Q2-4. How are drive axles secured to an item of
and maintenance. The main disadvantage of coil
springs is that their frictionless action results in too
much pitching of the vehicle. This pitching is
They are encased in a housing
dampened by the action of the shock absorber.
They are bolted to the frame with U-bolts
They are welded to the frame
Figure 2-5, view A, shows how a coil spring is
They are attached by the springs and
mounted. The spring seat and hanger are shaped to fit
the coil ends and hold the spring in place. Spacers
made of rubberized fabric are placed at each end of the
Q2-5. Ensuring grease is forced between the rollers
coil to prevent squeaking. The rubber bumper,
of a wheel bearing is a very important step to
mounted in the spring supporting member, prevents
prevent the bearing from overheating.
metal-to-metal contact when the spring is compressed.
Coil spring systems require torque rods or a stabilizer
shaft to prevent the axle from moving forward and
Springs require very little maintenance; normally
they are changed only when they fail. Leaf springs (fig.
LEARNING OBJECTIVES: Identify the
2-5, view B) present no problem to change. The unit is
normal components of a suspension system.
raised until the tires are off the ground; then jack stands
Identify the springs used on suspension
are placed under the frame. Next, a floor jack is placed
systems. Describe the shock absorbers used on
under the axle, and it is raised until a no-load condition
a suspension system.
is obtained. Then, the bolts or pins holding the spring
in place are removed, the spring is unbolted from the
The suspension systems for support equipment
axle and removed, and the new springs are installed.
differ from most highway-driven vehicles. Most of the
support equipment is not designed to travel over 15 to
Coil springs (fig. 2-5, view A) are replaced in
20 miles per hour, and is only required to move short
about the same manner, but must also be compressed
distances. The normal components of a suspension
b y a s p r i n g c o m p r e s s o r p r i o r t o r e m ova l a n d
system are the springs and shock absorbers. However,
some tow tractors have no rear springs, as the axles are
bolted to the frame. Support equipment with
suspension systems have either leaf or coil springs.
Consult the applicable technical manual before
trying to repair a faulty coil spring--they can be
very dangerous if removed incorrectly.
Springs support the frame above the axle and the
body of the vehicle, as well as the equipment mounted
on the vehicle. They provide a flexible connection
between the wheels and the frame and allow the vehicle
to withstand the shocks of uneven surfaces. The best
Springs alone are not always satisfactory in a
spring is one that absorbs shock rapidly and returns to
vehicle suspension system. A stiff spring gives a hard
its normal position slowly. Since the spring cannot
ride because it does not flex and rebound when the
perform this function alone, it is assisted by a shock
vehicle passes over a bump. On the other hand, a spring
absorber. Very flexible springs allow too much
that is too flexible rebounds too much, and causes the
movement of the frame, while stiff springs do not allow
vehicle to ride rough. Shock absorbers are used to
enough movement. The springs do not actually support
smooth the riding qualities of the vehicle. They prevent
the weight of the wheels and axles. These parts make
excessive jolting of the vehicle by balancing spring
up the unsprung weight of the vehicle, which decreases
stiffness and flexibility. They allow the springs to
the action of the springs. Therefore, the unsprung
return to rest slowly after having been compressed.
weight is kept to a minimum to permit the springs to
Double-acting shock absorbers (fig. 2-6) check spring
support the vehicle frame and load.
compression as well as rebound. Most shock absorbers
used at present are of the double-acting type because
C o i l s p r i n g s ( fi g . 2 - 4 ) a r e u s e d o n m o s t
they permit the use of the more flexible springs.
independent suspension systems because of low cost