CDL Air Brakes Practice Test 2
What is the primary purpose of a front brake limiting valve?
Cuts the air pressure to the front brakes by half. If your vehicle is made before 1975, it may be equipped with a front brake limiting valve which can cut the air pressure to the front brakes by half. The valve will decrease the s
Which of the following will affect the stopping power of spring brakes?
All of the above. Road conditions (e.g., slippery, icy etc.) always effect stopping power. Spring brakes need to be properly adjusted in order to work right. A modulating control valve is a control handle (on some vehicles) that
A dual air brake system has which of the following features?
One set of brake controls and two separate air brake systems. Most heavy-duty vehicles use dual air brake systems that have a single set of brake controls, but two separate air brake systems.
Where are foundation brakes used?
On all wheels. Foundation brakes (usually s-cam drum brakes) are used at each wheel to provide equal stopping power. Commercial vehicles have emergency and parking brakes in addition to foundation brakes.
Which of the following parts of the air brake systems should be checked during the pre-trip walk around inspection?
All of the above. During step 5 of the pre-trip inspection, you should check the slack adjuster, air hoses and brake drums/discs of the air brake systems.
During inspection, if a slack adjuster moves less than about one inch where the push rod attaches to it, which of the following statements is true?
It has the appropriate amount of slack. If the slack adjuster moves MORE than about one inch, it probably needs adjustment and will not pass roadside inspections. Too much brake slack will make the vehicle very hard to stop.
When testing the air leakage rate (by turning off the engine and releasing the parking brake), what is an acceptable air loss rate?
Less than 2 psi in one minute for single vehicles and less than 3 psi in one minute for combination vehicles. You should test for air leakage with a fully-charged air system. The loss rate should be less than two psi in one minute
Which of the following is not a step in testing that the spring brakes come on automatically?
Pull out the parking brake control knob. To check that spring brakes come on automatically, you should: chock the wheels, release the parking brake, shut the engine off and pump the brakes repeatedly (to reduce air pressure). The
If you use controlled braking, which of the following is an acceptable procedure?
Release the brakes if you need to make a large steering adjustment. In controlled braking, you apply the brakes as hard as you can without locking the wheels. If you need to make steering adjustments, you should release the brakes
What should you do if the low air pressure warning light comes on?
Stop and safely park your vehicle as quickly as possible. If the low air pressure warning comes on there might be a leak in the system. This means that you are in danger of losing your braking ability and you should stop and safel
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