You've seen it time and again: the job-site truck driver who stops for nothing. Could be it's just a sign that his haul truck needs a brake job, or that the last one wasn't done properly.Because efficient braking takes place only when lining material meets drum walls correctly, shop personnel can help heavy-duty-truck operators stop when and where they plan to by focusing on two components in the brake system: drums and brake-shoeassemblies. Everything else in the system exists only to make that meeting possible and proportional.At first glance, brake drums seem unsophisticated. Consider what's asked of them, though: Thanks to advances in gear trains, aerodynamics and the reduction of rolling resistance, the braking power required to maintain a 50-mph speed down a 3.5-percentslope with an 80,000-pound load has more than doubled since 1974. The action of braking converts kinetic motion into heat-and that heat is dissipated by the brake drums.A job description like that demands advanced metallurgy and sophisticated machining. Drum walls need to withstand braking forces, dissipate heat and break in linings so the entire lining surface rubs the drum evenly.
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