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FRONT AXLE ASSEMBLY
(Master Conventional
1/2- and 1 1/2-Ton Trucks and Standard Models.)
Construction
The front axle used in the Master Conventional V2-ton and 1M-ton
trucks and Standard models is known as the reverse Elliot type.
It is a steel drop-forging with the spring seats forged integral
with the "I" beam. The "I" beam is heat-treated
for extreme toughness and is machined to very close limits.
The king pin is slotted and held in position by a tapered pin which
is drawn tightly into the slot by a lock washer and nut. The holes
at each end of the "I" beam are bored at a slight angle
to permit the king pin to tilt inward at the top. This inward tilt
is called king pin inclination.
The steering knuckle is mounted to the front axle, by means of
this king pin and rides on a ball bearing which makes steering
easy.
The brake flange plate is securely bolted to the steering knuckles
and carries the brake shoes and their cam operating levers. The
steering knuckle arms are also bolted to the steering knuckle and
are connected with each other by the tie rod. The tie rod is the
adjustable type which is attached to the knuckle arms and controls
the amount of for-gather or toe-in of the front wheels.
The third arm is forged integral with the left knuckle and is connected
to the pitman arm through the steering connecting rod.
A caster shim or "I" beam spacer is inserted between
the front springs and the front axle. The installation of this
shim controls the amount the top of the axle inclines rear-ward.
This rear-ward tilt of the axle gives the front wheels their caster.
The front wheel spindles, which are forged integral with the steering
knuckles, are tilted down-ward at their outer ends, thus causing
the front wheels to be farther apart at the top than they are at
the bottom. This slight angular position of the front wheels is
called camber.
The steering knuckle arms are installed on the knuckles at an angle,
permitting the front wheels to toe-out when making turns. This
set up is necessary due to the fact that in turning curves, each
wheel must travel in a different arc. This toe-out on curves is
known as steering geometry.
93
These five front end factors are built into the axle and must be
in proper relation to each other to prevent steering faults and
excessive tire wear.
Caster
Caster is the amount in degrees of the back-ward tilt of the axle
and king pin. See Fig. 201.
Fig. 201— Caster Angle
A car without caster would lack steering stability and would tend
to wander over the road.
Unequal caster shows itself in the tendency of the car to pull
to the right or left. This condition comes about through the axle
having been twisted so that there is a greater amount of caster
in one king pin than in the other. The direction in which the car
will tend to pull is towards the side with less caster. Suppose
that an accident has put a twist into the front axle so that the
left side is zero caster, while the right side is castered backward
five or six degrees, the right wheel will have a strong tendency
to turn inward, pulling the car to left.
Axles having no caster result in a car that is difficult to steer,
that tends to pull to the right or left and will turn a corner
easily but is hard to straighten out at the end of the curve.
