For good braking action the brake drum should be

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  • josephwanjala
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For good braking action, the brake drum should be perfectly round and have a uniform surface. Brake drums become out-of-round from pressure exerted by brake shoes and from heat developed by application of the brakes. The brake drum surface becomes scored when it is worn by braking action. When the braking surface is scored or the brake drum is out-of-round, it may be necessary to machine the brake drum until it is smooth and true again. Care must be taken not to exceed the maximum allowable diameter according to the manufacturer's specification. Each drum is stamped with the maximum diameter information and, if exceeded, it should be discarded and replaced with a new one. 1.3.1.6 Brake Shoe Adjusters Brake shoe adjusters maintain correct drum-to-lining clearance, as the brake linings wear. When the brake lining clearance to drum ratio is too great, the adjuster will move the brake shoe closer to the drum for improved braking. The common device used for automatic adjustment is the star wheel. The star wheel is turned by an automatic adjuster that normally functions when the brakes are applied with the vehicle moving in reverse. If there is too much lining clearance, the brake shoes move outward and rotate with the drum enough to operate the adjusting lever. This lengthens the adjusting mechanism, and the linings are moved closer to the brake drum, thereby maintaining the correct lining-to-drum clearance. The star wheel brake shoe adjusting mechanism consists of a star wheel (adjusting screw assembly), adjuster lever, adjuster spring, and an adjusting mechanism. The adjustment mechanism system may consist of the one of the following type: a cable, a link or lever: 1.3.1.6.1 Cable Type The cable type self-adjusting system uses a braided steel cable and the expanding action of both brake shoes to accomplish the self-adjusting action in forward and reverse directions (Figure 13-9 View A). A one-piece cable is attached to the adjusting lever and passes through a cable guide on the primary shoe. The cable then is passed up and over the anchor and attached to the secondary shoe. Operation is as follows: 1. Brakes are applied and the shoes expand and contact the drum. 2. The primary shoe self-energizes, and, through servo action, applies the secondary shoe. 3. The heel of the secondary shoe is lodged against the anchor pin. 4. The movement of the primary shoe tightens the cable by shifting the cable guide outward and in the direction of rotation. 5. The cable then moves the adjusting lever upward. If enough shoe-to-drum clearance is available, the adjusting lever will engage the next tooth on the star wheel. The brake shoes retract and the cable’s tension is relaxed as the brakes are released. The return spring then helps force the adjusting lever downward, rotating the star wheel, which expands the brake shoes. In the reverse direction, the toe of the primary shoe is forced against the anchor, and the secondary shoe moves around to tighten the adjusting cable. The adjusting process is then completed. NAVEDTRA 14264A 13-13
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1.3.1.6.2 Link type
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  • Fall '19
  • pistons, Disc brake, Drum brake, Vehicle braking technologies, Brake springs, Hydraulic Brake System

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