Exam (elaborations)
Transit Bus ASE Test Preparation - (Test H4) Brake Test - part 2
- Course
- Institution
Transit Bus ASE Test Preparation - (Test H4) Brake Test - part 2
[Show more]
Seller
Follow
lydiaomutho
Content preview
Transit Bus ASE Test Preparation - (TestH4) Brake Test - part 2
A bus equipped with air brakes completely loses the primary air reservoir. Under these
conditions, how is the relay section of a dual-circuit, air brake foot valve actuated?
A. Air pressure from the secondary reservoir
B. Air pressure from the primary section of the foot valve
C. Mechanically, by direct foot pressure
D. Mechanically, by the primary piston - ANS-Answer D is correct. The relay piston is
actuated mechanically by the primary piston in the event of loss of primary
circuit air. The foot pedal acts on the primary piston which drives it down until it contacts
the relay piston to actuate the
secondary circuit.
A bus is diagnosed with an active modulator valve code. A technician first should:
A. check for parts availability before putting the bus out of service.
B. clear codes and road test.
C. clean contacts and check specified solenoid resistance.
D. check continuity between modulator valve and the ECU. - ANS-Answer C is correct.
You must first verify if the modulator valve solenoids are defective. Cleaning the
solenoid contacts
and "ohm out" the solenoids is the right diagnostic procedure. If the modulator solenoids
are found to be in good condition, checking continuity between the modulator valve and
ECU is the next diagnostic step; therefore, Answer D is wrong. Answer A is wrong. You
must verify a faulty valve before part replacement. Answer B is wrong. You cannot
clear an active code/fault.
A decelerometer like the one in the figure is being used to check the performance of a
pre-ABS equipped air brake system. Technician A says the bus should be driven to 20
mph in a safe area and the brakes applied until the wheels lock up or skid. Technician B
says the bus should be driven to 20 mph in a safe area and the brakes should be
applied quickly and firmly but not to the point of wheel lock up. Who is correct?
A. A only
B. B only
C. Both A and B
D. Neither A nor B - ANS-Answer B is correct. When performing a decelerometer test
you are testing the stopping power of the brake system.
,Most manufacturers recommend accelerating the vehicle to 20 mph and applying the
brakes in a firm application on a dry, level surface, free of gravel, debris and other
obstacles. Skidding should be avoided as it can skew the results. The best coefficient of
friction is obtained just before the point of wheel lock up or skidding. This takes into
account why ABS are now mandated on heavy duty transit vehicles.
A driver complains ofdragging brakes in an air brake equipped bus. Technician A says a
leaking hold-off diaphragm could cause the problem. Technician B says a broken return
spring in the service chamber could be the cause. Who is right?
A. A only
B. B only
C. Both A and B
D. Neither A nor B - ANS-Answer C is correct. When a hold-off diaphragm leaks, the
result can be insufficient air pressure to prevent the power
spring from loading the chamber pushrod applying brake pressure. So Technician A is
right. Technician B is also right; a broken or weak return spring can cause brake drag.
A technician is performing an air pressure balance test between the front axle and rear
axle of a bus. Where should the pressure gauges be located?
A. At the brake application valve
B. At two corresponding relay valves
C. At each of the corresponding reservoirs
D. At two corresponding brake chambers - ANS-Answer D is correct. When performing
an air pressure balance test the test gauges should be located at two corresponding
brake chambers because the pressure is important but so is the timing of the delivery.
The distance the air has to travel and the condition of the lines and fittings will affect
this, so the gauges should be as close to the brake assemblies as possible.
A transit vehicle equipped with an automatic air drier is found to have excessive
moisture and oil contamination when the air tanks are drained on a preventive
maintenance inspection. Technician A says this could be caused by a defective air drier
unit. Technician B says the air governor could be defective. Who is correct?
A. A only
B. B only
C. Both A and B
D. Neither A nor B - ANS-Answer C is correct. Both Technicians are correct. Technician
A is correct because the purpose of the air drier is to
remove the moisture and some passed oil. A defective unit could definitely cause this
problem. Technician B is correct
, because most air driers use the governors unloader circuit signal (or air pressure) to
signal the air drier when to purge
and expel the contaminants.
All of the following are common brake testers EXCEPT:
A. performance-based brake testers.
B. hydraulic tester.
C. electronic tester
D. mechanical tester - ANS-Answer B is correct. A PBBT measures brake forces at
each wheel. Electronic testers, such as Vericom and Fraser,
sense rate of speed change and then uses this data to calculate stopping distances and
a mechanical tester such as Tapley
meter is a pendulum device that measures deceleration but only saves a value that
represents the maximum deceleration
reached during the stop.
All of the following are part of an air compressor EXCEPT:
A. piston rings.
B. the crankshaft.
C. the discharge valve.
D. the governor. - ANS-Answer D is correct. An air compressor has pistons, a
crankshaft, and a discharge valve. The governor is always a separate component that
may be mounted on the compressor or remotely.
All of the following are parts of an air disc brake assembly EXCEPT:
A. cam actuator.
B. torque plates.
C. calipers.
D. rotors. - ANS-Answer A is correct. There is no cam actuator used on an air disc
brake system.
All of the following can be causes of brake torque imbalance EXCEPT:
A. oil-soaked linings.
B. nonuniform adjustment.
C. nonuniform chamber sizes.
D. an overloaded vehicle. - ANS-Answer D is correct. All of the answers relate to brake
torque imbalance problems except for a vehicle overload condition.
While overload might tax brake system potential, it would not in itself cause brake
torque imbalance.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller lydiaomutho. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.99. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
78252 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now