The British Columbia Driving Commercial Vehicles Manual recommends two different methods: 1. Make a mark on the pushrod where it exits the brake chamber, and see how far it moves from the brake chamber when the brakes are applied. 2. Measure the length of the part of the pushrod from the brake chamber to the clevis pin, and see how much it increases when the brakes are applied. Either method may require two people: one to apply the brakes, and one to make the appropriate measurements before and after the brakes are applied. Note: There are also various pushrod stroke measuring tools available commercially.