Heavy duty trucks have special braking needs, which require the use of air brakes. Air brakes operate using a belt driven compressor to keep a constant pressure in a set of air accumulators. This pressure is approximately 115 to 120 pounds per square inch. These types of systems are more complex and harder to maintain. There are a variety of problems that can arise with air brake systems. These are the two most common:
This guide will instruct the reader on how to trace the causes of these problems and repair them.
Care must be taken in all phases of repair, since, unlike hydraulic brake systems, air brakes maintain air pressure even without the brakes applied.
This is a condition that can have a couple of causes. The main case is usually a binding condition in the brake chamber. The brake chamber is a sealed air chamber with a rubber diaphragm with a steel push rod in the middle of it, which actuates the brakes when the pedal is pushed. There is a spring to force the rod back to the relaxed or inactivated position. This spring will occasionally bind and cause the brakes to either stick against the drum or not fully retract. Care must be taken when repairing this, as the system is under pressure and the spring is high tension.
Air pressure acts in a similar fashion as the power brake booster in a passenger car or light truck. This action makes it so that normal braking action will not require massive amounts of pedal pressure to stop the vehicle. If your vehicle is requiring more pedal pressure than normal, this will usually mean that the system is not building air pressure in the accumulators.
If prudent care is taken during these repairs to follow these instructions, you can safely undertake basic repairs to your heavy duty vehicle’s air brakes.