T4 ASE BRAKES (MEDIUM/HEAVY
DUTY BRAKES) EXAM QUESTIONS
AND ANSWERS
The air system is maintained at what pressure? - ANSWER - 100 to 120 pounds per square inch.
At what pressure does the low pressure switch activate? - ANSWER - Below 60 pounds per square inch.
A safety or pop off valve is usually installed in which reservoir? - ANSWER - In the one closest to the
compressor.
Why is the Wet tank referred to as such? - ANSWER - It is the one closest to the compressor and has the
most water in it.
What is an after cooler used for in an air system? - ANSWER - It condenses and eliminates most of the
water from an air system.
What does an air drier do in a air system? - ANSWER - They usually contain a bed of desiccant material
which captures water and oil.
What does the dual control foot valve control? - ANSWER - After the wet tank the valve controls the
primary and secondary systems.
In a normal operation what does the primary air brake system control? - ANSWER - The rear axle brakes.
In a normal operation what does the secondary air brake system control? - ANSWER - The front axle
brakes.
, What does the two way check valve do in the air brake system? - ANSWER - It allows dominant pressure
to activate the stoplight switch and to release the parking brakes.
What is the standard releases of the parking brake system in the event of a failure? - ANSWER - At least
once during a failure of either primary or secondary system pressure.
Why are relay valves used in a rear air brake system? - ANSWER - To minimize delay of brake application
on long wheel based applications.
What determines the crack pressures on a air brake system relay valve? - ANSWER - How heavily loaded
the axle is. The size of the axle's brakes. Aggressiveness of the linings.
What is a quick release valve used for in air brake systems? - ANSWER - It allows brake actuation air to
be quickly exhausted near the brakes it serves.
What is the minimum apply time of air brake systems? - ANSWER - 0.45 seconds.
What is the minimum release time of air brake systems? - ANSWER - 0.55 seconds.
What is a ratio valve in air brake systems? - ANSWER - Also known as a pressure reducing valve, limits air
pressure to the front axle. They have a variety of hold off pressures.
What is the first step in system diagnosis of air brake systems? - ANSWER - The driver should be
interviewed.
If air brake systems are not applying and releasing properly, and grabbing or dragging what could be the
cause? - ANSWER - Defective supply system components.
If air brake systems have instability and premature wear what could be the cause? - ANSWER - As little
as a 4 pounds per square inch difference between axles can cause this.
DUTY BRAKES) EXAM QUESTIONS
AND ANSWERS
The air system is maintained at what pressure? - ANSWER - 100 to 120 pounds per square inch.
At what pressure does the low pressure switch activate? - ANSWER - Below 60 pounds per square inch.
A safety or pop off valve is usually installed in which reservoir? - ANSWER - In the one closest to the
compressor.
Why is the Wet tank referred to as such? - ANSWER - It is the one closest to the compressor and has the
most water in it.
What is an after cooler used for in an air system? - ANSWER - It condenses and eliminates most of the
water from an air system.
What does an air drier do in a air system? - ANSWER - They usually contain a bed of desiccant material
which captures water and oil.
What does the dual control foot valve control? - ANSWER - After the wet tank the valve controls the
primary and secondary systems.
In a normal operation what does the primary air brake system control? - ANSWER - The rear axle brakes.
In a normal operation what does the secondary air brake system control? - ANSWER - The front axle
brakes.
, What does the two way check valve do in the air brake system? - ANSWER - It allows dominant pressure
to activate the stoplight switch and to release the parking brakes.
What is the standard releases of the parking brake system in the event of a failure? - ANSWER - At least
once during a failure of either primary or secondary system pressure.
Why are relay valves used in a rear air brake system? - ANSWER - To minimize delay of brake application
on long wheel based applications.
What determines the crack pressures on a air brake system relay valve? - ANSWER - How heavily loaded
the axle is. The size of the axle's brakes. Aggressiveness of the linings.
What is a quick release valve used for in air brake systems? - ANSWER - It allows brake actuation air to
be quickly exhausted near the brakes it serves.
What is the minimum apply time of air brake systems? - ANSWER - 0.45 seconds.
What is the minimum release time of air brake systems? - ANSWER - 0.55 seconds.
What is a ratio valve in air brake systems? - ANSWER - Also known as a pressure reducing valve, limits air
pressure to the front axle. They have a variety of hold off pressures.
What is the first step in system diagnosis of air brake systems? - ANSWER - The driver should be
interviewed.
If air brake systems are not applying and releasing properly, and grabbing or dragging what could be the
cause? - ANSWER - Defective supply system components.
If air brake systems have instability and premature wear what could be the cause? - ANSWER - As little
as a 4 pounds per square inch difference between axles can cause this.
