When the brakes are applied, circuits send compressed air from the storage tanks to front and rear service chambers that push the brake shoes into the brake drums, thus slowing down the vehicle. Semis ...

Failing air chambers provide little warning of the trouble looming within. Their demise is usually sudden, accompanied by the agonizing sound of escaping air as the parts exhale for the last time.

Have you ever tried to back up an 18-wheeler? It's no small feat, but once you understand how air brakes in semi trucks work, it all starts to make sense.