind the wheel
    > > of a vehicle with 4-wheel drums, but my father owned a 1965 Pontiac Custom Sport with
    > > mirror-finish drums. They had no fade resistance, apparently because when the drum heats up, it
    > > can flare slightly, and as soon as that happens the shoe contact area drops off dramatically.
    >
    > > I'm not sure if that's the mechanism (could it be just that the expanded drum no longer conforms
    > > to the curve worn onto the shoe?), but I'm quite sure that fade resistance is not as good as
    > > disc systems that fit in a similar space.
    >
    > The cause was brake pad material. With a large contact area that a pair of shoes had, they had to
    > be fairly soft in order to generate enough drag to stop the car. Softer materials have low vapor
    > pressures and outgas and melt at far lower temperatures that the friction material in disc brakes.
    > Disc brakes have substantially smaller contact area and an even greater increase in contact
    > pressure to make up for that. Today there are probably no disc brakes without power assist, the
    > mechanism being so simple and well developed.

    On cars, sure. Motorcycles, much lighter than cars, have disproportionately huge brake systems (twin
    300+mm dia. rotors being common), and are limited (like bicycles) by geometry more than traction or
    brake capacity in simple braking tests. Like bicycles, the brakes are manual, but they typically use
    floating discs, presumably to minimize necessary pad clearance and maximize mechanical advantage.

    A quick study on the web suggests that American cars started using power discs in the sixties and
    stopped using manual discs in the seventies. I assume the Europeans were a bit ahead of this trend,
    but possibly some low-end (or manfully sporting; what did Porsche do?) Euromobiles were using manual
    discs for longer than that.

    Interesting point about drum pad material. Couldn't they use a harder pad material with power-assist
    brakes and just dial up the boost? Did drum distortion play no significant role in the drum brake
    fade issues?

    > Disc brakes on aircraft and racing cars have carbon discs and pads that operate at glowing
    > temperatures and produce no brake dust, that ugly reddish-brown sludge that dirties front wheels
    > of cars. Their brake wear debris is CO2, a pretty clean substance.

    I'm not so sure about that. I used to watch a lot of F1 races (carbon-carbon discs and pads) and
    sometimes when those front wheels came off in a pit stop, there would be a cloud of black dust
    puffing out, apparently from the brakes. Were the brakes just not up to temperature?

    --
    Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club
     
  15. Thanks. The question was one that I got over E-mail. I personally was not considering them.

    The person asking, BTW had a hybrid that used these as a wet weather back up to his V-brakes.

    May you have the wind at your back. And a really low gear for the hills! Chris

    Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner
     
  16. Jobst Brandt

    Jobst Brandt Guest

    Rick who? writes:

    >>>> The reason automotive brakes switched to discs from drums is not a power problem but a control
    >>>> problem.

    >>> I don't know what really drove auto manufacturers to go to disc brakes. But my recollection is
    >>> that resistance to fade was the reason advertising and other public pronouncements gave for the
    >>> decision to switch. Maybe that was just marketing?

    >> I just told you or didn't you read it.

    > I didn't mean to offend you, and I wasn't questioning the accuracy of your statement. I meant
    > that I pretend no knowledge of the real reasons vs. the marketing reasons, not that I hadn't read
    > your post.

    > Are you saying that reducing brake fade was not one of the reasons disk brakes replaced drums?
    > (Please forgive my ignorance--my questions are asked to increase my understanding, not to
    > challenge you.)

    The drum brake as a high performance passenger car brake was at its end, but the big Detroit mfg,s
    didn't want to face up to it and kept producing grabby double leading shoe brakes, with power assist
    mostly with insufficient cooling to match the friction materials. While they were making high
    temperature brake shoes, the sports car people were working on discs. With their PR, the American
    public was satisfied with the crummy brakes they had until mundane foreign sedans began to appear
    here with disc brakes in competition. The brake fade problem was generally cured by high temperature
    compounds but the non-linearity remained. Today, highway trucks use drum brakes that have excellent
    fade resistance but still have the control problem. That is why you often see long dual skid marks
    on roads. The driver cannot assess how hard to brake with drums, especially on trailers.

    Jobst Brandt [email protected] Palo Alto CA
     
  17. Jobst Brandt

    Jobst Brandt Guest

    Ryan Cousineau writes:

    > A quick study on the web suggests that American cars started using power discs in the sixties and
    > stopped using manual discs in the seventies. I assume the Europeans were a bit ahead of this
    > trend, but possibly some low-end (or manfully sporting; what did Porsche do?) Euromobiles were
    > using manual discs for longer than that.

    Th power brake requirement depends on the weight of the car. Early Porsche 356 disc were unassisted
    and worked well. They had pad retraction features that were soon scrapped. With pads in constant
    sliding, pedal free travel was reduced. Only later as the 911 came along did power brakes come into
    play. I was no longer there when that happened.

    > Interesting point about drum pad material. Couldn't they use a harder pad material with
    > power-assist brakes and just dial up the boost? Did drum distortion play no significant role in
    > the drum brake fade issues?

    That's what they did and it's still the case with truck drums.

    >> Disc brakes on aircraft and racing cars have carbon discs and pads that operate at glowing
    >> temperatures and produce no brake dust, that ugly reddish-brown sludge that dirties front wheels
    >> of cars. Their brake wear debris is CO2, a pretty clean substance.

    > I'm not so sure about that. I used to watch a lot of F1 races (carbon-carbon discs and pads) and
    > sometimes when those front wheels came off in a pit stop, there would be a cloud of black dust
    > puffing out, apparently from the brakes. Were the brakes just not up to temperature?

    As far as I have seen recently, and in air terminals, there is no significant brake debris dust
    left over. I'm sure there are other components in the pad material than pure carbon and that
    small component may be what causes some solid debris. My introduction to this was with disk
    drives with carbon as a wear layer on sliders and disks. (In the storage industry the word is
    spelled with a "k")

    All sorts of more durable and harder materials were used as wear layers and never worked. In an
    atmospheric test chamber, I found that carbon in a nitrogen atmosphere caused particles that reduced
    friction and destroyed the magnetic layer in time from particle contamination, just as hard
    materials did.

    If the chamber was purged with oxygen, friction went up as carbon particles oxidized and evaporated
    allowing large surface contact. A grad student instrumented the chamber to measure CO2 production
    for his thesis and proved that carbon on carbon, in disk drives, caused benign wear debris of CO2 in
    an air environment. In oxygen friction went excessively high and with no oxygen, friction dropped
    due to particles in the interface, finally damagining the magnetic layer.

    Jobst Brandt [email protected] Palo Alto CA
     
  18. Jobst Brandt

    Jobst Brandt Guest

    Ryan Cousineau writes:

    > A quick study on the web suggests that American cars started using power discs in the sixties and
    > stopped using manual discs in the seventies. I assume the Europeans were a bit ahead of this
    > trend, but possibly some low-end (or manfully sporting; what did Porsche do?) Euromobiles were
    > using manual discs for longer than that.

    The power brake requirement depends on the weight of the car. Early Porsche 356 disc were unassisted
    and worked well. They had pad retraction features that were soon scrapped. With pads in sliding in
    contact, pedal free-travel was reduced and the mechanical advantage could be increased. Only later,
    as the 911 came along, did power brakes become standard. I was no longer there when that happened.

    > Interesting point about drum pad material. Couldn't they use a harder pad material with
    > power-assist brakes and just dial up the boost? Did drum distortion play no significant role in
    > the drum brake fade issues?

    That's what they did and it's still the case with truck drums.

    >> Disc brakes on aircraft and racing cars have carbon discs and pads that operate at glowing
    >> temperatures and produce no brake dust, that ugly reddish-brown sludge that dirties front wheels
    >> of cars. Their brake wear debris is CO2, a pretty clean substance.

    > I'm not so sure about that. I used to watch a lot of F1 races (carbon-carbon discs and pads) and
    > sometimes when those front wheels came off in a pit stop, there would be a cloud of black dust
    > puffing out, apparently from the brakes. Were the brakes just not up to temperature?

    As far as I have seen recently, and in air terminals, there is no significant brake dust debris. I'm
    sure there are other components in the pad material than pure carbon and that small component may be
    what causes some solid debris. My introduction to this was with disk drives with carbon as a wear
    layer on both sliders and disks. (In the storage industry disc is spelled with a "k")

    All sorts of more durable and harder materials were used as wear layers and never worked. In an
    atmospheric test chamber, I found that carbon in a pure nitrogen atmosphere generated particles that
    reduced friction and destroyed the magnetic layer in time from particle contamination, just as hard
    materials did. These particles are in the several tens of nanometers in size.

    If the chamber was purged with oxygen, friction increased as carbon particles oxidized and
    evaporated allowing large surface contact. A grad student instrumented the chamber to measure CO2
    production for his thesis and proved that carbon on carbon, in disk drives, caused benign wear
    debris of CO2 in an air environment. In oxygen friction went excessively high and with no oxygen,
    friction dropped from excess particle generation in the interface, ultimately damaging the
    recording medium.

    Jobst Brandt [email protected] Palo Alto CA
     
  19. Java Man

    Java Man Guest

    In article <[email protected]>, [email protected] says...
    >
    > The drum brake as a high performance passenger car brake was at its end, but the big Detroit mfg,s
    > didn't want to face up to it and kept producing grabby double leading shoe brakes, with power
    > assist mostly with insufficient cooling to match the friction materials. While they were making
    > high temperature brake shoes, the sports car people were working on discs. With their PR, the
    > American public was satisfied with the crummy brakes they had until mundane foreign sedans began
    > to appear here with disc brakes in competition. The brake fade problem was generally cured by high
    > temperature compounds but the non-linearity remained. Today, highway trucks use drum brakes that
    > have excellent fade resistance but still have the control problem. That is why you often see long
    > dual skid marks on roads. The driver cannot assess how hard to brake with drums, especially on
    > trailers.
    >
    Thanks.

    Rick
     
  20. On Wed, 28 May 2003 03:02:48 GMT, [email protected] wrote:

    >My introduction to this was with disk drives with carbon as a wear layer on sliders and disks. (In
    >the storage industry the word is spelled with a "k")

    Except for optical storage, which are discs. This of course lets the question remain: what do you
    call a magneto-optical? Disk or disc? Or both: disck?

    Jasper
     
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