Drum Brake Automatic Adjuster

On duo-servo design brakes, the adjuster uses movement of rear (secondary) shoe during reverse brake application to turn brake adjusting screw. Screw is rotated a small amount to maintain proper lining-to-drum clearance.

Non-servo design brakes use an incremental adjuster that adjusts during braking whenever a wear gap appears sufficient to actuate the adjuster wheel. Brake adjustment occurs during forward and rearward braking.