AXLE CASINGS
BANJO TYPE
SPLIT CASING
CARRIER
FINAL DRIVE
FUNCTIONS
Provides the final gear reduction to increase
the available torque.
Transmits the drive through an angle of 90°
The actual gear ratio is calculated by dividing
the number of teeth on the crown wheel by
the number of teeth on the pinion.
Gear ratio = no. of teeth on the crown wheel
no. of teeth on the pinion.
Gear ratio = Driven
Driver
TYPES OF FINAL DRIVE
Straight bevel
Straight cut bevel teeth machined onto both
the crown wheel and the pinion.
DISADVANTAGES OF STRAIGHT
BEVEL
The drive is noisy
Only one pair of teeth is in contact at any
one time, limiting the amount of torque that
can be transmitted.
SPIRAL BEVEL
Spiral bevel drives have teeth inclined
at an angle.
Advantages
More than one pair of teeth are
meshing with each other at any
one time. This enables the gears
to take a higher loading.
The drive is quieter in operation.
HYPOID FINAL DRIVE
This is the type of bevel drive
most likely to be found on
current vehicles. One of its
main features is that the
centre line axis of the pinion
is offset relative to the
centreline axis of the crown
wheel.
Due to this offset, as the
mating parts rotate, the
teeth are subjected to a
higher pressure. A special
type of extreme ( EP )
lubricating oil must be
used.
The pinion is 1/3 larger and
stronger than the spiral
bevel type. Failure due to
breakage is rare.
WORM AND WHEEL DRIVE
the drive consists of a spiral
shaped worm and a toothed
wheel.
Materials used :
Worm : case - hardened
steel
Wheel : phosphor bronze
DISADVANTAGES
Although this final drive
provides a larger gear
reduction, the materials
used in its construction
are very expensive. This
restricts its use to heavy
goods vehicles and buses.
DOUBLE REDUCTION FINAL
DRIVE
Used on earth moving equipment
and very heavy commercial
vehicles.
1st stage gear reduction : crown
wheel & pinion.
2nd stage gear reduction : helical
reduction gears, which reduce the
speed and increase the torque
again.
DIFFERENTIAL UNIT
DIFFERENTIAL UNIT
Purpose :
Enables 2 drive shafts to be
driven at different speeds
but with equal torque.
FUNCTION
Allows the outer wheel to turn
faster than the inner wheel
during cornering
OPERATION OF A DIFFERENTIAL
UNIT
When the gears are engaged,
the engine rotates the crown
wheel together with the
differential housing. If both
road wheels have equal rolling
resistance, neither sun gear
can turn more easily that the
other.
CONTINUED......
this prevents the planet
wheels from rotating: the
whole assembly rotates
together.
Differential unit is not in
operation.
DURING CORNERING
Inner wheel turns slower than
the outer wheel due to
resistance.
The planet wheels turn on their
shaft rotating around the
stationary sun gear
The other sun gear is driven
twice as fast.
DIFFERENTIAL LOCK
WHAT IS IT ?
It is a mechanical device
that, when fitted to a
differential unit, prevents
the driving wheels from
rotating at different
speeds.
OPERATION
A dog clutch is moved
electrically by a solenoid.
Engagement :
Sliding a dog clutch meshes
with a set of dog teeth on
the differential cage.
CONTINUED......
the sun gear and rear wheel
connected to this sun gear is
made to turn at the same
speed as this cage.
Locking one sun gear to the
cage in this way ensures that
the other sun gear also turns at
the same speed.
FINAL DRIVE ADJUSTMENTS
Pinionbearing preload
Backlash
Tooth pattern / contact
PINION BEARING PRELOADING
What is pinion bearing pre-loading
Forcing the bearings together by adjustment to
the position occupied by the bearings when the
unit is under full load
1. Using a rigid spacer
Fully tighten the pinion nut.
Measure the torque using a spring balance. If
it is found to be incorrect, either add or
remove shims
2. Using a collapsible spacer
With the pinion bearings and seal in position,
tighten the nut to specifications. This action
allows the spacer to collapse, allowing the pre-
load to be set in one operation.
BACKLASH
Setting the clearance between the pinion
teeth and the crown wheel teeth using a dial
test indicator.
Move the crown wheel toward or away from
the pinion using adjusting nuts provided behind
the carrier bearings.
when shims are used, adjustment is achieved
by increasing the shim thickness on each side
of the crown wheel. The shims are added after
the backlash has been set.
TOOTH PATTERN
Paint about 3 crown wheel teeth with a light
coating of mechanics’ blue.
Using a wrench, turn the pinion shaft in the
normal forward drive direction while creating a
drag on the crown wheel. The drive pattern
should be fairly well placed on the tooth.
TOOTH MARKINGS
diagrams
PINION HEIGHT
Pinion height or depth using special tools
provided by the manufacturer to establish
the centre of the carrier bearings.
With the pinion gear in position, measure the
depth from the centre- line of the carrier
bearings to the face of the pinion gear.
N.B
Pinion depth is controlled by placing shims
between the pinion gear and bearing.
