Drum brake wear indicator

摘要

A wear indicator for the friction material of a drum brake shoe includes a spring-loaded captive plunger carried in an elongated sleeve attached to the brake shoe. The plunger includes an enlarged head which abuts the sleeve and which is recessed below the surface of the unworn friction material at a depth which corresponds to a worn-out shoe. When the shoe wears to a sufficient degree, the plunger head is worn off by the rotating brake drum and the plunger is released. When freed, the plunger is moved by the spring bias and slides within the sleeve to press against an electrical contact carried by the backing plate of the brake to close an alarm circuit.