Gearbox is a device that changes the speed and torque between an engine and driving wheels. It has several purposes, including allowing the engine to disconnect from driving wheels, connecting the engine and wheels smoothly without shock, and providing leverage to vary the relationship between engine and wheel speeds. There are several types of gearboxes, including manual transmissions, automatic transmissions, and epicyclical gearboxes. A sliding mesh gearbox is the simplest type - it uses spur gears and has gears on a main shaft that can slide to engage with gears on a lay shaft, changing gears. In neutral, with the engine running and clutch engaged, gears on the transmission shaft do not rotate and no motion is transmitted to the output shaft,

1. GEARBOX
Gearbox is a speed and torque changing device.
It changes speed and torque between engine and driving
wheels.
The mechanism through which the driving torque of the
engine is transmitted to the driving wheel is the gearbox.
PURPOSES/ FUNCTIONS OF GEAR BOX
It helps the engine to disconnect from driving wheels.
It helps the running engine to be connected to the driving
wheel smoothly and without shock.
It provides the leverage between engine and driving
wheels to be varied.
It helps the driving wheel to be driven at different speeds.
It gives the relative movement between engine and driving
wheels due to flexing of the road springs.
TRACTIVE EFFORT
The torque available on the wheel produces a driving force
which is parallel to the road known as “Tractive effort”.
TYPES OF GEARBOX
1. Manual transmission
i) sliding mesh gearbox

2. ii) Constant mesh gearbox
iii) Synchromesh gearbox
2. Automatic transmission
i) Hydromantic gearbox
ii) Torque converter gearbox
3. Epicyclical gearbox
SLIDING MESH GEAR BOX
Simple in construction, Simplest type of gearbox.
In this gearbox, spur gears are used.
It consist of following parts.
1. output shaft
2.Low and reverse sliding gear
3. Second sliding gear
4. clutch
5. Input shaft
6. Clutch gear
7. Counter shaft drive gear
8. Counter shaft
9.Low speed gear
10. Second gear
11. reverse gear
12. Reverse idler gear
13. Gear shift fork

3. There are three gears (1,6 and 5) attached on the main
shaft and four gears (2,3,4 and 7) are on the lay shaft.
The two gears on the main shaft (6 and 5) can be slide by
a shifting yoke and mesh with the gears (3 and 4) on lay
shaft.
Therefore it is called “sliding mesh gearbox”. A separated
idler gear (8) is mounted on the idler shaft.
GEARS IN NEUTRAL
When the engine is running and the clutch is engaged, the
counter shaft is driven by the clutch gear.
The clutch gear rotates in opposite direction to the counter
shaft.

4. The low speed and high speed gears that are fitted on the
transmission main shaft or gearbox shaft do not rotate
because they are not engaged with any driving gears.
Therefore there is no motion transmitted from clutch to
output shaft.
Hence the vehicle is stationary.
CONSTANT MESH GEARBOX
All gears are constantly mesh and dog clutches are used
for engaging and disengaging the gears.
Helical and double helical gear teeth can be used for the
gears.
This type gears having less damaging during meshing
because the gear diameter are smaller with few numbers
of teeth.
So this type has more defects when compared o
synchronous type.

5. ADVANTAGES OF CONSTANT MESH GEARBOX
OVER SLIDING MESH GEARBOX
Quicker gearing can be achieved
Only damage occurs on dog clutch teeth not teeth of gear
wheels.
Synchronizing devices can be used for smooth
engagement of gears.
Once the dog clutches are engaged there is no motion
between their teeth but the power is transmitted through
the sliding action on teeth on one wheel on those of other
when the gear teeth are engaged.

6. To transmit the motion properly, the teeth are suitably
shaped.
SYNCHROMESH GEARBOX
To simplify the operations of changing gears without the
occurrence of clashes and their consequent damage, a
synchromesh gearbox is used in different type of motor
vehicles.
Helical gears are used
It has synchromesh unit instead of dog clutch.
The synchronizer helps to synchronize the speeds of two
gears to be engaged.
ADVANTAGES
Gear changing is very much simplified
Less wear in gears
Quiet
DISADVANTAGES:
Design is very much complex
Initial cost is high
Quick change of gears occurs due to noise of crashing
TORQUE CONVERTER
Constructional features are similar to fluid flywheel.
The only difference is that it has an ordinary stationary
member called “stator or reaction member”.

7. All the members have blades or vanes of specified shape.
But the operation is not similar.
In fluid flywheel same torque is transmitted as given by the
engine shaft.
But the torque converter increases the torque in the ratio
of about 2:1 to 3:1