Air chamber push rod action forces a wedge-shaped push rod between the brake shoe rollers. This forces the brake shoe lining against the brake drum. Each wheel may be equipped with one or two chambers, depending on vehicle size and style.
These brakes may be equipped with a self-adjusting mechanism or a manual star wheel adjuster. The star wheel adjustment is made with the vehicle jacked up, to ensure that the brake linings do not drag. Manual adjustment of wedge-type brakes is usually a job for a mechanic.