T4 Medium/Heavy-Duty
Brakes test questions and
answers
What are symptoms of defective supply system components?
Brakes not applying/releasing properly and grabbing or dragging
How much of a difference in psi air delivery between axles can cause
instability and premature wear?
4-psi
If all-around braking performance is poor or if the system is not building
up enough air pressure, look for signs such as:
A clogged air compressor filter, slipping belt, air leaks, restricted lines, a
defective governor, or even a malfunctioning air compressor
What is an air brake governor?
An air brake governor controls the compressor. It maintains reservoir air
pressure between a predetermined min. and max. air pressure.
If system pressure is too high suspect a:
Defective governor or reservoir safety valve.
If a governor's cut-out pressure is too high, it can cause:
Over-pressurization
A faulty reservoir safety valve:
May not be allowing excessive air pressure to be purged from the air tanks
When releasing the service brakes and timing the air pressure drop, the
loss rate should be less than ___psi/minute for straight trucks and less
than ___psi/minute for combination vehicles.
Less than 2psi/minute for straight trucks and less than 3psi/minute for
combination vehicles.
When applying the service brakes to at least 90 psi and timing the air
pressure drop, the loss rate should be less than ___psi/minute for straight
trucks and less than ___psi/minute for combination vehicles.
Less than 3psi/minute for straight trucks and less than 4psi/minute for
combination vehicles.
, Trucks with air brakes come equipped with pressure gauges mounted on
the dash. The gauges will indicate:
How much air pressure is in the system at any given time
When system pressures fall below ___ psi, either a warning light will
illuminate, or a buzzer will sound.
60 psi
Some systems include a _____ _______ gauge, which can inform the driver of
specific pressure when the brakes are applied.
Separate application gauge
Dash air pressure gauges operate on the principle of changing an:
Air brake pressure signal into an electronic voltage signal
An element inside an ___ ________ __________ responds to air pressure
increase or decrease, the __________ converts that pressure differentiation
into a voltage signal, which is displayed in a proportionate reading in the
dash gauge.
Air pressure transducer; transducer
To check the transducer and gauge assembly, make sure the air supply
value and transducer output voltage are within _______
The manufacturer's specifications
If the transducer voltage output is not within normal readings, suspect a
Defective transducer
If the transducer voltage output is within normal readings, suspect a
Defective gauge
A defective ________ device will fail to signal the driver of diminished air
pressure in the brake system.
Low-pressure warning device
The low-pressure warning indicator is installed on the ______ reservoir, and
notifies the operator of ____________.
Primary reservoir; system air depletion
To check the operation of the low-pressure warning indicator, completely
______ the air brake system.
Depressurize
If at 60 psi the low-pressure indicator signals do not operate, check for
______ at the warning device. If the circuit is open, suspect a ________.
Brakes test questions and
answers
What are symptoms of defective supply system components?
Brakes not applying/releasing properly and grabbing or dragging
How much of a difference in psi air delivery between axles can cause
instability and premature wear?
4-psi
If all-around braking performance is poor or if the system is not building
up enough air pressure, look for signs such as:
A clogged air compressor filter, slipping belt, air leaks, restricted lines, a
defective governor, or even a malfunctioning air compressor
What is an air brake governor?
An air brake governor controls the compressor. It maintains reservoir air
pressure between a predetermined min. and max. air pressure.
If system pressure is too high suspect a:
Defective governor or reservoir safety valve.
If a governor's cut-out pressure is too high, it can cause:
Over-pressurization
A faulty reservoir safety valve:
May not be allowing excessive air pressure to be purged from the air tanks
When releasing the service brakes and timing the air pressure drop, the
loss rate should be less than ___psi/minute for straight trucks and less
than ___psi/minute for combination vehicles.
Less than 2psi/minute for straight trucks and less than 3psi/minute for
combination vehicles.
When applying the service brakes to at least 90 psi and timing the air
pressure drop, the loss rate should be less than ___psi/minute for straight
trucks and less than ___psi/minute for combination vehicles.
Less than 3psi/minute for straight trucks and less than 4psi/minute for
combination vehicles.
, Trucks with air brakes come equipped with pressure gauges mounted on
the dash. The gauges will indicate:
How much air pressure is in the system at any given time
When system pressures fall below ___ psi, either a warning light will
illuminate, or a buzzer will sound.
60 psi
Some systems include a _____ _______ gauge, which can inform the driver of
specific pressure when the brakes are applied.
Separate application gauge
Dash air pressure gauges operate on the principle of changing an:
Air brake pressure signal into an electronic voltage signal
An element inside an ___ ________ __________ responds to air pressure
increase or decrease, the __________ converts that pressure differentiation
into a voltage signal, which is displayed in a proportionate reading in the
dash gauge.
Air pressure transducer; transducer
To check the transducer and gauge assembly, make sure the air supply
value and transducer output voltage are within _______
The manufacturer's specifications
If the transducer voltage output is not within normal readings, suspect a
Defective transducer
If the transducer voltage output is within normal readings, suspect a
Defective gauge
A defective ________ device will fail to signal the driver of diminished air
pressure in the brake system.
Low-pressure warning device
The low-pressure warning indicator is installed on the ______ reservoir, and
notifies the operator of ____________.
Primary reservoir; system air depletion
To check the operation of the low-pressure warning indicator, completely
______ the air brake system.
Depressurize
If at 60 psi the low-pressure indicator signals do not operate, check for
______ at the warning device. If the circuit is open, suspect a ________.
