this assembly a true full-floating axle, but nevertheless,
it is called a floating axle. A true full-floating axle
transmits only turning effort or torque.
Wheels attached to live axles are the driving wheels.
The number of wheels and number of driving wheels is
sometimes used to identify equipment. You, as a
mechanic, may identify a truck by the gasoline or diesel
engine that provides the power. Then again, you may
refer to it as a bogie drive.
Wheels attached to the outside of the driving wheels
make up DUAL WHEELS. Dual wheels give additional
traction to the driving wheels and distribute the weight
of the vehicle over a greater area of road surface. They
are considered as single wheels in describing vehicles;
for example, a 4 x 2 could be a passenger car or a truck
having four wheels with two of them driving. A 4 x 4
indicates a vehicle having four wheels with all four
driving. In some cases, these vehicles will have dual
wheels in the rear. You would describe such a vehicle as
a 4 x 4 with dual wheels.
A 6 x 4 truck, although having dual wheels in the
rear, is identified by six wheels, four of them driving.
Actually, the truck has ten wheels but the four wheels
attached to the driving wheels could be removed without
changing the identity of the truck. If the front wheels of
this truck were driven by a live axle, it would be called
a 6 x 6.
The tracks on tracklaying vehicles are driven in
much the same manner as wheels on wheeled vehicles.
Sprockets instead of wheels are driven by live axles to
move the tracks on the rollers. These vehicles are
identified as either full-track, half-track or vehicles that
can be converted.
Full-track vehicles are entirely supported, driven,
and steered by two tracks that replace all wheels.
SERVICE AND MAINTENANCE
There are very few adjustments to be made in power
trains during normal operation. Most of your duties
concerned with power trains will be limited to
preventive maintenance. You will be working with the
disassembly, repair, and reassembly of transmissions,
rear axles, and propeller shaft assemblies when they
break down. You will also inspect these units for
indications of major repairs needed. Major repairs can
be reduced by proper lubrication and periodic inspection
of gear cases, propeller shafts, and wheel bearings.
Proper lubrication depends upon the use of the right
kind of lubricant which must be put in the right places
in the amount specified by the LUBRICATION
CHARTS. The charts, provided with the vehicle, will
also show what units in the power train will require
lubrication, and where they are located. These units are
similar to the ones described and illustrated in this
In checking the level of the lubricant in GEAR
CASES and before you add oil, keep these two
important points in mind: first, always carefully wipe
the dirt away from around the inspection plugs and then
use the proper size wrench to remove and tighten them.
A wrench too large will round the corners and prevent
proper tightening of the plug. For the same reason, never
use a pipe wrench or a pair of pliers for removing plugs.
Second, be sure the level of the lubricant is right-usually
just below or on a level with the bottom of the inspection
hole. Before checking the level, allow the vehicle to
stand for a while on a level surface so the oil can cool
and find its own level. Oil heated and churned by
revolving gears expands and forms bubbles. Although
too little oil in the gearboxes is responsible for many
failures of the power train, do not add too much gear
lubricant. Too much oil results in extra maintenance.
Excessive oil or grease can find its way past the oil
seals or gear cases. It maybe forced out of a transmission
into the clutch housing and result in a slipping clutch; or
it may get by the rear wheel bearings from the
differential housing to cause brakes to slip or grab. In
either case, you will have extra work to do. Always clean
differential and live axle housing vents to prevent
pressure buildup (caused by heat), which can result in
UNIVERSAL JOINTS and SLIP JOINTS at the
ends of propeller shafts are to be lubricated if fittings are
provided. The same holds true for WHEEL
BEARINGS. Some of these joints and bearings are
packed with grease when assembled; others have grease
fittings or small plugs with screwdriver slots that can be
removed for inserting grease fittings. Do not remove
these plugs until you consult the manual for instructions.
Some passenger cars and trucks have a leather boot
or shoe covering the universal and slip joint. The boot
prevents grease from being thrown from the joint and it
also keeps dirt from mixing with the grease. A mixture