Question 1

When using a spring disarmament chamber to disarm a spring brake,specifically what must be cut with an oxy-acetylene torch before you open the chamber after the procedure?

Accepted Answer

The spring chamber band clamp must be cut to safely release the tension of the spring inside the chamber before opening it.

Question 2

Technician A says that to increase governor cut-out pressure,the jam nut should be released and the adjusting screw turned CW.Technician B says that turning a governor adjusting screw CW increases the governor spring pressure.Who is correct?

Accepted Answer

The answer of Technician A says that to increase governor...

Question 3

Assuming a major air leak in tractor-trailer combination that will result in complete system air pressure loss,which of the following sequence of events will occur FIRST?

Accepted Answer

The spring brakes in a tractor-trailer combination are designed to automatically apply when the air pressure in the system drops below a certain threshold, typically around 60 psi (4 bar). This safety feature ensures that the vehicle can be brought to a stop in the event of a major air leak.

Question 4

When the differential between governor cut-out and cut-in pressures is less than 20 psi,which of the following will more probably result?

Accepted Answer

When the differential between governor cut-out and cut-in pressures is less than 20 psi, it results in increased compressor cycling frequency because the compressor has to turn on and off more frequently to maintain the pressure within the narrow range.

Question 5

When you are using visual stroke indicators to assess slack adjuster stroke,which of the following is required?

Accepted Answer

All of the options listed are required when using visual stroke indicators to assess slack adjuster stroke. The system air must be at system pressure to ensure accurate measurement, the parking brake should be released with wheels chocked for safety, and observation should occur as service brakes are applied to accurately assess the stroke.

Question 6

What is the typical service life of an air dryer desiccant cartridge?

Accepted Answer

The answer of What is the typical service life of...

Question 7

A truck driver complains that air is being discharged from somewhere in the supply circuit at a frequency of every minute or so: there is no evidence of continuous air leakage on the truck.Which of the following should be checked out first?

Accepted Answer

The correct answer is D) defective air dryer purge valve. This is because the air dryer purge valve is responsible for releasing air and moisture from the air brake system, and if it is defective, it could cause air to be discharged intermittently, matching the truck driver's complaint. Continuous air leakage would suggest a different issue, but the intermittent discharge points towards a problem with the air dryer purge valve.

Question 8

Who is responsible for defining OOS criteria on highway trucks?

Accepted Answer

The Commercial Vehicle Safety Alliance (CVSA) is responsible for defining Out-of-Service (OOS) criteria for highway trucks. These criteria are used during inspections to determine whether a vehicle is safe to continue operating on public roadways.

Question 9

Technician A says that most truck compressors today are seldom rebuilt in the field today.Technician B says that it most cases it is cost effective to rebuild compressors in the shop rather than stock rebuilt/exchange units.Who is correct?

Accepted Answer

Most truck compressors today are seldom rebuilt in the field due to the complexity of the task and the availability of exchange units, making Technician A correct. It is generally not cost-effective to rebuild compressors in the shop for most operations, contrary to Technician B's statement.

Question 10

You are replacing a spring brake chamber on a truck drive axle with a one with a pushrod that must be cut to size.Which of the following MUST be performed to properly fit the new spring brake chamber?

Accepted Answer

Cutting the pushrod to the correct size is essential to ensure that the slack adjuster angle is 90 degrees when the brakes are fully applied. This angle is critical for optimal brake performance and safety.

Question 11

If a truck brake system is functioning properly,when should the low air pressure warnings (buzzer and light)be illuminated

Accepted Answer

The low air pressure warnings in a truck's brake system are designed to activate when the air pressure drops to a specific threshold, typically between 70-60 psi (4.8 - 4.1 bar), to alert the driver of potential brake system issues before the pressure drops to a dangerously low level.

Question 12

Technician A says that if the electrical supply to an air dryer is interrupted,the dryer purge valve will immediately cease to function.Technician B says that the heater used in many air dryers is cycled by a thermostat.Who is correct?

Accepted Answer

Technician B is correct because the heater in many air dryers is indeed controlled by a thermostat to regulate the temperature and prevent overheating or underheating, ensuring the air dryer operates efficiently. Technician A is incorrect because if the electrical supply to an air dryer is interrupted, the purge valve may not immediately cease to function; it depends on the design of the air dryer system and the type of purge valve used.

Question 13

Which of the following tests is commonly used by roadside enforcement officers to quickly verify that a truck air supply system is performing to CVSA standards?

Accepted Answer

The air build-up test from 85-100 psi (5.8-6.9 bar) is a common method used by roadside enforcement officers to quickly verify that a truck's air supply system is performing to Commercial Vehicle Safety Alliance (CVSA) standards. This test checks the efficiency of the air compressor in replenishing the air system within a specific pressure range, which is critical for the safe operation of the vehicle's air brakes.

Question 14

What brake diagnostic tool is used to measure the change in angle of a truck chassis when it is subjected to aggressive braking?

Accepted Answer

The answer of What brake diagnostic tool is used to...

Question 15

Technician A says that most modern friction facings used on truck drum brake shoes are much softer than the asbestos facings used a generation ago.Technician B says that a disadvantage of modern friction facings is that they destroy brake drums at a much faster rate than asbestos facings.Who is correct?

Accepted Answer

The answer of Technician A says that most modern friction...

Question 16

Technician A says that a truck with an FMVSS-121 air system must have a minimum of three air reservoirs.Technician B says that some FMVSS-121 compliant trucks use a single tank,divided internally into three reservoirs.Who is correct?

Accepted Answer

FMVSS-121 requires a specific air reservoir capacity for air brake systems, but it doesn't specify the number of tanks. Some systems use multiple tanks, while others use a single tank with internal divisions to meet the requirements, making both Technician A and B correct in their statements.

Question 17

Where does the governor sense air pressure?

Accepted Answer

The answer of Where does the governor sense air pressure?
...

Question 18

When you are installing open anchor brake shoes (such as Q-brakes)which of the following steps should be performed first?

Accepted Answer

The answer of When you are installing open anchor brake...

Question 19

Technician A says that when you observe excessive slack adjuster pushrod travel,the slack adjuster is probably over-adjusting.Technician B says that an over-adjusting slack adjuster must be replaced.Who is correct?

Accepted Answer

Excessive slack adjuster pushrod travel typically indicates under-adjustment or a malfunction, not over-adjustment. An over-adjusting slack adjuster doesn't necessarily need to be replaced; it may require adjustment or servicing.

Question 20

If there is air leakage in the governor unloader circuit,which of the following will more likely result?

Accepted Answer

Air leakage in the governor unloader circuit can lead to the compressor cycling on and off more frequently than normal because the system struggles to maintain the required pressure, causing the compressor to activate more often to compensate for the lost pressure.

Quiz 31: Air Brake Servicing