Figure 30-7. Coil Spring and Control Rod Drive.
driving thrust is absorbed and transmitted through control
stresses that occur during braking. To resist these
rods. The control rods, four in all, also are used to
stresses, as well as those resulting from impacts
maintain the rear axle housing alinement to the frame.
experienced during travel, and still maintain reasonable
Two of the rods are mounted below the centerline of the
wheel alinement and directional stability, the dead front
axle, toward the outside of the rear axle housing and
axle usually is attached to the frame by means of rather
attached to the frame with bushings in the front. The
stiff semielliptic leaf springs. These springs produce a
remaining two are mounted inboard, above the centerline
harsh ride and limit the vehicle speed over irregular
of the axle. As the vehicle accelerates, the axle housing
terrain. Softer springs may be employed, in which case
will try to wind up, the upper control arms will be under
tension, and the lower arms will be in compression,
by separate linkages or other mechanisms.
delivering the driving force to the frame. Under braking
To permit steering, the dead front axles are equipped
conditions, the opposite happens; the upper control arms
with pivoting wheel spindles. The axles are usually i-
are in compression and the lower arms are in tension,
sections of drop-forged alloy steel. The unsprung mass
holding the body back.
may be reduced, and the torque-resistance properties
e. Dead Front Axle. The dead front axle (fig. 30-8)
improved, by using more expensive tubular axles of
supports the vehicle weight and resists the torsional