Why is Air Brake Testing Important for Truckers?

To look at a big rig, you’d never guess that a vehicle with that size and weight can merge, turn, and maintain smooth driving control at highway speeds, but the unique skills that truckers have make all of that possible so America can keep running.

Part of acquiring a Commercial Driver’s License (CDL) means getting tested on air brakes so every new driver gets on the road knowing exactly how a heavy-duty vehicle’s complicated air brake system works. But even after you get your CDL, you should still brush up on your air brake knowledge and skills because you never know where you’ll end up during delivery and in what weather conditions. Whether you’re reviewing the necessary skills for CDL air brake testing or just wanting to brush up, here’s a nine-step air brake test to keep you confident on the road.

The 9-Step CDL Air Brake Test

  1. Static Air Leakage. Turn off the engine with a fully-charged air system. Then, release the parking brake and time the air pressure drop. After the initial air loss, the loss rate should not be greater than two PSI in one minute.


  1. Service Brake Air Leakage. With the engine off, apply the service brake firmly to 90 pounds and hold it steady. After the initial drop, the pressure should drop no more than three PSI in one minute.


  1. Low Air Warning System Check. Keeping the engine off and electrical on, step on the brake pedal repeatedly to fan off the air pressure. Listen for the audible buzzer and watch for the visual warning light.


  1. Spring Brake Valve Check. Continuing to fan off the air pressure with the brake pedal and the engine off, check for the tractor protection valve closing at 20-40 pounds.


  1. Air Pressure Recovery Check. Start the engine and raise to operating RPMs or high idle. Check that the pressure builds from 85-100 pounds within 45 seconds.

Air brake components


  1. Governor Cut Out Check. Maintaining your high idle, check the governor cut-out at between 120-130 pounds.


  1. Governor Cut In Check. Keeping the engine on, pump the service brake to reduce air pressure to around 90-100 pounds and check the compressor cut-in/air pressure rise.


  1. Spring Brake Test. With the parking brake on (removing the wheel chocks), engage a low gear and gently pull against the parking brake to test the hold.


  1. Service Brakes. Engine on, wait for normal air pressure and release the parking brake. Move ahead to a speed of about 5 mph, then firmly apply the service brake. Observe if the vehicle pulls to one side, has an unusual feel, or has a delayed stopping action.

Where to Buy New Air Brake Components

Of course, testing your air brake system is a lot easier when all your parts and components are at peak performance. Whether you need new valves, sensors, or other critical air brake components, Match Made Parts are designed to drive value while providing the quality and performance you need from your heavy-duty parts.

Match Made is now a complete solution across 12 parts categories for all of your trucking needs including shocks, rotating electric, lighting, and more. Check out our full haul of heavy-duty everything and discover the difference with Match Made.