Air brakes, sometimes called air-hydraulic brakes, are used on heavy trucks and locomotives. As the name implies, the air brake system uses compressed air as the operating force for stopping vehicles or equipment.
A foot pedal in the driver's cab activates a mechanism that opens pressurized air valves in each of the truck's axle groups, so they release their brake shoes. The driver then uses a hand brake to control additional air pressure and applies individual brake shoes in each axle group.
Most trucks have two service brakes: power-assisted or power-brakes that use engine vacuum and compressed air. A professional mechanic should check each brake system carefully before you pull any vehicle on the road.
A complete brake inspection should include a hydraulic brake test, a power-assist system check, and a DOT brake tire/caliper examination. We recommend that you have any grinding or squealing noise checked by a professional mechanic to determine if it is caused by an improperly adjusted brake shoe rubbing against the rotor or drum. If this is the case, then the brake shoe will need to be replaced.
Brake replacement includes rotors and drums, which are machined for flatness. If they are not flat, it will compromise your vehicle's braking capabilities because the brakes won't release properly. The mechanic should also check discs or pads for damage or defects that might cause the brakes to fail.
Mileage Recommendation: 40,000-50,000 miles
If your heavy-duty truck has a problem with the brakes, it can be repaired by bleeding the brake lines to get rid of the air, replacing brake pads and shoes, welding up the holes in drums or rotors, or fixing worn bearings. The cost for replacement work often depends upon the mileage of the vehicle.
Usually, heavy-duty trucks have brake drums and rotors that are made from cast iron. If they are not machined, there is a chance that the drum will crack if it overheats from being filed or ground down with an abrasive wheel. Sometimes cracks won't be visible until the mechanic uses a brake lathe machine to see cracks in the metal.