Air Brakes Pre Trip Inspection


R and M Diesel Truck Brake Service
870-941-6160 Short drive from down town Little Rock, Arkansas.Close to I-30 and I-530.

The following items are a general listing of what is examined on a commercial diesel truck vehicle during roadside DOT inspections on a Brake System:

1. Any missing, broken or loose component.2. Audible air leaks.3. Exceeding adjustment limits.4. Cracked, loose, too thin or missing linings or pads.5. Wheel seal leaks.6. Hubcap leaks.7. Inoperative parking brake.8. Cracked or broken drum.9. Worn hoses or tubing.10. No low air warning at 55 psi and below.11. Inoperative or missing valves.12. Air compressor loose or defective mount.

Air Brake Check Pre Trip Inspection:

Air brake safety devices vary. However, this procedure is designed to see that any safety device operates correctly as air pressure drops from normal to a low air condition. For safety purposes, in areas where an incline is present, you will need to use wheel chocks during the air brake check. The proper procedures for inspecting the air brake system are as follows:

Test Air Leakage Rate (Static check)

With a fully-charged air system (typically 120 psi), turn off the engine, chock the wheels, release (push in) the parking brake button (all vehicles) and trailer air supply  button (for combination vehicles) and time the air pressure drop.
After the initial pressure drop, the loss rate should be no more than 2 psi in one minute for single vehicles and no more than 3 psi in one minute for combination vehicles.

Test Air Brake System for Leaks.

With parking brake, (all vehicles) and trailer air supply button (for combination vehicles) released (pushed in), apply firm pressure to the service brake pedal. Watch  the air supply gauge and listen for leaks. After the initial pressure drop, the loss rate for single vehicles should be no more than 3 psi in one minute and no more  than 4 psi in one minute for combination vehicles. If the air loss rate exceeds these figures, have the air system repaired before operating.

Test Low Pressure Warning Alarm and / or Signal.

Turn the key to the on position. Rapidly apply and release the service brake pedal to reduce air tank pressure. The low air pressure warning signal must come on  before the pressure drops to less than 60 psi in the air tank. If the warning alarm/signal doesn’t work, you could be losing air pressure without knowing it. This could  cause the spring brakes to activate suddenly. Only limited braking can be done before the spring brakes come on.

Check That the Spring Brakes Come on Automatically.

Continue to rapidly apply and release the service brake pedal to further reduce air tank pressure. The trailer air supply button (if it is a combination vehicle) and  parking brake button should pop out when the air pressure falls to the manufacturer’s specification (usually between 20 to 40 psi). This causes the spring brakes to  come on.

Check Rate of Air Pressure Buildup.

When the engine is operating at 1800 RPM, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. (If the vehicle has larger than  minimum air tanks, the buildup time can be longer and still be safe. Check the manufacturer’s specifications.) If air pressure does not build up fast enough, your  pressure may drop too low during driving, requiring an emergency stop. Don’t drive until you get the problem fixed.

Test Service Brakes.

Wait for normal air pressure, release the parking brake and trailer air supply button (for combination vehicles), move the vehicle forward slowly (about 5 mph), and apply the brakes firmly using the brake pedal. Note any vehicle “pulling” to one side,  unusual feel, or delayed stopping action. This test may show you problems which you otherwise wouldn’t know about until you needed the brakes on the road.

Emergency Mobile Diesel Service for Farms and Roadside / Central and Southern Arkansas .
870-941-6160

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2100 Highway 46 North
Sheridan, Arkansas 72150
e-mail – [email protected]  
Call Rusty – 870-941-6160

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