Advanced Automotive Fault Diagnosis

Rear bearings
Stub axle
Solid mounted to the suspension arm, this 
stub axle fits in the centre of the two 
bearings
Seal
Keeps out dirt and water, and keeps in the 
grease lubrication
Inner bearing
Supports the weight of the vehicle at the 
rear, when still or moving. Ball bearings are
used for most vehicles with specially shaped
tracks for the balls. This is so the bearings
can stand side loads when cornering
Spacer
To ensure the correct spacing and pressure 
between the two bearings
Drum
For the brakes and attachment of the wheel
Outer bearing
As for inner bearing
Washer
The heavy washer acts as a face for the nut 
to screw against
Castle nut and 
Holds all parts in position securely. With 
split pin
this type of bearing, no adjustment is made
because both bearings are clamped on to the
spacer. Some older cars use tapered 
bearings and adjustment is very important
Grease 
Retains grease, but should not be over 
retainer cap
packed. Also keeps out the dirt and water
10.1.4 Final drive and differential
Because of the speed at which an engine runs, and
in order to produce enough torque at the road
wheels, a fixed gear reduction is required. This is
known as the final drive, and consists of just two
gears. These are fitted after the output of the gear-
box, on front wheel drive, or in the rear axle after
the propshaft on rear wheel drive vehicles. The
gears also turn the drive through ninety degrees on
rear wheel drive vehicles. The ratio is normally
about 4:1; in other words when the gearbox out-
put is turning at 4000 rev/min the wheels will turn
at 1000 rev/min.
Many cars now have a transverse engine, which
drives the front wheels. The power of the engine
therefore does not have to be carried through a right
angle to the drive wheels. The final drive contains
ordinary reducing gears rather than bevel gears.
The differential is a set of gears that divide the
torque evenly between the two drive wheels. The
differential also allows one wheel to rotate faster
than the other does when necessary. When a car
goes around a corner, the outside drive wheel
travels further than the inside one. The outside
wheel must therefore rotate faster than the inside
one to cover the greater distance in the same time.
Some higher performance vehicles use limited
slip differentials. The clutch plates are connected
to the two output shafts and hence if controlled
will in turn control the amount of slip. This can be
used to counteract the effect of one wheel losing
traction when high power is applied.
Differential locks are used on many off-road
type vehicles. A simple dog clutch or similar
device prevents the differential action. This allows
far better traction on slippery surfaces.

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