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Well, OK, but that analogy seems flawed in that the VCR was a very new and complex technology. I meant to say that this brake question exists precisely because discs seem quite the opposite: WAAY simpler construction, lighter weight, and both were first applied to cars about the same ancient time (~1902, drums on Renault, discs by Lanchester). This link ( http://web.bryant.edu/~ehu/h364proj/sprg_97/dirksen/brakes.html ) suggests that it was indeed the lack of reliable boost that limited disc acceptance; but that would hardly explain why so many cars still have drums at the rear, even today! A clue or two may be hidden in the otherwise very nice history of car brakes at ( http://www.motorera.com/history/hist07.htm ), where the comments are made that external-surface brakes suffer from ingestion of road dirt and debris; that the Lanchester brake screeched until modified to asbestos linings; and that the early brakes wore quickly. That is, maybe discs just didn't hold up until almost all roads were paved with asphalt or concrete, reducing the presence of gravel (loose or in tarmac); and until friction materials were found strong enough to bear up while operating in the open with comparatively small pad areas (disc pads being ~1/2 the face area of a typical drum). I also suspect there is some fine metallurgy required to make a flat disc that won't warp when heated red-hot, then clamped in one sector to cool (say, at a traffic light) - I know I've warped a few over the years. Bottom line guess: drums remained long after discs were cheaper to build and better in most operation; because the warranty rates were high enough to offset the initial savings - and that this penalty still exists for back ones that bear the grip of parking brakes, so cheaper cars still use back drums. jc On Dec 9, 2007, at 8:18 PM, Kenyon Wills wrote:
John Corey CFIC-Qdrive, 302 Tenth St., Troy, NY 12180 USA 518-272-3565 x201 fax: -272-3582 |
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