the equipment is moving forward or backward. This
design lessens rolling resistance in soft ground, because
one set of tires prepares a path for the other set.
Additionally, this design provides maximum control of
the direction of the load. Also, it enables the equipment
to be held on a straight course and permits short turns in
proportion to the maximum angle of the wheels.
In crab steering, both sets of wheels are turned in
the same direction. If both sets of wheels are turned at
the same angle, the machine moves in a straight line at
an angle to its centerline. Results can be obtained from
either four-wheel steering or crab steering by using
different turning angles on independently controlled
front-and-rear wheels.
SUSPENSION SYSTEMS
A suspension system anchors and suspends the
wheels or tracks from the frame with springs, as shown
in figure 3-5. It supports the weight and allows the
vehicle to be driven under varying loads and speed
conditions over bumpy roads and rough terrain without
great risk of damage.
miles. The spring assemblies of the suspension system
should be checked regularly to ensure that shackles are
tight and that bushings within the shackles are not
overworn or frozen tight. Occasionally, spraying
lubricating oil on the spring leaves helps to prevent
squeaking at the ends of the spring leaves. Following the
lubrication chart for a particular vehicle, check and
lubricate the front suspension system, including
linkages, kingpins, and ball joints. During your checks
you may find shock absorber bushings worn. If so,
document it and turn it in so the problem can be looked
at. The Construction Mechanic (CM) inspector may
decide the shock absorbers should be replaced.
Some symptoms of suspension troubles in vehicle
operation that should be documented and turned in for
repair are as follows:
. Hard steering
l Vehicle wanders
l Vehicle pulls to one side during normal driving
l Front-wheel shimmy
Although suspension systems are a part of your
l Front-wheel tramps (high-speed shimmy)
prestart and operator maintenance responsibilities, they
usually do not need to be adjusted or replaced for many
l Steering kickback
Figure 3-5.—Front axle suspension system.
3-4
