RECONDITIONING BRAKE DRUMS AND SHOESDRUM BRAKESINSPECTION OF DRUMSThe friction surface of brake drums must be smooth, trueand concentric. Make certain with a visual check thatdrums are not barrel shaped, bellmouthed, scored oreccentric.Hard or chill spots, Figure 1, in brake drum may producepedal pulsation and roughness or brake surge. If theseeffects are present, drum should be replaced.Figure 1 - Hard or Chill Spotted DrumA barrel shaped drum (Figure 2) results fromoverheating. If this barrel shaped condition is notcorrected, the braking surface is reduced and unevenlining wear results.Figure 2 - Barrel Shaped DrumExtreme pressure which over a period of time will createa bellmouthed drum as shown in Figure 3. Brake liningson a bellmouthed brake drum will make contact only onthe inner surface of the drum. In addition to cutting thebraking surface to a minimum, it will also cause unevenand rapid wear.Figure 3 - Bellmouthed DrumScored drums are the result of worn linings to the pointwhere the drum-to-shoe contact is made or anaccumulation of small steel particles imbed themselvesin the brake lining (Figure 4). The steel particles form atough scale which is sometimes harder than the drum.As a result, deep grooves are formed in friction surfaceof drum.Figure 4 - Scored DrumBrake drum scoring never improves but continually getsworse until both lining and brake drum are useless.Attempting to reline brakes without turning scored brakedrum surface will quickly destroy new lining and makeeffective braking impossible.Check inner side of drum surface for tool marks todetermine if drum has been previously reconditioned,Figure 5. If so, an oversize lining may be required.Figure 5 - Check Brake Drum for Tool MarksCTS-4082B - Page 3
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