A: I drilled near the outer edge of my drums (on the vertical face) so air can pass through near the hottest part and keep my drums from warping. From: Tom Jennings <tomj@xxxxxxx> Subject: Re: [Amc-list] Re; Drilling brake drums. To: "AMC/Rambler owners, drivers and fans." <amc-list@xxxxxxxxxxxx> Message-ID: <Pine.LNX.4.64.0702182336220.26520@xxxxxxxxxxxx> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed On Sun, 18 Feb 2007, John Elle wrote: >I did a little web searching on this subject too and it comes back to me >as a mixed review. The technical answers seem to support that it is a >waste of time and money. Well I don't think it's billed as a revolution, only an incremental improvement. It's an old trick, I assume it predates simple junkyard-parts disc brake swaps. There may be hard braking/hot shoe outgassing improvements, but I'm with you, they have got to be minimal, esp. with modern linings. The holes as I recall are 1/8" or so, and a dozen of them sweeping across the linings isn't going to improve braking much. Where *I* think they will improve things is in cooling off hot drums. Centrigugal force "should" pump air out the holes, right where it will be hottest. There's air intake at the backing plate/drum flange area. I bet it does improve wet-brake drying too. But mainly, it's an old-timey fixup for old brake systems. Swapping in discs has got to beat it 5 times over though, bang-per-buck. >As far as drum brakes failing due to heat, that was a typical failure >mode and I have experienced that too. It was always my understanding >that heat caused the drum to expand thus reaching a point where the >travel supplied by the wheel cylinder was exceeded so the wheel >cylinders capability of supplying pressure to the brake shoes was >greatly reduced. Even under the condition of over heated, they did not >get anywhere near the temperature of a disc brake assembly that was >working normally or even hard. I dunno -- in my and everyone's experience, whatever the mechanism, one really hard, fast stop from high speed sure took "adequate" size front drum brakes out of commission for quite some time! When drums get hot they "bell" -- hot metal expands a lot. The flat face of the drum keeps it more or less the same diameter as cold, but the outer edge -- along the backing plate -- gets larger. Some braking force gets wasted pushing shoes sideways. When a disc rotor gets really hot, it gets slightly larger diameter (no effect) and slightly thicker (pushes against the pads! I doubt anything usefully measurable). But they don't change geometry. Also, hollowed discs pump cool air like mad from the center out through the edges. Disks beat drums at everything except pedal force (drum shoes self-servoing) and looking retro :-) _________________________________________________________________ Refi Now: Rates near 39yr lows! $430,000 Mortgage for $1,399/mo - Calculate new payment http://www.lowermybills.com/lre/index.jsp?sourceid=lmb-9632-17727&moid=7581 _______________________________________________ Amc-list mailing list Amc-list@xxxxxxxxxxxx http://www.amc-list.com/mailman/listinfo/amc-list