Heat temper brake pads
Mike Arman
Armanmik at earthlink.net
Fri Nov 14 14:24:10 PST 2008
Mark R wrote:
> Mike,
>
> I have a wholesale account with a big east coast tool distributor. The
> problem is that whenever I place an order, I end up spending WAY too
> much money on personal tools... so I feel your pain! $4.00 book with
> some good tips... sounds like a "score" to me!
>
I've gotten a LOT of great tech books this way. Streety & Licthter, Principals of the Internal
Combustion Engine, 1928 no less and still VERY pertinent. $2 or so. Jan Norbye's book on the Wankel
engine, There's a Hercules Wankel bike in the garage. $5 for that book - lots, lots more, too many
more! Piles, heaps, mounds of aircraft stuff - F5E POH, $3.! ("try this, try this, eject."), others,
too. Having ERAU in town helps - lots of students dump their texts (fools) and many retired military
get rid of their stuff too.
Bought a trunkload of aircraft tools from a retired Eastern Airlines A&P - FILLED the trunk on my
V8Q, a fat $200 for all. Clecos? Do I have clecos? Gawd, do I have clecos!
> Baking pads would work to burn off organics (greases, oils) and you'd
> want to be near the top of a toaster oven's range (375-400 degrees F,
> give or take) for 20-30 min. Of course, this may or may not leave toxic
> residue in your toaster oven. =)
> Oh, and backing plate paint would probably start to burn off, especially
> on a street pad.
>
> OK, so this might be a good way to "break-in" a set of pads.... but the
> racers and technical folks among us call the necessary process something
> else. "Bedding in the pads."
>
> A critical part of the bedding in process is to heat up the pads enough
> to burn off things (organics, binding compounds, etc.), but that's only
> 1/2 of what's going on at the pad. On a more minute level, I'm told the
> friction material is softer during this process which allows for two things:
> 1. Directional alignment on a molecular level (which may or may be
> bogus... I've never seen electron microscope scans to prove this out).
> 2. Increased pad wear to match the pads to the rotors (high spots are
> quickly worn away so that there is even braking force between the pads
> and rotor as wall as maximizing the available surface area).
>
> I do know that some pad manufacturers have had verbiage about only
> putting pads back onto their first installed position (no flipping
> in/out, axles, or left/right). I have no idea if this is due to even
> wear with the rotor (likely), or the possibility there is in fact some
> form of molecular alignment increasing the bonding of the friction material.
>
> The other critical side of the equation is what's going on at the
> rotor. At the rotor, some material is embedded into the face of the
> rotor and increases the coefficient of friction. This is "bedding in"
> as pad material is evenly deposited to the rotor face. Baking the pads
> before hand might preclude this process from occurring. I see faint pad
> outlines on rotor faces frequently. Localized transfer has occurred,
> causing a hard, high spot. With sensitive brake systems, you can
> actually feel it in the pedal as a pulsation. The pad face temperatures
> when bedding in (even for a street pad) would exceed a household oven's
> temperature. My track pads aren't supposed to lose their friction until
> 1250 degrees F (that's face temp, not backing plate or caliper temps).
>
> I can see a few situations for baking a pad in an oven.
> 1. Where bedding in is impractical or dangerous (like on an airplane
> where there's not enough runway to safely heat up the brakes).
Bingo . . . !
Cessna with fresh engine and new brakes (and a bunch of other new stuff).
Problem is I shouldn't be running the fresh engine on the ground to bed in the brakes, and I'm not
wild over the idea of going flying (recommended break-in procedure for the engine) and landing with
not much in the way of brakes. I think that's what will happen, though - I have a 3,000 foot long
grass strip to work out of, so wonderfully effective brakes are not the top priority, keeping the
nosewheel off the ground for as long as possible (normal landing, doubly good procedure for grass
strips) slows the airplane down very well anyway - but you know this already ;-)
I'd just like to hedge my bets - I do have an old toaster oven, and if I can find out "how hot", I
might as well do it!
Sounds like it will be 1 hour at 200 degrees, followed by 4 hours at 450 degrees, and a gentle
cooldown overnight. Then sell the toaster oven at a thrift store . . .
> 2. Where rotors preclude normal bedding in processes due to their
> coatings. ATE slotted rotors come to mind since I've installed a bunch
> of those, including on my Escalade EXT and my mother's BMW 330ix.
> 3. Decontamination.
>
> Make sense? Anyone else has thoughts or experience on the subject?
>
> Mark Rosenkrantz
> PA-28R-200 based at CZG, Endicott, NY (so I've not purchased Mike's book
> on C-150s, yet).
Phooey - you blew my cover. (but I can live with that!)
Best,
Mike
N150EM
> A few Audis. a trailer, and a few American vehicles.
>
>
>
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