When maximum traction is required such as for
pulling through deep sand, mud or snow, the lockout
control on dash is operated to engage the power divider
lock. This activates the shift fork shaft and fork in power
divider to lock up the inter-axle differential and provide
positive drive to both forward and rear axle units.
The lockout mechanism must be engaged only when
the truck is standing still. It should be kept engaged only
as long as positive traction is required. Continuous
unnecessary engagement will result in excessive tire
wear and may damage the axles.
The power divider lockout is controlled by either a
valve or switch on the vehicle instrument panel. A "tell-
tale" warning light is also provided on instrument panel to
indicate when power divider lock is engaged.
Three different kinds of power shift systems are
used to actuate the power divider lock. These systems
are covered in paragraphs which follow.
ELECTRIC SHIFT SYSTEM
The electric shift system consists of an electric
powered motor unit mounted on the forward rear axle
with a control switch on dash.
For complete information on the electric shift system
(Maintenance, Trouble Shooting, Rebuild, etc. See
REAR AXLES CTS-4041 in the Service Manual).
VACUUM SHIFT SYSTEM
The vacuum shift system consists of a vacuum
power unit mounted on the forward rear axle with a
control valve located on the instrument panel. The
power source for the vacuum shift system is vacuum
from the engine intake manifold for gasoline engines or a
vacuum pump for diesel engines. If either the vacuum
power unit or vacuum control valve are defective they
must be replaced.
AIR SHIFT SYSTEM
The air shift system consists of an air power cylinder
mounted on the forward rear axle with an air control
valve on the instrument panel. The power divider lock is
disengaged by air pressure and spring controlled for
engagement ("lock in").
When the PDL (Power Divider Lock) control is
placed in the "lock" position air in the system is
exhausted and the PDL will shift to the "lock" mode.
When the PDL control is placed in the "unlock"
position, air pressure will hold the PDL in the disengaged
The air control valve, control cylinder, hoses and
pipe connections of air control systems should be
inspected periodically for leakage and other repairs. At
time of axle overhaul, control cylinder and control valve
should be inspected carefully and worn or damaged
Axle failure can also be attributed to the axle shaft.
For this reason it is most important that shafts be
installed properly, be of correct size and lengths for
splines to engage fully and be kept free from runout or
The axle housing is of one piece construction with an
opening in the center for mounting the diff carrier. A
flange is welded to the outer ends of the axle housing for
mounting the brake backing plates. A bent axle housing
can be the cause of early axle failure and whenever an
axle is rebuilt this condition should always be checked
before going ahead with the assembly.
The condition of axle housing cover weld should also
be checked. If cover weld is cracked, oil seepage from
housing can occur. Re-welding of housing cover is
permitted providing special cleaning precautions and
recommended welding procedures are observed.
Procedure for repairing cracked weld or leaking
housing cover is as follows:
Drain differential and remove diff carrier assembly.
Clean lube from inside of housing and burn
remaining lube from inside with torch.
Clean residual lube from housing with solvent.
Grind or air arc cracked weld from outside of cover
weld to base metal.
Weld three passes around outside of cover using
1/8" Spec. No. E7016 Weld Rod and suppliers
recommended amperage and voltage. Thoroughly
clean weld area between passes.
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