By making a heavy service brake application while the spring brakes are applied. This adding together of the two forces can potentially cause damage to slack adjusters, s-cams, brake chambers, brake shoes, and brake drums.
Yet, this problem is now obsolete – the majority of trucks are equipped with an anti-compounding valve. This valve prevents the service brakes from being applied if the spring parking brakes are engaged.
Despite this advance in technology, a significant number of driving instructors are going to get “right torqued” if a students makes a heavy service brake application and the spring parking brakes are engaged!