Montana CDL: Air Brakes Practice Test

Not quite. The answer is at all wheels.

Foundation brakes are found at each wheel. The most common type of foundation brake is the S-cam drum brake.

Not quite. The answer is brake in a straight line.

In controlled braking, you brake as hard as you can without locking the wheels. As you do this, keep your vehicle going relatively straight.

Not quite. The answer is Yes, but only if the alcohol evaporator is located downstream from the air dryer.

The air dryer contains a desiccant pack. A desiccant is a chemical agent designed to remove moisture. However, alcohol vapor from the alcohol evaporator (injector) can damage the desiccant. Hence, if an alcohol evaporator is installed, it must be located downstream from the air dryer.

Not quite. The answer is 1 inch

During the walk-around inspection, pull hard on each slack adjuster that you can reach. If it moves more than an inch, it probably needs adjustment.

Not quite. The answer is 60 psi.

A low pressure warning signal visible to the driver must come on before the pressure in the service air tank falls below 60 psi (or one-half the air compressor governor cutout air pressure on older vehicles).

Not quite. The answer is park on level ground, chock the wheels, and release the parking brakes.

The slack adjusters won't move if the parking brakes are on. To check the slack adjusters, park on level ground, chock the wheels, and then release the parking brakes. Use gloves and pull hard on each slack adjuster that you can reach. If a slack adjuster moves more than about one inch where the pushrod attaches to it, it probably needs adjustment.

Not quite. The answer is Every time you leave your vehicle, with a few exceptions

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is Leaky glad hand seals

Glad hands have rubber or urethane seals to form a tight connection and prevent air from escaping. The glad hands are constantly being connected and disconnected, so the seals tend to wear out over time. Leaky seals can cause loss of air pressure.

Not quite. The answer is service

Air brakes are really three braking systems in one: the emergency brake, the parking brake, and the service brake. As these names suggest, when you depress the brake pedal in normal driving, it's the service brake system that applies the brakes.

Not quite. The answer is stop braking, turn quickly, and countersteer.

To recover from a drive-wheel braking skid, first stop braking. The rear wheels will unlock and roll again so there will be no more tendency to slide sideways. Then quickly steer your vehicle back on course. You may find that your vehicle will overshoot and keep on turning, possibly skidding in the opposite direction. Countersteer to counteract this. Note: This maneuver takes some practice. You should become proficient in it before you actually need to use it.

Not quite. The answer is vehicles with air brakes.

A low air pressure warning signal is required on vehicles with air brakes. The warning is usually a red light. A buzzer may also come on. Another type of warning is the “wig wag.” This device drops a mechanical arm into your view when the pressure in the system drops between the dangerous levels.

Not quite. The answer is press the brake pedal as hard as you can, release the brakes when the wheels lock, and apply the brakes again when the wheels start to roll.

To stop with stab braking, brake hard, release the brakes once the wheels lock, and then brake hard once the wheels start to roll again. (Note that this method won't work if your vehicle has antilock brakes, because the wheels won't lock. Use controlled braking instead.)

Not quite. The answer is yellow

If your vehicle has ABS, there will be a yellow ABS malfunction lamp on the instrument panel. When you start the engine, the ABS malfunction lamp will come on momentarily to show that the lamp works. But if the lamp comes on and stays on, it means there is a problem with the ABS.

Not quite. The answer is forces the brake shoes against the inside of the brake drum.

When the S-cam rotates, it forces the brake shoes apart and against the inside of the brake drum. Friction will slow the rotation of the wheel.

Not quite. The answer is a supply pressure gauge.

Every vehicle with air brakes has a supply pressure gauge, which shows how much air pressure is in the air tanks. Some vehicles also have an application pressure gauge, which shows how much air pressure you are applying to the brakes. Older vehicles also had a manual front brake limiting valve, which allowed the driver to cut front brake air pressure in half as a way of preventing front-wheel skids. However, tests have shown that full front-wheel braking is safe.

Not quite. The answer is one-half

During your walk-around inspection, check the brake drums or brake discs to be sure that no cracks are longer than half the width of the friction area.

Not quite. The answer is brake drum.

In North America, the most common type of foundation brake is the S-cam drum brake. The brake shoes and linings press against the inside of the brake drum, which causes friction to slow the wheel.

Not quite. The answer is They work as a supplement to the braking effect of your engine.

When you drive down long, steep downgrades, the braking effect of your engine is what's most important, and your brakes are only a supplement to being in the proper low gear. They cannot compensate for your vehicle being in an unsafe high gear without putting too much pressure on your brakes.

Not quite. The answer is Never

Never leave your vehicle unattended without first applying the parking brakes or chocking the wheels. Your vehicle might roll away and hit something – or someone.

Not quite. The answer is With the engine off, step on and off the brake pedal to lower the air pressure below 60 psi.

The best way to test the low air pressure warning signal is to release the parking brake (all vehicles), release the tractor protection valve (on combination vehicles), and turn off the engine of your vehicle while leaving the electrical power on. Then step on and off the brake pedal. The low air pressure warning signal should come on when the pressure falls below 60 psi. You should never need to get down to 30 psi.