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Practice for your Air Brakes CDL exam with questions based on the official Iowa CDL handbook
If your vehicle doesn't have automatic tank drains, you should drain the oil and water from the bottom of the air tanks ___.
Drain the oil and water from your truck's air tanks at the end of each day of driving if they don't have auto drains. This keeps the brakes working right.
What does the air compressor governor control?
The air compressor governor decides when to fill up the air tanks used for brakes and other parts. It doesn't control the engine's fuel use or temperature.
If you pull hard on a slack adjuster and it moves more than ___, it needs to be adjusted.
If the slack adjuster moves more than 1 inch when you pull on it, it's too loose and needs adjusting. This is important for the brakes to work right.
If the air pressure doesn't go up to the needed level fast enough, then:
If the air pressure in your truck doesn't build up fast enough, it can get too low while you're driving. This means you might have to suddenly stop your truck to avoid problems.
Parking or emergency brakes must be kept in position by something that does not leak, like:
The right answer is spring pressure. This is because parking or emergency brakes in vehicles need a reliable way to stay active. Springs can do this without the risk of losing power, unlike systems that depend on magnets or electricity, which can fail if there's a power loss or leak.
Excessive heat caused by overusing your brakes can also cause ___.
Using your brakes too much can make them too hot. When they get too hot, they might not work right or could stop working altogether.
At what psi does the air compressor stop pumping air?
The air compressor stops pumping air at 125 psi because this is the standard pressure level needed to maintain the air brake system's functionality without overloading it. This ensures that the system has sufficient air pressure to operate safely while preventing potential damage or inefficiencies from excessive pressure.
What brake system applies and releases the brakes when the driver steps on the brake pedal?
The correct answer is "Service." This is the brake system in a vehicle that works when the driver pushes the brake pedal to slow down or stop the truck. It's the main system used for everyday driving.
The safety valve lowers pressure when it reaches ___ psi.
The safety valve helps keep the air pressure in the brakes from getting too high. It does this by letting some air out when the pressure hits 150 psi. This makes sure the brakes work right and stay safe.
What happens if your vehicle's brake drums overheat?
When your brake drums get very hot, they expand. This means they get bigger because of the heat.
Why is it important to remove water from the compressed air tanks?
Draining water from air tanks is important because in cold weather, it can freeze and stop your brakes from working right.
When going down a steep hill and reaching your safe speed of 40 mph, you would use the brake until your speed goes down to _____ mph.
When driving down a steep hill and you're at your safe speed of 40 mph, hit the brakes until you slow down to 35 mph. Then, let go of the brakes to avoid overusing them.
When you use the service brakes too much, they can get too hot and this can cause ___.
When you use the brakes too much, they can get really hot. This heat can make the brake drums (part of the brakes) get bigger. This doesn't help the car save gas or change the air in the tires; it just makes the brakes work less effectively.
Your truck is equipped with a dual air brake system and minimum-size air tanks. How long should it take for the air pressure to go up from 85 to 100 psi?
When your truck's air brake system is in good shape and the tanks are the smallest allowed, the air pressure should go from 85 to 100 psi in 45 seconds or less. This shows your brakes are working right and can safely stop the truck.
What does the term "Wig Wag" mean?
The term "Wig Wag" refers to a safety device in air brake systems that uses a mechanical arm to alert the driver when air pressure drops to a dangerously low level. This visual warning helps ensure the driver takes immediate action to prevent brake failure, maintaining safety on the road.
What statement about spring brake braking power is correct?
The spring brakes on a vehicle work properly only if the regular brakes (service brakes) are set up right. If the service brakes are not adjusted correctly, the spring brakes won't be able to do their job well. So, the power of the spring brakes relies on the service brakes being properly adjusted.
How do you normally engage the parking brakes?
Engaging the parking brake is all about ensuring your car stays put once parked. By pulling out the control knob, you directly activate the brake system that keeps the vehicle stationary.
When the air pressure falls below ___ psi, the straight truck spring brakes will come fully on.
When driving a straight truck, if the air pressure gets too low, special brakes called spring brakes kick in to stop you. This happens when the air pressure drops below 20 psi (pounds per square inch). It's a safety feature to prevent accidents when there's not enough air pressure for the regular brakes.
What is the purpose of a brake light switch?
A stop light switch makes the brake lights turn on when you use the air brakes. This lets other drivers know you're slowing down or stopping.
Which of the following types of foundation brakes are most commonly found on heavy vehicles?
The S-cam drum brake is the most common brake on big vehicles. It uses a special cam to push brake pads against a drum to stop the vehicle. This system is reliable and widely used in trucks and buses.
The Air Brakes test is required for anyone operating a vehicle equipped with air brakes in Iowa. It covers how air brake systems work, dual air brake systems, inspecting air brakes, and using them safely in all conditions.
The Air Brakes test is part of the CDL written exam administered by the Iowa Department of Motor Vehicles. You must pass this test along with the other required written tests to receive your Commercial Learner's Permit (CLP) in Iowa.
Our practice questions are built from the official Iowa CDL handbook and federal FMCSA regulations. Each question includes a detailed explanation to help you understand the material, not just memorize answers.
