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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