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Exam 28: Truck Brake Systems

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Question 51

Multiple Choice

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In a typical FMVSS 121 compliant tractor-trailer,when you actuate the trailer hand control valve which circuit supplies air to the trailer service brakes when the system is functioning normally?

A) primary circuit
B) secondary circuit
C) supply circuit
D) park/emergency circuit

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Question 52

Multiple Choice

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Technician A says that the relay section of a dual circuit foot valve is actuated mechanically under normal operation.Technician B says that the primary piston of a foot valve is actuated mechanically under normal operation.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

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Question 53

Multiple Choice

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When the emergency/parking brakes are released on an air-brake equipped highway tractor-trailer combination with a three valve system,which dash control button(s) MUST be depressed before you can move the rig?

When 1000 pounds of linear force is delivered to a 6-inch slack adjuster,how much brake torque is produced at the S-camshaft?

How many anchor pins are used for a pair of S-cam actuated brake shoes?

Technician A says that truck brake shoe edge codes are used as an exact measure of their coefficient of friction.Technician B says that the first letter of an edge code indicates the coefficient of friction of the friction facing when cold.Who is correct?

When secondary circuit signal air is routed to through the trailer service signal circuit,which brake valve is responsible?

Technician A says that air disc brakes have higher mechanical braking efficiencies than S-cam actuated,drum brakes.Technician B says that air disc brakes offer better control than equivalent drum brakes.Who is correct?

What is primarily used to cool air compressors on most truck air brake systems?

Which of the following is another way of describing the parking brake circuit?

Which of the following components functions to control the compressor effective cycles?

When a properly functioning treadle valve is actuated by foot pressure,which of the following will determine what pressure is metered out to actuate the primary and secondary service circuits?

What is the function of a quick-release gladhand when used?

Technician A says that brake chambers convert air pressure into rotary force.Technician B says that slack adjusters convert rotary force into linear force.Who is correct?

Which of the following pressure value ranges are FMVSS-121 compliant governor cut-out pressures?

If the service chamber of a 30/30 spring brake chamber has an application pressure of 50 psi acting on its service diaphragm,how much linear force is delivered to the slack adjuster?

An air brake equipped highway tractor features single dash air pressure gauge with two needles,one green and the other red.What does the red needle display?

Which of the following pressure values are FMVSS-121 compliant for governor cut-out and cut-in pressures?

In what year was FMVSS 121 introduced?

If you have to make an adjustment to air system cut-out pressure,where should the adjustment be made?