Cam 1 turns about fixed axis A and has working surface b which slides along flat surfaces a of shoes 2. Shoes 2 turn about fixed axis B. When cam 1 is turned, shoes 2 are spread and forced against the inner surface of drum 4. Spring 3 tends to retract the shoes and release the brake. I t also holds shoes 2 in contact with cam 1. Cam 1 has four separate working surfaces. If it is turned 90° so that the flat surfaces are between the shoes, the brake will remain in the applied position.
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