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How to Perform a DOT Brake Test

Commercial trucks drivers, from time to time, are stopped by the Department of Transportation (DOT) and asked to perform an air brake test to assure maximum safety of the braking system. The purpose of the inspection is to make sure the brakes do not leak, that the slack adjusters are adjusted properly and that the brakes are balanced in the front and back. For safety purposes, when you test the brakes, the DOT will allow a maximum loss of 4 psi, although mechanics agree that 8 psi is acceptable.

Exit your vehicle when prompted by the DOT official, and chock your wheels with your wheel chocks. Make sure you place one at the front of the truck, in front of the tire and once at the back of the truck, behind the tire. This is to prevent the truck from rolling.

Enter the vehicle on the driver side, and locate the red and yellow knobs on your dash; push in both knobs to avoid compounding your braking system.

Depress your brake pedal, and release the pedal. Depress the pedal again, and hold it down for 1 minute. Look at the two gauges for the front and rear air brakes on the left-hand side of your dash. Make sure both gauges show fully stroked brakes. The front should read 60 psi and the back 120 psi. The brakes should not lose more than 4 PSI when holding the brake pedal down for 1 minute.

Release your brakes by lifting up your foot off the pedal. Depress and release the brake pedal two more times to adjust the slacks adjusters. This is part of the DOT requirements; make sure you do not forget to do this.

Tip

You should perform the air brake test every day before driving your vehicle, not just when asked by the DOT. This is to ensure you keep your brakes in proper working condition, that the air cables are hooked up properly and that the brakes provide maximum safety on the highway.

Warning

If you are stopped by the DOT and fail to perform the brake test properly or the system loses more than 4 PSI, you might be liable to a ticket with fines ranging from $250 to $500 or more.