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ASE S4 Brakes (School Bus) Practice Questions - ASE S4 - Brakes (School Bus) Certification Exam
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Question
1
of 25
QUESTION 1 / 25
A school bus air system builds pressure slowly. The compressor is engaging normally and the governor cuts out at the correct pressure. Which condition is the MOST likely cause of slow build-up?
Choose one answer below.
A
A restricted or contaminated air dryer or excessive system leakage
✓
B
A governor cut-out setting that is set too low
✓
C
An unloader that is stuck in the loaded position
✓
D
A relay valve with a defective exhaust port
✓
QUESTION 2 / 25
The air compressor governor on a school bus is responsible for which function?
Choose one answer below.
A
Metering air to the front service brakes during a stop
✓
B
Controlling compressor loaded/unloaded operation by cycling the unloader at cut-in and cut-out pressures
✓
C
Protecting the secondary reservoir if the primary circuit fails
✓
D
Limiting brake chamber pushrod travel as linings wear
✓
QUESTION 3 / 25
Technician A says the air dryer removes moisture and some oil from compressed air before it reaches the reservoirs. Technician B says a saturated desiccant cartridge can allow water to collect in the reservoirs. Who is correct?
Choose one answer below.
A
A only
✓
B
B only
✓
C
Both A and B
✓
D
Neither A nor B
✓
QUESTION 4 / 25
During an air dryer service, the technician finds the purge valve is not exhausting at governor cut-out. What is the MOST likely result?
Choose one answer below.
A
The compressor will fail to unload and overpressurize the system
✓
B
The trailer supply line will lose pressure during braking
✓
C
The spring brakes will apply with the parking control released
✓
D
Moisture and oil are not expelled, so contamination builds in the dryer and reservoirs
✓
QUESTION 5 / 25
What is the primary purpose of the one-way check valves located between the wet reservoir and the primary and secondary reservoirs?
Choose one answer below.
A
To prevent loss of stored air from one reservoir if another reservoir or the supply line fails
✓
B
To regulate the governor cut-in and cut-out pressures
✓
C
To exhaust moisture automatically from the wet tank
✓
D
To balance pressure between the front and rear brake circuits during a stop
✓
QUESTION 6 / 25
A school bus reservoir drained at the end of a shift shows a steady stream of oil and water. The air dryer was replaced recently. What should the technician inspect FIRST?
Choose one answer below.
A
The treadle valve for an internal leak
✓
B
The air compressor for excessive oil passing (worn rings or overhead) before condemning the new dryer
✓
C
The quick-release valve diaphragm
✓
D
The slack adjuster free travel
✓
QUESTION 7 / 25
On a dual air brake system, what does a low air pressure warning device do, and at approximately what pressure must it activate per FMVSS 121?
Choose one answer below.
A
It releases the spring brakes and activates at 45 psi
✓
B
It loads the compressor and activates at 85 psi
✓
C
It warns the driver and must activate at or below 60 psi
✓
D
It applies the service brakes and activates at 100 psi
✓
QUESTION 8 / 25
The compressor on a school bus runs continuously and never cuts out, but pressure stabilizes at about 95 psi. Governor cut-out is specified at 120 psi. Which is the MOST likely cause?
Choose one answer below.
A
Excessive air leakage or demand exceeding compressor output
✓
B
A governor set above specification
✓
C
A check valve installed backward in the supply line
✓
D
An air dryer purge valve stuck open continuously
✓
QUESTION 9 / 25
What is the function of the safety (pop-off) valve on the supply (wet) reservoir of a school bus air system?
Choose one answer below.
A
To relieve excessive reservoir pressure if the governor or compressor unloader fails
✓
B
To warn the driver of low air pressure
✓
C
To exhaust air rapidly from the brake chambers on release
✓
D
To proportion air between the front and rear axles
✓
QUESTION 10 / 25
A technician must test air system leakage on a school bus with the engine off and system fully charged. With the service brakes released, the maximum allowable pressure drop in one minute for a single vehicle (no trailer) is approximately:
Choose one answer below.
A
6 psi
✓
B
2 psi
✓
C
10 psi
✓
D
20 psi
✓
QUESTION 11 / 25
With the service brakes fully applied and the engine off on a charged single school bus, the maximum allowable air pressure loss in one minute is approximately:
Choose one answer below.
A
8 psi
✓
B
12 psi
✓
C
3 psi
✓
D
25 psi
✓
QUESTION 12 / 25
Technician A says the wet (supply) reservoir should be drained regularly to remove accumulated moisture and oil. Technician B says an automatic drain valve can replace manual draining if it is functioning. Who is correct?
Choose one answer below.
A
A only
✓
B
B only
✓
C
Neither A nor B
✓
D
Both A and B
✓
QUESTION 13 / 25
What component controls air delivery to the front service brake chambers in proportion to brake pedal travel?
Choose one answer below.
A
The primary (front) section of the dual treadle (foot) valve
✓
B
The governor
✓
C
The spring brake control valve
✓
D
The air dryer purge valve
✓
QUESTION 14 / 25
A relay valve is used on the rear axle of a school bus mainly to:
Choose one answer below.
A
Increase reservoir pressure above governor cut-out
✓
B
Speed brake application and release by supplying air to the rear chambers from a nearby reservoir using a control signal
✓
C
Limit pushrod stroke as the linings wear
✓
D
Warn the driver of low air pressure
✓
QUESTION 15 / 25
During a brake application on a school bus, the rear brakes apply noticeably slower than the front brakes and release slowly. Which component is the MOST likely cause?
Choose one answer below.
A
A worn front brake lining
✓
B
A clogged air dryer cartridge
✓
C
A defective rear relay valve
✓
D
A loose alternator belt
✓
QUESTION 16 / 25
The quick-release valve on the front axle of a school bus performs which function?
Choose one answer below.
A
Delivers air to the spring brakes during parking
✓
B
Controls compressor cut-in and cut-out
✓
C
Removes moisture from the supply reservoir
✓
D
Rapidly exhausts air from the front brake chambers when the driver releases the brake pedal
✓
QUESTION 17 / 25
FMVSS 121 sets timing requirements for air brake actuation. The brake application (build) time at the chamber farthest from the treadle valve must generally be:
Choose one answer below.
A
No greater than 0.45 second to reach 60 psi
✓
B
No greater than 2 seconds to reach 60 psi
✓
C
No greater than 5 seconds to reach full pressure
✓
D
Unregulated for school buses
✓
QUESTION 18 / 25
A school bus has a slow brake release at all wheels after the driver lifts off the pedal. Reservoir pressure and build are normal. Which is the MOST likely cause?
Choose one answer below.
A
An undersized compressor
✓
B
A treadle valve that is not fully exhausting the application air
✓
C
A saturated air dryer desiccant
✓
D
A low governor cut-in setting
✓
QUESTION 19 / 25
Technician A says a dual treadle valve provides two separate air delivery circuits so a failure in one circuit still leaves braking on the other. Technician B says the primary and secondary circuits typically serve different axles. Who is correct?
Choose one answer below.
A
A only
✓
B
B only
✓
C
Both A and B
✓
D
Neither A nor B
✓
QUESTION 20 / 25
A double check valve in an air brake system is used to:
Choose one answer below.
A
Drain moisture from the supply tank
✓
B
Reduce pressure to the front chambers
✓
C
Warn the driver of a circuit failure
✓
D
Select the higher of two air pressure sources to supply a circuit or device
✓
QUESTION 21 / 25
A bobtail (or front axle limiting) proportioning function on some buses is used to:
Choose one answer below.
A
Reduce front brake application pressure under light/empty conditions to limit front-wheel lockup
✓
B
Increase rear brake pressure during hard stops
✓
C
Bypass the relay valve at low speed
✓
D
Exhaust the spring brakes faster
✓
QUESTION 22 / 25
When testing service brake apply timing, a technician notices excessive lag at the rear chambers. The reservoir and treadle valve are good. Which is the MOST likely cause?
Choose one answer below.
A
A weak low-pressure warning switch
✓
B
A kinked or restricted air line or a sluggish relay valve at the rear
✓
C
A loose battery cable
✓
D
An over-adjusted slack adjuster
✓
QUESTION 23 / 25
The stop lamp switch on most air-braked school buses is operated by:
Choose one answer below.
A
Mechanical movement of the brake pedal arm only
✓
B
The parking brake control valve
✓
C
Air pressure in the service application circuit
✓
D
The ABS modulator
✓
QUESTION 24 / 25
A school bus exhibits a hissing air leak at a brake chamber only when the service brakes are applied. The leak stops when the brakes are released. The MOST likely cause is:
Choose one answer below.
A
A failed spring brake power spring
✓
B
A worn wheel bearing
✓
C
A leaking governor
✓
D
A ruptured or pinched service brake chamber diaphragm
✓
QUESTION 25 / 25
Technician A says the secondary circuit of a dual air system can be tested by bleeding off the primary reservoir and confirming the secondary still applies its brakes. Technician B says both circuits should hold pressure independently with the engine off. Who is correct?
Choose one answer below.
A
Both A and B
✓
B
A only
✓
C
B only
✓
D
Neither A nor B
✓
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