Oklahoma CDL: Air Brakes Practice Test

Not quite. The answer is release the spring brakes.

When main air pressure is lost, the spring brakes come on and stop your vehicle. Some vehicles such as buses have a separate air tank with enough air to release the spring brakes in case the vehicle must be moved temporarily in an emergency. (The tank holds only enough air to do this a few times, however.) You control this action with the dual parking control valve.

Not quite. The answer is If the brakes are very hot

If the brakes are too hot, avoid using the parking brakes because the heat may warp and damage the brakes. Also avoid using the parking brakes if they are wet and at risk of freezing. If the parking brakes freeze, your vehicle will be immobilized. In both of these situations, use wheel chocks instead.

Not quite. The answer is They help maintain correct pushrod stroke.

An automatic slack adjuster automatically compensates for normal brake lining wear by adjusting pushrod stroke. Automatic slack adjusters should not normally require manual adjustment of pushrod stroke. However, they still require lubrication at regular intervals.

Not quite. The answer is reduce air pressure at the front wheels.

Most modern tractors are equipped with an automatic front axle ratio valve, which supersedes the manual front brake limiting valve in older tractors. In light-to-moderate braking, the ratio valve automatically reduces air pressure (and hence braking force) to the front wheels to reduce the chance of front-wheel lockup (which could result in a skid) on slippery roads.

Not quite. The answer is The brakes could fail.

Water and oil from the compressor can collect at the bottoms of the air tanks. If the air tanks are not drained regularly, the water and oil can freeze or coagulate and cause brake failure.

Not quite. The answer is At the end of each working day

Unless your vehicle automatically drains the air tanks, you should drain them at the end of each working day so that the moisture and oil will not freeze or coagulate and cause your brakes to fail.

Not quite. The answer is 100 psi.

In a typical air brake system, pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check the manufacturer's specifications for the actual figures.)

Not quite. The answer is Stop and park safely.

If the low air pressure warning comes on, there may be a leak in the system. Pull over and park your vehicle as soon as possible. If the air pressure drops too low, the spring brakes will come on automatically, which will stop your vehicle – but not necessarily in a safe way. Sudden application of the spring brakes while you're driving might result in a skid.

Not quite. The answer is Park on level ground, turn off the parking brakes, and pull hard on each slack adjuster.

To check the slack adjusters, try to pull on them manually while wearing gloves. If there is an inch or more of "give," then there is an issue and they should be fixed.

Not quite. The answer is Between the compressor and the first air tank

An air dryer may be installed in the compressor discharge line between the compressor and the first air tank. Its purpose is to remove water vapor and contaminants from compressor air before the air enters the first tank. The first tank has usually been the supply or "wet" tank, so called because moisture accumulated in that tank before the air flowed from there to the service tanks. However, today's air dryer technology is so effective that a "wet" tank may not be needed anymore. In a modern Air Dryer Integrated System (AD-IS®), the air compressor governor and the air dryer are combined into a single unit. Air from the air dryer goes directly into the primary and secondary service ("dry") tanks. There is no supply ("wet") tank.

Not quite. The answer is All weather conditions

Front wheel brakes have been shown to be ideal under all weather and driving conditions. Front wheel braking is unlikely to cause a skid even on icy roads.

Not quite. The answer is 150 psi

The safety valve, which protects the system from excessive pressure, is usually set to open when the system reaches 150 psi.

Not quite. The answer is All of the above are correct.

On both tractor-trailers and single vehicles, to test whether the spring brakes will come on automatically, use the same method you use for testing the low air pressure warning signal: Step on and off the brake pedal, this time until you reach an even lower psi reading and the parking brake valve closes or pops out.

Not quite. The answer is depends on whether the service brakes are in proper adjustment.

The braking power of the spring brakes depends on whether the service brakes are in proper adjustment. If they are not, neither the service brakes nor the emergency/parking brakes will work properly.

Not quite. The answer is To avoid injury from high-pressure air and debris

Compressed air may be exhausted from several different ports in the air braking system. This air travels at a very high speed from the vehicle and carries moisture, oil, dirt, and dust. It can be dangerous if it hits your eyes or ears. Know the location of all air exhaust ports so you can keep away from them, such as when you're draining the air tanks.

Not quite. The answer is Evacuate the air from the brake chambers.

In today's CMVs, you apply or release the parking brakes with the parking brake control on the dashboard. This is a diamond-shaped, yellow, push-pull control knob. To apply the parking brakes, pull out the knob to evacuate the air from each brake chamber, which will cause the spring brakes to come on.

Not quite. The answer is release the spring brakes.

Even after loss of air pressure has caused the spring brakes to come on, you may need to move the vehicle again in an emergency. Some vehicles such as buses have a separate air tank that can be used to release the spring brakes. You can then move the vehicle, after which you can set the spring brakes again. This action is controlled by dual parking control valves: One valve lets air flow from this air tank to release the spring brakes, and the other valve sets them again.

Not quite. The answer is to tell you how much air is in the tank.

The supply pressure gauge tells you how much air is in the tank at all times. In some vehicles, it may be connected to a warning bell or light.

Not quite. The answer is Bring the vehicle to a safe stop and continue only after the system is fixed.

A dual air brake system has two separate air brake systems. Typically, the primary system operates the brakes on the rear axle(s), and the secondary system operates the brakes on the front axle (and possibly one rear axle). If one of these two systems loses air pressure (causing the low air pressure warning), either the front or the rear brakes won't work properly. As a result, your vehicle's braking distance will increase. If this happens, stop your vehicle and get the system fixed.

Not quite. The answer is by increasing and decreasing the air pressure.

The air compressor governor should cut in when a lower air pressure is reached and cut out when a higher air pressure is reached. (Check your manufacturer's specifications for these pressures.) To test this, run the engine at a fast idle to raise the air pressure until the air compressor governor cuts out. Then keep stepping on and off the brake pedal to reduce the air pressure until the air compressor governor cuts in.