302B

Question 1

Identify five (5) functions of an off-road suspension system as outlined in this
module

Answer 1

a) Have a specific load carrying capacity for each particular application.
b) Absorb, and transmit torque loads (drive and braking) to the vehicle frame.
c) Respond quickly to changes in terrain so that the tires remain in full contact
with the ground.
d) Provide a cushioning effect to increase operator comfort and protect the
vehicle and load from undue stresses during operation.
e) Position the axle assembly accurately in relation to the driveline, on
mechanical drive machines.

Question 2

A tractor scraper can be equipped with either a basic hitch system or a cushion hitch
system.T/F

Answer 2

true

Question 3

A cushion hitch system acts as a connection device, a suspension device and as part
of the steering system.T/F

Answer 3

true

Question 4

The tractor bracket is attached to the tractor while the scraper hitch assembly is
attached to the scraper.T/F

Answer 4

true;

Question 5

On a cushion hitch assembly, identify the major component that is attached to the rod
end of the load cylinder.

Answer 5

The rod end of the load cylinder is attached to the scraper hitch portion of the cushion
hitch assembly.

Question 6

On a cushion hitch assembly, identify the major component that is attached to the
head end of the load cylinder.

Answer 6

The head end of the load cylinder is attached to the tractor bracket assembly that is
connected to the tractor section.

Question 7

Identify the two (2) major types of suspension systems used with off-road haul
trucks.

Answer 7

a) The rubber block type of suspension system.

b) The hydropneumatic type of suspension system.

Question 8

The cushion hitch system is automatic and cannot be controlled by the machine
operator. T/F

Answer 8

false;

Question 9

Explain how the load cylinder and accumulator operate as a unit when the cushion
ride feature is selected and the ground is rough.

Answer 9

As the machine moves over uneven ground, with the cushion ride feature selected, oil
from the load cylinder moves into the accumulator

Question 10

The hydraulic pump pressure servo valve senses hydraulic pump output pressure and
directs hydraulic pressure to the hydraulic pump control piston. The device that is
operated by the hydraulic pump control piston is the:

Answer 10

swashplate.

Question 11

The hydraulic system does not have to be depressurized before hydraulic system
components are removed, opened, adjusted or loosened.T/F

Answer 11

false;

Question 12

The performance of a hydraulic pump can be determined in part from the results of a
percent of flow loss test.T/F

Answer 12

true

Question 13

The condition of an axial piston type of hydraulic pump can be determined in part by the results of an oil leakage test.T/F

Answer 13

true

Question 14

Identify the gas that is used in the cushion hitch accumulator(s).

Answer 14

Dry nitrogen gas is the only gas used in cushion hitch accumulators.

Question 15

When you are charging or testing cushion hitch accumulators, you must:

a) wear safety glasses and gloves during the procedure.
b) follow the specific instructions provided by the particular manufacturer of the test equipment.
c) consult a temperature compensating chart for the particular type of accumulator.
d) conduct the charging or testing procedure in a specific sequence of steps.

Answer 15

do all of the above.

Question 16

A haul truck may use rubber block and/or hydropneumatic components in a
suspension system.T/F

Answer 16

true

Question 17

Explain the basic operation of a hydropneumatic suspension cylinder as the truck moves over rough terrain.

Answer 17

When a truck moves over a bump on the ground the rod and piston assembly move
upward in the cylinder bore. Nitrogen gas above the piston is compressed to a greater
degree than its preset charge.

Question 18

Explain the two (2) functions of the hydropneumatic cylinders used on the front of a large haul truck.

Answer 18

. a) One function of a front mounted hydropneumatic cylinder assembly is to control
vertical movements as the truck moves over uneven ground.
b) Another function of a front mounted hydropneumatic cylinder assembly is to act
as a portion of the steering system (the rod mounts in the steering spindle).

Question 19

The grease fittings on the rear hydropneumatic suspension cylinder bearings are typically lubricated at a central lubrication point.T/F

Answer 19

true

Question 20

Identify two (2) functions of the charging valve used on a hydrair suspension cylinder.

Answer 20

a) Testing the charge pressure of the nitrogen gas in the hydrair cylinder.
b) Charging the nitrogen gas to the proper pressure as required by the size of the
cylinder and the truck application.

Question 21

Explain the purpose of a payload pressure sensing valve, as used on some suspension
cylinders.

Answer 21

The payload pressure sensing valve senses hydrair nitrogen gas pressure and converts
that reading into an electrical signal. That signal is sent to the electronic monitoring
system where it is converted into a weight measurement. This helps to determine the
operating performance of the truck during a work shift

Question 22

Suspension cylinder seals are located within the cylinder assembly. They seal the
piston at the cylinder wall.T/F

Answer 22

true

Question 23

Whenever a haul truck body section must be raised, or whenever the articulated
steering must be secured, proper safety devices must be used.T/F

Answer 23

true

Question 24

Identify four (4) of the conditions under which you would inspect and/or service a
hydropneumatic suspension cylinder.
a) A fault code on the electronic monitoring system indicates that the nitrogen
charge pressure in a cylinder is low.
b) Most of the chrome on the exterior of the strut rod has been removed by the
wiper seal during normal operation.
c) The cylinder shows signs of oil or nitrogen gas leakage.
d) The ride is harsh.
e) The strut rod is fully extended when the truck is empty

Answer 24

Any four (4) of the following are correct.