2.

Power train
2.1 Clutch system
2.1.1 Purpose, functions, operation and types
2.1.2 Troubleshooting and remedies
2.2 Gear box
2.2.1 Purpose, functions and operation
2.2.2 Manual (sliding mesh, constant mesh, synchro mesh) gear box
2.2.3 Epicyclic gear box
2.2.4 Fluid coupling and torque converter
2.2.5 Automatic gear box
2.2.6 Over drive
2.2.7 Gear box lubrication
2.2.8 Troubleshooting and remedies
2.3 Transfer case
2.3.1 Purpose, functions and operation
2.3.2 Drive: high and low speed
2.3.3 Troubleshooting and remedies
2.4 Universal joint and propeller shaft
2.4.1 Purpose and functions
2.4.2 Types of propeller shaft
2.4.3 Troubleshooting and remedies
2.5 Final drive
2.5.1 Purpose, functions and operation
2.5.2 Differential: components, working, differential lock and lubrication
2.5.3 Back-lash setting
2.5.4 Troubleshooting and remedies
2.6 Axle
2.6.1 Purpose, functions, operation and types
2.6.2 Troubleshooting and remedies
Clutch System Basics and Operation
A clutch is the mechanical device that transfers all power from the
engine into the transmission of a vehicle. Without a properly operating
clutch, power transfer and gear shifting would be very difficult. The
clutch is located between the engine flywheel and the transmission. It is
often housed within the bellhousing to protect it from external
contaminants. Much older vehicles had more of a fully open design. The
first section of this system starts at the flywheel. Connected to the
flywheel is the pressure plate, with the clutch-friction disc between the
two items. On the outside of the pressure plate will be the clutch control
unit, or the throw-out bearing. The throw out bearing is moved by the
use of a clutch fork. The clutch fork is operated by a slave cylinder, and
the slave cylinder is control by the master cylinder ultimately controlled
by the clutch pedal.

Pressure Plate:
 The pressure plate assembly is secured to the flywheel via bolts
connecting the cover stamping to the flywheel. During engagement, the
pressure plate assembly clamps the disc assembly against the flywheel,
transmitting engine power to the transmission. During disengagement,
power flow is interrupted when the pressure plate no longer clamps the
disc against the flywheel. Instead, the pressure plate lifts away from the
flywheel, creating a gap large enough for the disc to disengage from the
flywheel, enabling the driver to shift gears.

Clutch Disc:
The disc assembly is mounted to the input shaft, between the
pressure plate assembly and the flywheel. During engagement, the disc
slides forward on the input shaft and becomes solidly clamped, or
“engaged”, between the flywheel and the pressure plate assembly.
During disengagement, the disc is no longer engaged. Although the
pressure plate assembly and flywheel continue rotating, the input shaft
and disc are no longer being rotated by the engine.

Pilot Bushings:
Pilot bearings and bushings serve as a guide and seat for the
transmission input shaft during engagement and disengagement when
the flywheel and pressure plate assembly turn at speeds different than
the input shaft and disc assembly, the pilot bearing rotates.

Throw-out Bearing:
Release bearings are designed to pivot forward and compress the
pressure plate levers, which disengages the clutch system. Although
release bearings are all designed for the same basic function, they come
in many shapes and sizes because they must work in conjunction with a
variety of actuation systems.
Types of Clutches

1.Friction clutch
1.Single plate clutch
2.Multiplate clutch
1.Wet
2.Dry
3.Cone clutch
1.External
2.Internal
2.Centrifugal Clutch
3.Semi-centrifugal clutch
4.Conical spring clutch or Diaphragm clutch
1.Tapered finger type
2.Crown spring type
5. Dog and spline clutch
6. Electromagnetic clutch
7. Vacuum clutch
8. Hydraulic clutch
9.Overrunning clutch or freewheel unit
Friction clutch
Single Plate Clutch
Single plate clutches are one of the most commonly used types of
clutches used in most modern light vehicles. As the name states it has
only one clutch plate. The clutch plate is simply thin metallic disc which
has both side friction surfaces.
The flywheel is attached on the engine crankshaft and rotates with it. A
pressure plate is bolted to flywheel through clutch spring, which provides
the axial force to keep the clutch engaged position, and is free to slide
on the clutch shaft when the clutch pedal is operated.

Multiplate Clutch
The multi-plate clutch is shown in the figure. These types of clutches use
multiple clutches to make frictional contact with a flywheel of the engine.
This makes power transmit between the engine. The number of clutches
means more friction surface.
The increased number of friction surfaces also increases the capacity of
the clutch to transmit torque. The clutch plates are fitted to the engine
shaft and gearbox shaft. They are pressed by coil springs and
assembled in a drum. Each of the alternate plates slides in grooves on
the flywheel and the other slides on splines on the pressure plate.
Hence, each different plate has an inner and outer spline.
The working principle of multiple clutches is the same as the working of
the single-plate clutch. The clutch is operated by pressing the clutch
pedal. The multiple clutches are used in heavy commercial vehicles,
racing cars, and motorcycles for transmitting high torque.
The multiple clutches have two characters dry and wet. If the clutch is
operated in an oil bath, it is known as a wet clutch. If the clutch is
operated dry without oil, it is known as a dry clutch. The wet clutches are
commonly used in connection with, or as a part of the automatic
transmission.
 Cone Clutch
The figure shows the diagram of a cone clutch. It consists of friction
surfaces in the form of cones. This clutch uses two conical surfaces to
transmit torque by friction. The engine shaft consists of a female cone
and a male cone. The male cone is mounted on the splined clutch shaft
to slide on it. It has a friction surface on the conical portion.
Due to the force of spring when the clutch is engaged the friction
surfaces of the male cone are in contact with the female cone. When the
clutch pedal is pressed, the male cone slides towards the spring force
and the clutch is disengaged.
Centrifugal Clutch
The below figure shows a centrifugal clutch. To keep the clutches in the
engaged position centrifugal clutch uses centrifugal force, instead of
spring force. In these types of clutches, the clutch is operated
automatically depending upon the engine speed. That’s why no clutch
pedal is required to operate the clutch.

Working of Centrifugal clutch

It consists of weights A pivoted at B. When the engine speed increases
the weights fly off due to the centrifugal force, operating the bell crank
levels, which press the plate C. The movement of plate C presses the
spring E, which ultimately presses the clutch plate D on the flywheel
against the spring G. This makes the clutch engaged. The spring G
keeps the clutch disengaged at low speeds at about 500rpm. The stop H
limits the movement of the weights due to the centrifugal.
Semi-Centrifugal Clutch
The semi-centrifugal clutch uses centrifugal force as well as spring force
for keeping it in the engaged position. The figure shows a
semi-centrifugal clutch. It consists of levers, clutch springs, pressure
plate, Friction lining, flywheel and clutch plate.
Construction of semi-centrifugal clutch:
A semi-centrifugal clutch has levers and clutch springs which are
arranged equally on the pressure plate. The springs of the clutch are
designed to transmit the torque at normal engine speed. While the
centrifugal force helps in torque transmission at higher engine speed. At
normal engine speeds, when the power transmission is low, the springs
keep the clutch engaged, the weighted levers do not have any pressure
on the pressure plate. At high engine speed when the power
transmission is high, the weights fly off and the levers also exert
pressure on the plate, keeping the clutch firmly engaged. These types of
clutches consist of less stiff springs, so that the driver may not get any
strain while operating the clutch. When vehicle speed decreases the
weights fall and the lever does not apply any pressure on the pressure
plate. Only the spring pressure is applied to the pressure plate which is
enough to keep the clutch engaged. An adjusting screw is fitted at the
end of the lever, by means of which the centrifugal force on the pressure
plate can be adjusted.

Conical spring clutch or Diaphragm clutch

The diaphragm clutch consists of a diaphragm on conical spring which
produces pressure on the pressure plate for engaging the clutch. The
spring may be finger or crown type attached on the pressure plate.
Tapered finger type spring is shown in the figure. In these types of
clutches, the engine power is transmitted from crankshaft to flywheel.
The flywheel has friction lining and it is connected to the clutch as shown
in the figure. The pressure plate is provided behind the clutch plate
because the pressure plate applies the pressure on the clutch plate. In
diaphragm clutch, the diaphragm is a conical shape of the spring. When
we press the clutch pedal the outside bearing moves towards the
flywheel pressing the diaphragm spring which pushes the pressure plate
backwards. By doing this the pressure on plate removes and the clutch
will get disengaged. When we release pressure on clutch peddle the
pressure plate and diaphragm spring will come back to its normal
position and clutch will get engaged.

Dog and spline clutch

A dog is a type of clutch it is used to lock two shafts together or to
connect a gear and a shaft. The two parts of the clutch are one is dog
clutch which has external teeth and another one is a sliding sleeve which
has internal teeth.
Both shafts are designed in such a way that one will rotate another one
at the same speed and will never slip. When the two shafts are
connected then you can say the clutch is engaged. To disengage the
clutch, the sliding sleeve moves back on the splined shaft to have no
contact with the driving shaft. The dog and splined clutch are mostly
used in manual transmission vehicles to lock different gears.

Electromagnetic Clutch
These types of clutches are operated by electrically but the torque is
transmitted mechanically. This is why this type of clutch is known as
electro-mechanical clutches. Over the year, now it became an
electromagnetic clutch. These clutches have no mechanical linkage to
control their engagement that’s why it provides fast and smooth
operation. The electromagnetic clutches are most suitable for a remote
operation that means you can operate the clutch at distance.
The clutch has flywheel consists of winding. The electricity is supplied by
the battery. When the electricity passes through winding it produces the
electromagnetic field which causes it to attract the pressure plate to get
engaged. When the electricity supply is cut off the clutch is disengaged.
In this clutch system, the gear lever has a clutch release switch that
means when the driver operates the gear lever to change gears the
switch is operated cutting off the current supply to the winding which
causes the clutch to disengage.
Vacuum clutch
The figure shows the vacuum clutch mechanism. This type of clutches
uses the existing vacuum in the engine manifold to operate the clutch.
The vacuum clutch consists of a reservoir, non-return valve, vacuum
cylinder with piston, and solenoid valve.
Construction and working:
As the figure shows the reservoir is connected to the inlet manifold
through a non-return valve. A vacuum cylinder is connected to a
reservoir through a solenoid-operated valve. The solenoid is operated
from the battery and the circuit has a switch which is attached on the
gear lever. The switch is operated when the driver changes the gear by
holding the gear lever.
When the throttle is opened the pressure increases in the inlet manifold
due to this the valve of the non-return valve closes. It separates the
reservoir and manifold thus the vacuum exists all the time in the
reservoir.
In the normal operation, the solenoid valve rod is in the bottom position
of the valve as shown in the figure and the switch in the gear lever
remains open. At this stage, the atmospheric pressure acts on both the
side of the piston of the vacuum cylinder, because the vacuum cylinder
is open to the atmosphere through the vent.
When the driver changes the gear by holding gear lever the switch gets
closed. The solenoid energizes and pulls the valve up this connects one
side of the vacuum cylinder to the reservoir. This action opens the
passage between the vacuum cylinder and the reservoir. Due to the
difference in the pressure, the vacuum cylinder piston moves forward
and backwards.
This piston movement is transferred by a linkage to the clutch, causing it
to disengage. When the driver is not operating the gear lever, the switch
is open the clutch remains engaged due to the force of springs.
Hydraulic clutch
The hydraulic clutch working operation is the same as the vacuum
clutch. The major difference between these two is that the hydraulic
clutch is operated by oil pressure whereas the vacuum clutch is operated
by vacuum.
The figure shows the mechanism of a hydraulic clutch. It has fewer parts
than other clutches. It consists of an accumulator, control valve, cylinder
with piston, pump and a reservoir.
Working of hydraulic clutch:
The oil reservoir pumps the oil into the accumulator through a pump. The
pump is operated by the engine itself. The accumulator is connected to
the cylinder through the control valve. The controlled valve is controlled
by a switch that is attached to the gear lever. The piston is connected to
the clutch by a linkage mechanism.
When the driver holds the gear lever to change the gears, the switch
opens the control valve allows the oil under pressure to the cylinder. Due
to the oil pressure, the piston moves forward and backwards this causes
the clutch to get disengaged.
When the driver leaves the gear lever the switch is open which closes
the control valve and the clutch will be engaged.
Freewheel Unit
The freewheeling unit clutches also known as spring clutch, overrunning
clutch, or one-way clutch. It is the most important part of every overdrive.
The transmission of power is in one direction similar to bicycles. The
freewheeling unit is often mounted behind the gearbox.
The power is transmitted from the main shaft to the output shaft from
driving the output shaft when the planetary gears are in overdrive. A
flywheel unit has a hub and an outer race. The hub has internal splines
to connect it to the transmission main shaft.
The outer surface of the hub contains 12 cams so designed to hold 12
rollers in a cage between them and the outer race. The outer race is
splined to the overdrive outer shaft.
Working:
When the hub is driven in the clockwise direction, as shown in the figure.
The roller rides up the cams, and by their wedging action, they force the
outer race to follow the hub. Thus, the outer race moves in the same
direction and at the same speed as the hub.
When the hub speed slows down, and the outer race is still moving
faster than the hub, the rollers move down the cams, releasing the outer
race from the hub. Thus, the outer race moves independent of the hub
and the unit acts as a roller bearing.
The transmission main shaft is connected to the hub and the output shaft
is connected to the outer race. Thus, freewheel unit can transmit power
only from the main shaft to the output shaft.

Gearbox
The gearbox is a mechanical device used to increase the output torque
or to change the speed (RPM) of an automobile. The shaft from engine
is connected to one end of the gearbox and through the internal
configuration of gears of a gearbox, provides a given output torque and
speed determined by the gear ratio.

The most basic definition of a gearbox is that it is a contained gear train,

or a mechanical unit or component consisting of a series of integrated
gears within a housing. In fact, the name itself defines what it is box
containing gears. In the most basic sense, a gearbox functions like any
system of gears; it alters torque and speed between an engine and
transmission.

Types of Gearboxes
1.Sliding mesh type gearbox
2.Constant-mesh type gearbox
 3.Synchromesh gearbox
4.Epicyclic gearbox

Sliding Mesh Type Gearbox

It is the simplest type of gearbox. The arrangement of gears is in a
neutral position. The gear housing and bearing are not shown. The
clutch gear is fixed to the clutch shaft. It remains always connected to
the drive gear of the counter-shaft.
Three other gears like first speed, second speed, and reverse speed
gear are also rigidly fixed to the countershaft or also known as layshaft.
Two gears mounted on the splined main shaft can be slid by the shifter
yoke when the shift lever is operated.
The gears are connected to the corresponding gears of the countershaft.
A reverse idler gear is fixed on another shaft and remains connected to
the reverse gear of the countershaft.

Gear is Neutral
In this position of the gear, the engine power is not transmitted to the
rear axle. When the gear is in neutral the clutch gear is transmitting the
power to gear on the countershaft and the countershaft further not
transmitting line power to the main shaft. Therefore, the output of the
gearbox is disconnected with input for the gearbox.
First or Low-speed Gear
First or low-speed gear, by operating the gear shift lever, the larger gear
on the main shaft is moved along the shaft to mesh with the first gear of
the countershaft. In this, the main shaft and the clutch shaft both rotate
in the same direction. Since the smaller countershaft gear is engaged
with the larger main shaft gear, a gear reduction of approximately 3:1 is
obtained. That is, the clutch shaft turns three times for each revolution of
the main shaft. Besides gear reduction in the differential at the rear
wheels creates a higher gear ratio, about 9:1 between the wheels and
the engine crankshaft.

Fig; Power flow through gearbox when it is in first gear

Second Speed Gear

Second speed gear, by operating the gear shift lever, the larger gear of
the main shaft is disengaged from the first gear of the countershaft, and
then the smaller gear of the main shaft meshes with the second gear of
the countershaft. In the second speed gear, the main shaft and the
clutch shaft rotate in the same direction. A gear reduction of
approximately 2.5:1 is obtained. The differential gear reduction increases
this gear ratio to about 7.5:1.

Fig; Power flow through gearbox when it is in second gear

Third Speed Gear or higher gear

Third speed gear, by operating the crankshaft lever, the second gears of
the main shaft and countershaft are disengaged, and then the second
and top gear of the main shaft is forced axially against the clutch shaft
gear. The external teeth of the clutch shaft gear mesh with the internal
teeth in the second gear and top gear. The main shaft turns with the
clutch shaft and a gear ratio of 1.5:1 is obtained. The differential
reduction produces a gear ratio of about 4.5:1 between the engine
crankshaft and the wheels.
Fig; Power flow through gearbox when it is in third gear or higher gear

Reverse Gear
Reverse gear, by operating the crankshaft lever, the larger gear of the
main shaft meshes with the reverse idler gear. The reverse idler gear is
always in mesh with the countershaft reverse gear. Interposing the idler
gear between the countershaft reverse gear and the main shaft bigger
gear, the main shaft turns in the direction opposite to that of the clutch
shaft. This changes the rotation of the wheels from forward to backward
so that the vehicle backs.

Fig; Power flow through gearbox when it is in reverse gear

Constant Mesh Gearbox
In this type of gearbox, all the gears of the main shaft are in constant
mesh with the corresponding gears of the countershaft (layshaft). As the
figure shows sliding two dog clutches are provided on the main shaft.
The one sliding dog clutch is placed in between the clutch gear and the
second gear, and the other is placed in between the first gear and
reverse gear. All gears are free on the splined main shaft.

Fig; Power flow through gearbox when it is in neutral gear

​ ​
Fig; Power flow through gearbox when it is in first gear​ Fig; Power flow through gearbox when it is in second
gear
 ​ ​

Fig; Power flow through gearbox when it is in third gear​ ​ Fig; Power flow through gearbox when it is in fourth
gear

Fig; Power flow through gearbox when it is in reverse gear

Synchromesh Gearbox
Modern cars use helical gears and synchromesh devices in the
gearboxes, that synchronize the rotation of gears that are about to mesh.
This eliminates clashing of the gears and makes gear shifting easier.
This type of gearbox is similar to the constant mesh gearbox. The
synchromesh gearbox is provided with a synchromesh device by which
the two gears to be engaged are first taken into frictional contact which
adjusts their speed after which they are engaged easily.
In most vehicles, the synchromesh devices are not fitted to all the gears.
They are fitted only on the top gears. Reverse gear, and in some cases
the first gear, do not have synchromesh devices. Because they are
intended to be engaged when the vehicle is stationary.
When the gear lever is moved the synchromesh cone meets with a
similar cone on the pinion. Due to friction the rotating pinion is, made to
rotate at the same speed as the synchromesh unit. To give a positive
drive further movement of the gear lever enables the coupling to override
several springs loaded balls and the coupling engages with the dogs on
the ride of the pinion.
Since both pinion and synchromesh units are moving at the same speed,
this engagement is necessary before engaging the dog teeth so that the
cones have a chance to bring the synchronizer and pinion to the same
speed.
Epicyclic Gearbox
In an ordinary gearing, the axes of the various gears are fixed, the
motion of the gears being simply rotations about their own axes. In
epicyclic gearing, at least one gear, not only rotates about its own axis
but also rotates bodily about some other axis. These types of gearboxes
are the most widely used in automatic transmission system. In an
automatic transmission system, there is only an accelerator and brake
will be provided. So, there will not be any clutch pedal or gear lever
available on the vehicle.

Fig; Epicyclic gear

Construction of Epicyclic Gearbox:
As the figure, this gearbox type has three gears sun gear, planet gear,
and ring gear. The sun gear is mounted on the sun gear shaft. The
planet gear is mounted on the planet carrier and the ring gear is
mounted on the planet carrier shaft. The ring gear has internal gears that
are meshes with planet gear to rotate with it. In epicyclic gearbox has
arrangement of locking gear. If one gear is locked remaining two gear
will act as input and output. For example, if the sun gear is locked the
ring gear and planet gear act as input and output members. So, by
locking at least any one gear, we can get a very different speed. The
specialty of this particular epicyclic gearbox is we can achieve a wider
variety of variations in speed.

Fluid coupling Torque converter

The main elements of the fluid coupling:
1.pump wheel,
2.turbine wheel,
3.housing

Fill the casing with liquid and start turning the inlet shaft on which the
pump impeller is fixed. The impeller blades will act on the liquid particles.
They will rotate with the blades and move from the centre to the
perimeter. The impeller is made so that the accelerated particles will be
ejected from it. These particles hit the turbine and make it rotate, while
the output shaft connected to the turbine rotates as well. The particles
are slowed down and moved towards the centre of the wheel, where
they are sucked back in by the pump. The liquid runs from the impeller to
the turbine along the perimeter and from the turbine to the impeller in the
centre. In this way, the rotation is transferred from the inlet to the outlet
shaft, but a liquid rather than mechanical transmission is used.
Such transmission provides slipping, infinitely variable rotation
frequency, the possibility of stopping the outlet shaft when the inlet one
rotates, limitation of dynamic overloads, and smoothing shocks when
transmitting torque. The fluid coupling enables torque to be transmitted
without any change, except for energy loss.

Torque converter
The main elements of the torque converter:
1.pump wheel,
2.reactor wheel,
3.turbine wheel,
4.housing
A torque converter, like a gearbox, can change the torque. For this
purpose, a reactor is installed between the impeller and turbine in the
torque converter, which ensures a spiral effect that affects the
transmission characteristics. In the converter, as in the fluid coupling, the
liquid is pressurised by the impeller and flows to the turbine, causing it to
rotate. In the torque converter, the liquid flows from the turbine outlet to
the reactor, which ensures that the flow is swirled in the direction of
rotation of the pump, resulting in more torque.
How does the reactor change torque?
The liquid particles at the outlet of the pump performs a complex
movement. On one side, they move from the impeller to the turbine. On
the other side, they rotate about the axis of rotation of the wheels. It is
the second component that affects the torque.
The reactor, which is mounted at the outlet of the turbine, spins the flow
towards the rotation of the pump impeller increasing both the rotation of
the particles around the central axis and torque.
To increase the efficiency of torque converters, impeller and turbine
locking mechanisms, free-wheel clutches that can be activated
depending on the speed or speed ratio of the engine and gear, such
mechanisms are used in torque converters in automatic car
transmissions.

Automatic transmission
An automatic transmission (sometimes abbreviated to auto or AT) is a
multi-speed transmission used in internal combustion engine-based
motor vehicles that does not require any driver input to change forward
gears under normal driving conditions. It typically includes a
transmission, axle, and differential in one integrated assembly, thus
technically becoming a transaxle.
The most common type of automatic transmission is the hydraulic
automatic, which uses a planetary gearset, hydraulic controls, and a
torque converter. Other types of automatic transmissions include
continuously variable transmissions (CVT), automated manual
transmissions (AMT), and dual-clutch transmissions (DCT). An electronic
automatic transmission (EAT) may also be called an electronically
controlled transmission (ECT), or electronic automatic transaxle (EATX).
Automatic Gearbox
An automatic gearbox uses planetary (epicyclic) gearsets instead of the
manual transmission's design of gears lined up along input, output and
intermediate shafts. To change gears, the hydraulic automatic uses a
combination of internal clutches, friction bands or brake packs. These
devices are used to lock certain gears, thus setting which gear ratio is in
use at the time.
The friction bands and clutches are controlled using automatic
transmission fluid (ATF), which is pressured by a pump and then
directed to the appropriate bands/clutches to obtain the required gear
ratio. The ATF provides lubrication, corrosion prevention, and a hydraulic
medium to transmit the power required to operate the transmission.
Made from petroleum with various refinements and additives, ATF is one
of the few parts of the automatic transmission that needs routine service
as the vehicle ages.
The valve body inside the transmission is responsible for directing
hydraulic pressure to the appropriate bands and clutches. It receives
pressurized fluid from the main pump and consists of several
spring-loaded valves, check balls, and servo pistons. In older automatic
transmissions, the valves use the pump pressure and the pressure from
a centrifugal governor on the output side (as well as other inputs, such
as throttle position or the driver locking out the higher gears) to control
which ratio is selected. As the vehicle and engine change speed, the
difference between the pressure changes, causing different sets of
valves to open and close. In more recent automatic transmissions, the
valves are controlled by solenoids. These solenoids are
computer-controlled, with the gear selection decided by a dedicated
transmission control unit (TCU) or sometimes this function is integrated
into the engine control unit (ECU). Modern designs have replaced the
centrifugal governor with an electronic speed sensor that is used as an
input to the TCU or ECU. Modern transmissions also factor in the
amount of load on an engine at any given time, which is determined from
either the throttle position or the amount of intake manifold vacuum.