The Washington herald., 1918-09-29
SEEKS BETTER
TRUCK AXLES
Evolution of Rear System
Still Undergoes Constant
Experiments.

No other vital part of a motor truck
has given engineers as much trouble
as the rear axle. This is due to the
many different kinds Of stress to
which rear axles are subjected, as
we'll as to the fact that the rear axle
is the first part of the truck to re-
ceiye abuse due principally to lack
OF attention.
Engineers have computed the
stresses and strains and have en-
deavored by various means TO make
allowances for them, both through
the size and quality OF the material
used. They seemed to have been
more successful in the early days
than they were a few years later
when 1t was necessary to change the
types OF drive.
When the first rear axles were built
for passenger ears, the power was
transmitted through a bevel gear and
the jackshaft was enclosed in the
load-carrying housing of the rear
axle. Because Of the light loads car
ried in passenger cars. this method of
construction was satisfactory. When
it came TO putting a rear axle under
a truck for the purpose Of carrying a
load of from one to three tons, how
ever. the engineering problem was
decidedly different.
Difficulty With Chains.
The first solution given by engineers
was a solid load-caTrying dead axle
with the power transmitted by means
OF chains and sprockets from a
driveshaft mounted well forward of
the wheels. This type was very sue
cessful so far as the load carrying
was concerned. but the wear on the
exposed chains, due to mud and dirt,
caused them to wear out rapidly and
break at critical moments. Outside of
causing many accidents, these break
ing chains were a continual source OF
annoyance and delay and so it was
found necessary to discard that form
OF drive.
The next solution was copied from
passenger cars. In the new type of
rear axle tiIe gear ratio OF the bevel
gears instead of being to l, as was
the custom in passenger cars. had to
be increased to to l because of the
great pulling power necessary to
move heavy loads. 1t was, therefore.
necessary to greatly increase the size
Of the gear on the axle which in
turn greatly reduced the road clear
ance. This developed into what is
known as the worm gear. which is
quite similar TO the old form of pas
senger car drive.
With this type Of axle, 1t was again
necessary for the axle housing to
carry the entire weight of both the
enormous weight OF heavy steel was
necessary to make the housing sus-
tain the heavy loads.
Ratio for Weights.
Engineers estimate that load of
one pound of inspiring weight, which
IS a weight directly on the axle and
rot allowed the benefit OF spring sus-
pension. is equivalent to nine pounds
on the truck.
The combination of this extremely
heavy rear axle. and the fact that, to
obtain the proper gear reduction, it
waG necessary to greatly decrease the
mount OF road clearance. made this
tpc Of axle generally unsatisfactory,
particularly for trucks in the one
10 twO-ton class. This heavy type of
rear axle was extremely destructive
to tires.
The internal gear drive rear axle
rs used on the Fulton motor truck Is
the latest and probably the final So
lutiOn Of the great problem that has
HCen confronting engineers since the
Grst building Of motor trucks. The
Fulton type OF internal gear drive has
all of the advantages of the former
chain drive, without any of its dis
advantages, and in addition to this
1t gives a maximum road clearance
with a minimum of weight
President Melhuish, Of that COM
pany. has said: I'VE keep a corps of
engineers constantly experimenting
for real Improvements in motor
truck design"