ASE S4 Brakes Exam: 100% Verified Questions & 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.
If all around braking performance is poor or low air pressure is prevalent what could be the cause? -
ANSWER:Clogged compressor air filter. Slipping belt. Air leaks. Restricted lines. Defective governor.
Malfunctioning air compressor.
If air system pressure is too high what could be the cause? - ANSWER:Defective governor. Reservoir
safety valve. Governor's cut off pressure.
With the engine running at an idle what should be the pressure build up time? - ANSWER:85 to 100
pounds per square inch within 45 seconds. 25 seconds at full governed speed.
If air system pressure build up time takes too long what could be the cause? - ANSWER:Leaks. Dirty air
filter.
When draining the air tank you find excessive oil what could be the cause? - ANSWER:Blocked air filter. If
air filter not blocked then suspect worn compressor rings. Air drier ejection valve.
How often should self lubricated air compressor oil level checked? - ANSWER:Daily.
Before diagnosing the air system shut off the engine and then do what? - ANSWER:Block the wheels to
prevent vehicle movement.
How do you check the unloader valve on air compressors? - ANSWER:With air pressure applied squirt oil
around the unloader plunger and stem.
What is the cause of sludge build up inside the discharge line of air compressors? - ANSWER:Excessive oil
is passing the oil control rings.
What is the most common cause of premature ring damage? - ANSWER:Failure to change compressor
oil.
How can compressor air leakage be detected? - ANSWER:Engine off, listening at the compressor for the
sound of escaping air.
When checking air compressor cylinder heads and having applied 100 pounds per square inch through
the discharge port what is acceptable leakage at the valve? - ANSWER:It should not exceed a 1 inch soap
bubble every five seconds.
When checking the governor for leakage what is the allowable leakage at the exhaust valve? - ANSWER:It
should not exceed a 3 inch soap bubble every three seconds.
When checking the pressure protection valve what is the allowable leakage at the cap of the valve? -
ANSWER:It should not exceed a 1 inch soap bubble every five seconds.
When checking the pressure protection valve what is the allowable leakage at the bottom of the valve? -
ANSWER:There should be no leakage.
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.
If all around braking performance is poor or low air pressure is prevalent what could be the cause? -
ANSWER:Clogged compressor air filter. Slipping belt. Air leaks. Restricted lines. Defective governor.
Malfunctioning air compressor.
If air system pressure is too high what could be the cause? - ANSWER:Defective governor. Reservoir
safety valve. Governor's cut off pressure.
With the engine running at an idle what should be the pressure build up time? - ANSWER:85 to 100
pounds per square inch within 45 seconds. 25 seconds at full governed speed.
If air system pressure build up time takes too long what could be the cause? - ANSWER:Leaks. Dirty air
filter.
When draining the air tank you find excessive oil what could be the cause? - ANSWER:Blocked air filter. If
air filter not blocked then suspect worn compressor rings. Air drier ejection valve.
How often should self lubricated air compressor oil level checked? - ANSWER:Daily.
Before diagnosing the air system shut off the engine and then do what? - ANSWER:Block the wheels to
prevent vehicle movement.
How do you check the unloader valve on air compressors? - ANSWER:With air pressure applied squirt oil
around the unloader plunger and stem.
What is the cause of sludge build up inside the discharge line of air compressors? - ANSWER:Excessive oil
is passing the oil control rings.
What is the most common cause of premature ring damage? - ANSWER:Failure to change compressor
oil.
How can compressor air leakage be detected? - ANSWER:Engine off, listening at the compressor for the
sound of escaping air.
When checking air compressor cylinder heads and having applied 100 pounds per square inch through
the discharge port what is acceptable leakage at the valve? - ANSWER:It should not exceed a 1 inch soap
bubble every five seconds.
When checking the governor for leakage what is the allowable leakage at the exhaust valve? - ANSWER:It
should not exceed a 3 inch soap bubble every three seconds.
When checking the pressure protection valve what is the allowable leakage at the cap of the valve? -
ANSWER:It should not exceed a 1 inch soap bubble every five seconds.
When checking the pressure protection valve what is the allowable leakage at the bottom of the valve? -
ANSWER:There should be no leakage.
