Here is another example of a type of brake assembly used on some air brake equipped vehicles. The action of the brake chamber push rod forces a wedge shaped push rod between the brake shoe rollers. This forces the brake shoe lining against the brake drum.

The vehicle may be equipped with a single chamber or two chambers on each wheel, depending on the vehicle’s size and style.

These brakes may be equipped with a self-adjusting mechanism or with 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.

Spring brakes added to these units are of the piggy-back type.