LRO: RE: Graphite in brakes

From: Lee Jones (leejones6@home.com)
Date: Mon Jun 04 2001 - 09:13:47 EDT

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    This thread has my mind messed up - back in the 60's and early 70's, on our
    street cars (and on the race cars too!) we used to put four or five lead
    pencil inserts in the friction surface of the pad, not on the edge, to cut
    down on the squeal (and on the race car - a Mini Cooper to cut down on
    having the pad weld itself to the rotor).

    Putting the lead in the edge of the pad would seem to me to be totally
    harmless until the pad wears down to the level of the graphite and then you
    would have a solid line (or lines) of graphite all across the pad (or shoe)
    surface. Earlier someone wrote that the graphite would act as a lubricant
    (which it didn't seem to in any way) if placed in the wear surface of the
    pad. My understanding was that - at least - disk brakes work mechanically
    more than as a friction material against the rotor (yes if oil gets in there
    it WILL degrade the braking effect) and that much of the feeling of brake
    fade was in gasses that were generated between the pad and rotor when the
    brakes were very hot. The pads on the race car were mostly made out of
    sintered iron which still worked good when the brakes were hot but would
    both boil the brake fluid and would weld themselves to the rotor when the
    car was stopped.

    Lee

    -----Original Message-----
    From: owner-lro@works.team.net [mailto:owner-lro@works.team.net]On
    Behalf Of RON WARD
    Sent: Monday, June 04, 2001 8:45 AM
    To: lro@works.team.net
    Subject: LRO: Graphite in brakes

    It worked like a dream on my 1995 RR (Rangie, not Rolls) Classic. I used
    Berol / Turquoise No. 12 Drawing Leads that I keep a supply of for a
    drafting pencil that I used in college. The leads are 5 inches long,
    pointed at one end and roughly 1/8" in size. I drilled four 1/8" holes
    about 3 inches into the surface of the leading edge of every pad on the
    truck. No squeaking this morning and I suppose as the pads continue to
    wear, exposing the graphite, no squeaking will ever happen.

    Thanks

    >>> Marin.Faure@PSS.Boeing.com 06/01/01 08:29PM >>>
    Date: Fri, 1 Jun 2001 08:43:38 +0100
    From: "Steve Mace" <steve@solwise.co.uk>
    Subject: Re: LRO: RE: Asbestos (was tuning by eye)

    On 31 May 2001, at 10:36, Faure, Marin wrote:

    >> Actually, the graphite does not do anything to lubricate the lining. The
    > purpose of the lead "inserts" in the edge of the lining (not the face) is
    to
    > dampen the high-frequency vibrations that are the actual source of the
    squeal.
    > It works for both pads and shoes.

    >Presumably under the assumption that a couple of inches of pencil lead is
    going to alter the mass of the pad/shoe enough to actually alter it's
    vibration
    characteristics?

    I'm not going to dispute your numbers, but the vibration dampening effect is
    what ROLLS ROYCE said about the technique in a description of it that I
    read many years ago. I first read about the lead thing in the early 1970s,
    so the technique has been around at least that long. (The same RR pamphlet
    I
    read also described a technique for limo drivers to come to a stop without
    causing the vehicle to rock back slightly, thus avoiding "disturbing" the
    occupants in
    back.) There was an sketch of the lead thing, and the holes were drilled
    in the edge of the lining on the shoe, NOT in the face of the shoe.)
    As I recall, the Rolls Royce pamphlet did not describe the technique as a
    way of
    overcoming the problems of asbestos-free brake lining, but simply as a way
    to
    eliminate brake squeal if you had it. Makes sense, as they were still using
    asbestos in brakes in the early '70s.

    Over the years, I've had the technique described to me by a few mechanics,
    and
    they all said the same thing- drill the holes in the edge of the lining
    material
    parallel and as close to the backing plate as practical. Then insert the
    lead
    cores, which effectively break up the vibration patters. The length of the
    cores should be as long as you can get away with. I use pieces about 3
    inches
    inches long on our Range Rover, and I put in four of them in each pad. The
    vehicle had a bad squealing problem at low speeds from day one, but I kept
    putting
    off doing the lead thing until recently. When I reinstalled the pads, the
    squeal was
    gone, and so far it's not come back.

    As for dampening vibration, if you give a tuning fork a whack, you can
    almost
    completely stop the sound by touching it with a just a feather. So I'm not
    sure
    mass is the only factor affecting the interruption of high frequencies,
    which is
    what brake squeal is.

    But what I know about physics wouldn't fill a thimble, so I can't make any
    sort of
    scientific argument supporting the technique as described by Rolls Royce and
    the
    mechanics I've talked to. All I know is that following their process, brake
    squeal
    goes away. I would assume that if you drilled holes in the face of the pad
    or shoe,
    you'd accomplish the same thing for the same reason.
    ___________________________
    C. Marin Faure
      (original owner)
      1973 Land Rover Series III-88
      1991 Range Rover Vogue SE
      Seattle



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