Air System
What is the primary purpose of the air brake system on a tractor-trailer?
The air system supplies compressed air to operate the brakes. It allows the driver to safely slow down and stop the vehicle, and it also powers components like the parking brakes and sometimes the suspension.
What is the minimum legal tread depth for steer tires versus drive and trailer tires?
What is the purpose of the coupling system on a tractor-trailer?
The coupling system connects the tractor to the trailer. It secures the trailer for towing and allows transfer of weight, as well as providing connections for the air lines and electrical system.
What are the main engine fluids a driver should check during a pre-trip inspection?
Why are 4-inch straps used to secure steel on a flatbed, and what is their main function?
4" straps are used to apply downward force and keep the load from shifting. They are strong, flexible, and help protect finished steel surfaces from damage that chains might cause.
What is the normal operating air pressure range for a tractor-trailer?
Typically between 100–125 PSI. The governor usually cuts out around 120–140 PSI and cuts in around 100 PSI.
Why is proper tire inflation important, and how can a driver identify an underinflated tire during a pre-trip?
Proper inflation ensures safe handling, even wear, and prevents blowouts.
Signs of underinflation include:
What are the main components of the tractor-trailer coupling system?
What are you looking for when inspecting belts and hoses in the engine compartment?
What should you look for when inspecting 4-inch straps before use?
Any damaged strap should be taken out of service.
When should the low air pressure warning activate, and why is it important?
The low air warning (light and buzzer) should activate at approximately 60 PSI. It’s important because it alerts the driver that air pressure is dropping to an unsafe level, giving them time to stop before the brakes fail or spring brakes automatically apply.
What types of tire damage would make a tire unsafe to operate?
What should you look for when visually inspecting the fifth wheel and kingpin?
What are common signs of engine fluid leaks, and why are they dangerous?
Leaks are dangerous because they can lead to engine damage, overheating, loss of steering assist, or even fire hazards.
How do you determine if your 4-inch straps provide enough securement for a steel load?
Each 4" strap typically has a WLL around 5,400 lbs (check the tag).
The total combined WLL of all straps must equal at least 50% of the weight of the cargo.
If the load is heavier, more straps must be added to meet or exceed this requirement.
How do you properly perform an air leak test, and what are acceptable limits?
Acceptable loss:
What should you check between dual tires, and why is it important?
If one tire is underinflated, the other can become overloaded, leading to overheating or failure.
How do you perform a proper tug test, and what does it confirm?
This confirms the fifth wheel jaws are locked around the kingpin and the trailer is securely coupled.
What should you check on the alternator and related components during a pre-trip inspection?
A failing alternator can lead to loss of electrical power and eventually shut the vehicle down.
How should 4-inch straps be positioned on a steel load to prevent movement?
Improper placement can allow the load to shift even if the straps are tight.
How do spring brakes work, and what happens if the air system pressure is lost while driving?
Spring brakes are held released by air pressure and apply when air pressure is removed.
What are the signs of loose or damaged lug nuts or wheel issues during inspection?
These signs indicate the wheel may be loose or compromised, which can lead to wheel separation if not corrected.
What are signs of an improper or unsafe coupling, and what could happen if it’s not corrected?
Signs:
Consequences:
How does the engine cooling system work, and what specific components should be inspected to ensure it’s functioning properly?
The cooling system circulates coolant through the engine to absorb heat and release it through the radiator.
Key components to inspect:
If the cooling system fails, the engine can overheat quickly, leading to severe engine damage.
What are the requirements for checking strap securement during transit, and what issues are you looking for?
If straps loosen or shift, they must be re-tightened or adjusted immediately to prevent load movement.