Question 1

Which of the following best describes the role of an air compressor?

Accepted Answer

An air compressor functions as an air pump, compressing air and increasing its pressure for various applications, such as powering pneumatic tools or inflating tires.

Question 2

Which of the following correctly describes the function of an automatic slack adjuster?

Accepted Answer

Automatic slack adjusters perform multiple functions in a braking system, including converting linear force to torque, acting as a lever to increase mechanical advantage, and automatically adjusting the brake's free stroke to compensate for wear in the friction linings.

Question 3

What is primarily used to cool air compressors on most truck air brake systems?

Accepted Answer

Engine coolant is primarily used to cool air compressors on most truck air brake systems, as it efficiently transfers heat away from the compressor, helping to maintain optimal operating temperatures.

Question 4

When a driver is using the trailer hand brake valve to stop a rig and then stomps on the treadle valve,what is the source of the trailer service control signal?

Accepted Answer

The trailer service control signal comes from the tractor primary circuit when a driver uses the trailer hand brake valve and then applies the treadle valve. This is because the primary circuit is responsible for controlling the braking system in a tractor-trailer setup, ensuring that the signal for braking is properly communicated from the tractor to the trailer.

Question 5

Aerodynamic tractor-trailer rigs should have what effect on vehicle braking?

Accepted Answer

The answer of Aerodynamic tractor-trailer rigs should have what effect...

Question 6

How many supply tanks would a typical tractor-trailer semi-combination rig be equipped with?

Accepted Answer

Typically, a tractor-trailer semi-combination rig is equipped with one supply tank for the entire rig, which is located on the tractor. The trailer does not have its own supply tank.

Question 7

What would occur if all of the air leaked out of one hold-off chamber while a vehicle was moving down the highway?

Accepted Answer

When air leaks out of a hold-off chamber, the spring brake (which is held back by air pressure under normal conditions) would automatically apply on the affected wheel to ensure safety. This is because the spring brake system is designed to engage in the absence of sufficient air pressure.

Question 8

When under severe braking,the wheels of a trailer lock causing it to spin around while the tractor remains in a straight-ahead position,the condition is known as:

Accepted Answer

Trailer swing occurs when the wheels of a trailer lock during severe braking, causing the trailer to swing out to one side while the tractor continues moving straight ahead. This is different from a jackknife, where both the tractor and trailer fold towards each other.

Question 9

Technician A says that most air brake system safety pop-off valves trip open at 150 psi.Technician B says that a safety pop-off valve should be fitted to the system supply tank.Who is correct?

Accepted Answer

Most air brake system safety pop-off valves are indeed designed to trip open at around 150 psi to prevent over-pressurization and potential damage or failure of the air brake system. Additionally, it is standard practice and a safety requirement to fit a safety pop-off valve to the system supply tank to ensure the system is protected from excessive pressure.

Question 10

When the governor routes air to the compressor unloader circuit,what happens?

Accepted Answer

When the governor routes air to the compressor unloader circuit, it causes the compressor intake valves to be held open. This prevents the compressor from compressing air, effectively unloading it, and is a method to control the system air pressure by stopping the compression process when the system reaches its maximum designed pressure.

Question 11

When S-cam brakes are properly adjusted,which of the following conditions will result in the most service brake torque?

Accepted Answer

Maximum service brake pressure results in the most service brake torque because it directly increases the force applied by the brake shoes against the drum, enhancing braking effectiveness.

Question 12

Which of the following terms is used to describe an air brake treadle valve on a CMVSS 121 compliant highway tractor?

Accepted Answer

The terms "foot valve," "service brake valve," and "dual circuit application valve" are all used to describe an air brake treadle valve on a CMVSS 121 compliant highway tractor, indicating that all of the provided options are correct.

Question 13

Which of the following is true of an automatic slack adjuster?

Accepted Answer

Automatic slack adjusters are designed to maintain the correct distance between the brake shoes and the drum as the friction materials wear down, ensuring the brakes are properly adjusted at all times.

Question 14

Which of the following components functions to control the compressor effective cycles?

Accepted Answer

The governor controls the compressor's effective cycles by regulating the air pressure in the system, signaling the compressor to start or stop to maintain the desired pressure range.

Question 15

Technician A says that brake chambers convert air pressure into rotary force.Technician B says that slack adjusters convert rotary force into linear force.Who is correct?

Accepted Answer

Brake chambers convert air pressure into linear force to apply the brakes, not rotary force. Slack adjusters help maintain the correct distance between the brake shoes and the drum, rather than converting rotary force into linear force.

Question 16

Technician A says that Rockwell automatic slack adjusters generally use stroke-sensing adjustment on the release stroke.Technician B says that Gunnite slack adjusters use clearance-sensing adjustment on the apply stroke.Who is correct?

Accepted Answer

Both Technician A and Technician B are correct. Rockwell automatic slack adjusters typically use a stroke-sensing mechanism during the release stroke to adjust, while Gunnite slack adjusters often use a clearance-sensing mechanism during the apply stroke for adjustment.

Question 17

Technician A says that automatic slack adjusters are required to be fitted to all currently manufactured highway tractors and trailers.Technician B says that it is recommended that an automatic slack adjuster is not adjusted after being put in service.Who is correct?

Accepted Answer

Automatic slack adjusters are indeed required on all newly manufactured highway tractors and trailers to ensure consistent brake adjustment. Technician B is correct because, typically, automatic slack adjusters are designed to maintain the correct brake adjustment automatically and should not need manual adjustment once in service, except under specific circumstances or for maintenance purposes.

Question 18

What is the function of the compressor on a truck air brake system?

Accepted Answer

The primary function of the compressor in a truck air brake system is to compress ambient air to create the necessary pressure for the braking system to function effectively.

Question 19

If a spring brake assembly has 90 psi acting on the hold-off diaphragm and no air pressure acting on the service diaphragm,how much linear force is delivered to the slack adjuster?

Accepted Answer

The answer of If a spring brake assembly has 90...

Question 20

When 1000 pounds of linear force is delivered to a 6-inch slack adjuster,how much brake torque is produced at the S-camshaft?

Accepted Answer

The brake torque produced at the S-camshaft can be calculated using the formula: Torque = Force x Distance. In this case, the force is 1000 pounds and the distance (lever arm length) is 6 inches, which needs to be converted to feet for consistency in units (6 inches = 0.5 feet). Therefore, the torque is 1000 pounds * 0.5 feet = 500 lb-ft.

Quiz 28: Truck Brake Systems