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 TM 9-8000
the forward rear axle, and is attached to the forward end
As in the case of rear live axles, the axle housings
of the interaxle drive shaft.
usually are built up, but they may be pressed steel for
light vehicles and single-piece castings for heavy-duty
(2) The power divider is attached to the forward
vehicles. The split-type housing frequently is used. The
end of the gear carrier, which is mounted on the upper
principal difference between front live axles and rear
side of the axle housing. Both forward and rear axles
axles is that in front-wheel drives, provision must be
are driven from the forward drive flange through the
made for steering. In rear driving axles, the axle shafts
power divider by means of a driving cage carrying two
are connected directly to the wheels. Because the front
parallel rows of radial wedges or plungers engaging at
wheels must turn on the steering knuckle pivots, they
their outer ends with internal (female) cams on a cage
usually are driven by the axle shafts through universal
that drives the bevel pinion of the forward rear axle. At
joints (para 28-7) concentric with the steering knuckle
their inner ends, the plungers engage with external
pivots. Figure 29-17 shows the housings of the steering
(male) cams on the interaxle drive shaft, which drives the
knuckle pivots and constant-velocity universal joints, as
bevel pinion of the rear axle. Due to the wedging action
well as the tie rod, brakedrums, hub flanges, and wheel
between the cams and the plungers, they rotate together
mounting studs for a typical front live axle assembly.
with no relative movement, unless running condition
require a differential action.
(2) A type of front-wheel drive that drives the
front wheels through gearing and permits them to steer
(3) Whenever either the forward or the rear
without the use of a universal joint is shown in figure 29-
pair of wheels tends to run ahead of the other pair, due
18. It has been used to a very limited extent. A spiral-
to slippage or uneven road surfaces, there is a relative
bevel pinion keyed to the end of the axle shaft drives the
movement of the external and internal cams, which is
lower half of a double bevel gear on the lower end of the
permitted by the sliding of the radial plungers in the
steering knuckle pivot. The top half of the double gear
driving cage. This restricted movement provides a
meshes with a fourth gear that is integral with the wheel
differential action that divides the driving effort to the two
hub. The gear and hub turn on the steering knuckle.
pairs of wheels to provide the maximum tractive effort.
When the wheels are cramped, the bevel gear on the
The wheel spindles are pressed into the axle housing,
wheel hub rotates around the bevel gear on the steering
and the brake assemblies are carried by integral flanges.
knuckle pivot.
The underslung springs, which tie the two rear axle
housings together in parallel relation, are attached by
(3) Constant-velocity universal joints, used
means of rubber shock insulators set in sockets on the
with front-wheel drives to avoid strain on the steering
bottom of the housing, and retained by caps.
mechanism, are discussed in chapter 28.
m. FourRear-WheelDrives.
(4) A ball-joint torque rod, between the top of
the gear carrier housing and a chassis frame
crossmember, takes the torque conveyed to the axle
(1) Motor vehicles that carry extremely heavy
assembly by the driving and braking.
loads often are equipped with four rear wheels in order to
increase traction and to avoid excessive weight on the
I.
Front Wheel(Steerable) LiveAxle.
rear tires; that is, the weight of the load is divided among
twice as many tires as when only one rear axle is used.
(1) In four- or six-wheel drives, the front wheels
Dual wheels generally are used with this arrangement;
are driven through a driving axle assembly very similar to
therefore, the weight of the rear of the vehicle and load is
a rear axle. It may be of the single or double-reduction
divided among eight tires instead of four.
type. Figure 29-17 shows a usual arrangement of
transfer assembly, propeller shafts, universal joints,
(2) Different spring suspensions are used, but
driving axles, and springs for a four- or six-wheel drive
the bogie is most general. A bogie consists of two axles
vehicle. Front-wheel drives ordinarily are Hotchkiss
joined by a trunnion axle. The trunnion
drives with the front springs pivoted at the rear and
shackled at the front. Axles are of the full-floating type.
29-17
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