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 Brake Safety Week was September 13-19, but anytime is the right time to review some brake safety basics. After all, law enforcement reports that brakes still make up the largest percentage of Out-of-Service violations cited during their 3 million roadside inspections. Let’s start with the CDL air brake check. You:
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| 1. |
Chock the wheels and then start the engine. |
| 2. |
Let the air pressure build to maximum pressure; watch the pressure gauge needle or needles (if dual system) – the low pressure warning light should not be on. |
| 3. |
When engine is at operating RPM, |
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| a. |
Check the pressure build up rate – it should build from 85 to 100 psi within 45 seconds in dual systems (unless vehicle has larger than minimum air tanks, if so, build up time may be longer). Note: If vehicle is older than 1975, pressure should build from 50 to 90 psi within 3 minutes with an engine idle speed of 600-900 RPMs. If air pressure doesn’t build up fast enough, have system repaired. |
| b. |
At a fast idle, determine if the air governor cuts off the air compressor at about the manufacturer’s specified cut off pressure (the air pressure shown on the gauge should stop rising); then step on and off the brake to reduce pressure, and see if the compressor cuts in at the specified cut in pressure. |
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| 4. |
When the air system is full charged (110-125 psi), shut engine off and urn on electrical power. |
| 5. |
Release both brake valves – push in parking brake yellow knob and service brake red knob. |
| 6. |
Depress the brake pedal to reduce air tank pressure. |
| 7. |
Then time the air pressure drop (the rate should be less than 2 psi in1 minute in single vehicles and less than 3 psi in 1 minute for combination vehicles); then apply 90 psi or more with the brake pedal, if after the initial pressure drop, the air pressure falls more than 3 psi in 1 minutes for single vehicles and more than 4 psi for combination vehicles, the air loss is too much. |
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Listen for an audible air leak; look to see if the pressure needle(s) fall(s). |
| 9. |
Note if the pressure warning light and buzzer come on before pressure drops to less than 60 psi in the air tank or the tank with the lowest air pressure in dual air systems. |
| 10. |
Watch to see if the parking brake knob pops out when the air pressure drops below the manufacturer’s specifications (generally between 20 and 40 psi). |
| 11. |
If a leak is detected, have the system repaired. |
| 12. |
If all is well, un-chock the wheels, turn on the engine, put the parking brake on (pull out yellow knob), and gently pull against it in a low gear to test that the parking brake will hold. |
| 13. |
While engine is still running and air pressure is normal, release parking break, move the vehicle forward slowly (about 5 mph) and apply the brakes firmly (depressing the brake pedal). Note if the vehicle is pulling to one side, feels unusual or there is a delayed stopping action. If so, have the brakes repaired. |
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In addition, if the air compressor is belt driven, you will want to check (or have the company’s designated individual check) the condition and tightness of the belt. Have slack adjusters tested; and make sure brake drums or discs, linings and hoses are in good working repair.
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