Tractor Trailer

Familiarization
A few words from the History:
In the 1920's the fifth wheel came along.
In 1920s, the semi-trailer, whose front end rests on
the rear portion of the hauling truck tractor, was
gaining in popularity in the US.
In a semi-trailer the truck tractor has a disk,
known as the fifth wheel, located on a horizontal
platform over its rear wheels; a pin located under
the front of the trailer locks into this disk, thus
attaching the trailer to the tractor and furnishing
support for the front end of the trailer.
Topics covered
• Advantages
• AL Tractors – Major Specification
• Types of Trailers
• Trailer Axle alignment
• Trailer Suspension
• 5th Wheel King Pin details
• King Pin Offset
• 5th Wheel Coupling Function
• Tractor Brake Circuit
• Trailer Brake Circuit
• Function of Relay Emergency Valve
• Inspection & Maintenance
The Rigid Vehicle
Rigid
1. commercial vehicle carries the entire
load on its back between its axles
Limitations of Rigid Vehicles

1. There is a limit on load carried as

dictated by CMVR to protect Roads &
Bridges
2. There is limit to the load body length
which restricts maneuverability & also as
dictated by CMVR
3. Operational economy is quite low when
more rigid vehicles are employed in order
to transport more load
Solution

1. All these limitations can be successfully

overcome by connecting a trailer with a
loading platform to the rigid vehicle.

C
CI

This combination is commercially is known

as an articulated vehicle
Classification

Rigid

Commercial
Vehicle

Semi

Articulated
Full
Articulated vehicles - Advantage
• Rigid truck carries load placed on it.

•Tractor (or Prime Mover) pulls the load placed on the

trailer which is more than it can carry legally; hence this
way of transportation is more profitable.

• Ton-km pl of fuel is higher.

• Operating cost per ton/passenger transported is lower.
• Maintenance cost per ton/passenger transported is
lower.
• Investment cost per ton/passenger transported is lower.
• Crew cost per ton/passenger transported is lower.
• Marginal additional overhead costs.
Articulated vehicles - Advantage
• Almost twice the payload can be transported with a
single axle semi-trailer. With multi-axle trailers, the
maximum permissible gross weight rating (Gross Train
Weight – GTW or Gross Combination Weight) is many
times more than that of a truck alone.

• Over Dimensional Consignments (ODC) can be easily

carried. Legally, you can have the tractor trailer
combination length of 18 meters. (For a rigid truck, it is
max. 12 meters.)

•Easy maneuverability – better than a rigid truck;

however, reversing of the tractor trailer demands skill.
Articulated vehicles - Advantage
• You can have passenger double decker or an articulated
bus, or even an articulated dumper in this category. For
goods application, you can attach a loading ramp, or a
self loading equipment

• Prime mover can be detached and taken away for

service attention. No additional maintenance work.

• With the improvements in the brakes and steering

systems, they are as safe as a rigid truck.

• Can have spacious driver cabins, with out

compromising the payload or load span.
The Idea has been in existence for a long time!

One of the earlier buses of Volvo of

tractor and semi-trailer combination
Can Carry huge dimensional material
Palace like cabin; no compromise on load body.
AL Tractor Major Specification
MDV
2514 3014 3516 4018

Wheel Base in mm 3023 3023 3023 3300

(119”) (119”) (119”) (130”)
Un-laden Weights (Kg)
Front Axle 2700 2750 2840 2940
Rear Axle 1600 1650 1700 1840
Total ULW 4300 4400 4540 4780
RLW (Kg)
Front Axle 6000 6000 6000 6000
Rear Axle 10200 10200 10200 10200
Total RLW 26400 30000 35200 40200
No. Axles on
Semi-trailer 1 2 2 3
AL Tractor Major Specification
NEWGEN
4026

Wheel Base in mm 3560 (140”)

Un-laden Weights (Kg)

Front Axle 3350
Rear Axle 2100
Total ULW 5450
RLW (Kg)
Front Axle 6000
Rear Axle 10200
Total RLW 40200
No. Axles on
Semi-trailer 3
AL Tractor Major Specification
Heavies
BEAVER HIPPO

Wheel Base in mm 3253 (132”) 3810 (150”)

Un-laden Weights (Kg)

Front Axle 3580 3680
Rear Axle 2180 4200
Total ULW 5750 7880
RLW (Kg)
Front Axle 6000 6000
Rear Axle 10200 19000
Total RLW 40200 49000
No. Axles on
Semi-trailer 3 3
AL Tractor Major Specification
MDV Newgen Heavies

2614 3014 3516 4018 4026 Beaver Hippo

Wheel Base (mm) 3023 3023 3023 3300 3560 3353 3810
(119”) (119”) (119”) (130”) (140”) (132”) (150”)
Unladen
Weight (Kg)
Front Axle 2700 2750 2840 2940 3350 3580 3680
Rear Axle 1600 1650 1700 1840 2100 2180 4200
Total Unladen
Weight (Kg) 4300 4400 4540 4780 5450 5760 7880

RLW (Kg)
Front Axle 6000 6000 6000 6000 6000 6000 6000
Rear Axle 10200 10200 10200 10200 10200 10200 19000
Total RLW (Kg) 26400 30000 35200 40200 40200 40200 49000
No. of axles
on semi-trailer 1 2 2 3 3 3 3

Total RLW can be increased with trailer design

Types of Trailers (Goods)
I. Draw bar Trailer
II. Semi- Trailers
1. Running gear for LPG Bullets
2. Running gear for petroleum Tankers
3. Flat bed semi-trailers
4. Container trailers with platform
5. Container trailers with out platform
6. Semi-low bed semi-trailers
7. Low-bed semi-trailers
8. Well-bed semi trailer
9. Semi-trailers with front dolly
10. Coil carriers
III. Semi- Trailers with Special Equipment
5th Wheel Location
Centerline of 5th wheel King Pin Centerline of RA

King Pin
Offset
5th Wheel
Tractor Coupling Guide Ramps
Types of Trailers (Goods)
II. Semi- Trailers
Running gear for LPG Bullet

Bullet Running Gear

Landing Gear itself is
Chassis

Front end saddle support

with KINGPIN
Types of Trailers (Goods)
II. Semi- Trailers

Flat bed semi-trailer

Semi-low bed semi-trailer

Ramp for easy loading

Types of Trailers (Goods)
II. Semi- Trailers

Low bed semi-trailer

Low bed semi-trailer

Types of Trailers (Goods)
II. Semi- Trailers

Well bed semi-trailer

Semi-trailer with front dolly

Dolly is Auxiliary axle assembly equipped with a fifth wheel

towed by a tractor and supporting the front of, and towing one
semi-trailer (Also called twins or twin trailers)
Trailer Axles Alignment

To eliminate side-tracking, excessive tyre wear and poor

vehicle vehicle control,
• The axles of trailer should be parallel to the axles of prime
mover.
• The center points of the wheel tracks and the Fifth Wheel
King Pin should lie on a straight.line.
• Lateral shift of king pin must not exceed 3 mm
Trailer Axles Alignment

Maximum permissible misalignment of trailer axles:

• Difference in longitudinal measurement (A & A’): Center of

fifth wheel king pin to the outer ends of trailer axle: 2.00 mm
• Max un-parallelism (Difference between B & B’): 2.00 mm

This can be checked by thread & bob. This can be adjusted by

the adjustable torque arm.
Trailer Suspension

Front
Spring Hangers

Rigid Torque Arm

Assembly
Adjustable Torque
Arm Assemblies
 Front

Rocker: Equalizes load of

the front & rear springs

Axle
Trailer Suspension
 Front

The Suspension bogie is placed under the

trailer long members

Trailer Suspension
 Front

The Suspension bogie is placed under the

trailer long members

Trailer Suspension
King Pin of 5th Wheel LPG Bullet

Counter plate
fixed at the front
end of trailer

Rubbing
Plate
KING PIN

King
Pin The King Pin is
fixing fixed at the front
bolt
end of the trailer
King pin Diameter
King Pin of 5th Wheel
The King Pin is forged & machined.
It is bolted to the rubbing plate.
It is the element which takes all the traction load of the tractor
when the tractor and trailer are in motion.
Counter plate
fixed at the front
end of trailer Rubbing
Plate
King Pin
fixing bolt
King Pin Off-set
The King Pin is fixed at the front end of the trailer. It
is a hinge pin on which the 5th Wheel coupling is
hinged.

The King Pin offset or the location of the 5 th Wheel

determines the distribution of weight on tractor’s front
& rear axles. Hence its location should not be
changed.
Kingpin offset more – Steering hard, excess front tyre wear
Kingpin offset less – Wheel wander & rear tyre wear

The location of the 5th Wheel may sometimes vary for the same tractor due
to number of trailer axles, length of the trailer and the type of the trailer.
King Pin Off-set
Tractor 2614 3014
No. of Rear Axles
in Tractor 1 1
Trailer Flat bed Flat bed

No. of Axles
in Trailer 1 2
No. of Dual Wheels
per Trailer Axle 2 2
Size of King Pin 50.8 mm 50.8 mm
King Pin Offset 457 mm
Length of
Combination 13675
GTW 26.4 T 30 T
King Pin Off-set
Tractor 3516 3516 3516
No. of Rear Axles
in Tractor 1 1 1
Trailer LPG bullet LPG bullet Flat bed

No. of Axles
in Trailer 2 2 2
No. of Dual Wheels
per Trailer Axle 2 2 2
Size of King Pin 50.8 mm 50.8 mm 50.8mm
King Pin Offset 381 mm 608 mm 608 mm
Length of
Combination 12416 mm 12189 mm 15333 mm
GTW 34.14 T 34.14 T 35.2 T
King Pin Off-set
Tractor 3516
No. of Rear Axles
in Tractor 1
Trailer Long Container

No. of Axles
in Trailer 2
No. of Dual Wheels
per Trailer Axle 2
Size of King Pin 50.8 mm
King Pin Offset 608 mm
Length of
Combination 15333 mm
GTW 35.2 T
King Pin Off-set
Tractor Beaver Beaver Beaver
No. of Rear Axles
in Tractor 1 1 1
Trailer 27 KL fuel tanker LPG bullet Long
container
No. of Axles
in Trailer 2 3 2
No. of Dual Wheels
per Trailer Axle 2 2 2
Size of King Pin 50.8 mm 50.8 mm 50.8 mm
King Pin Offset 381 mm 625 mm 483 mm
Length of
Combination 16147 mm 15659 mm 15918 mm
GTW 35.2 T 40.2 T 35.2 T
King Pin Off-set
Tractor Beaver Beaver
No. of Rear Axles
in Tractor 1 1
Trailer Semi low bed Well bed

No. of Axles
in Trailer 2 2
No. of Dual Wheels
per Trailer Axle 2 2
Size of King Pin 50.8 mm 50.8 mm
King Pin Offset 483 mm 483 mm
Length of
Combination 16526 mm 18000 mm
GTW 35.2 T 35.2
King Pin Off-set
Tractor Hippo Hippo Hippo
No. of Rear Axles
in Tractor 2 2 2
Trailer 50 KL Flat bed Long
fuel tanker container
No. of Axles
in Trailer 3 3 2
No. of Dual Wheels
per Trailer Axle 2 2 2
Size of King Pin 88.9 mm (3½”) 88.9 mm 50.8 mm
King Pin Offset 381 mm 381mm 381 mm
Length of
Combination 17385 mm 16586 mm 16535 mm
GTW 49 T 49 T 44 T
King Pin Off-set
Tractor Hippo Turbo Hippo Hippo
No. of Rear Axles
in Tractor 2 2 2
Trailer Semi low bed Low bed Low bed

No. of Axles
in Trailer 3 1 2
No. of Dual Wheels
per Trailer Axle 2 4 4
Size of King Pin 50.8 mm 50.8 mm 88.9 mm (3½”)
King Pin Offset 381 mm 381 mm 381 mm
Length of
Combination 17935 mm 11270 mm 19135 mm
GTW 49 T 35.2 T 44 T
King Pin Off-set
Tractor Hippo Hippo Turbo
No. of Rear Axles
in Tractor 2 2
Trailer Semi low bed Well bed

No. of Axles
in Trailer 2 3
No. of Dual Wheels
per Trailer Axle 4 2
Size of King Pin 88.9 mm (3½”) 88.9 mm
King Pin Offset 381 mm 381 mm
Length of
Combination 16200 17935 mm
GTW 44 T 49 T
King Pin Off-set
Tractor Hippo Rhino
No. of Rear Axles
in Tractor 2 2
Trailer Well bed Semi low bed
with front Dolly
No. of Axles
in Trailer (s) 2 6
No. of Dual Wheels
per Trailer Axle 4 4
Size of King Pin 88.9 mm (3½”) 88.9 mm (3½”)
King Pin Offset 381 mm 381mm & 400 mm
Length of
Combination 18235 mm 22735 mm
GTW 44 T 139 T
King Pin Off-set
Tractor
No. of Rear Axles
in Tractor
Trailer

No. of Axles
in Trailer
No. of Dual Wheels
per Trailer Axle
Size of King Pin
King Pin Offset
Length of
Combination
GTW
5th Wheel Coupling
The 5th Wheel Coupling is
mounted on the tractor to
receive the King Pin of the
trailer
This is mounted on the
tractor with appropriate
distance from the centerline
of the rear axle/axles called
king pin offset.
5th Wheel Coupling
Parts: 1

1. Turn plate: It is stiffened all

the sides and inside. This
receives the superimposed
load from the front end of
trailer and transfers it to the
tractor.
5th Wheel Coupling
Parts:
2. Jaw: This is made out of 2
steel, machined and
hardened. It receives the
kingpin.
5th Wheel Coupling
Parts:
3. Wedge: This is made out of 3
steel, machined and
hardened. It keeps the
kingpin in position by
wedging the jaw.
5th Wheel Coupling
Parts:
4. Lever: This, attached with
the handle (5) can be 4
operated to release the
kingpin to detach the trailer
from the tractor.

5
5th Wheel Coupling
Parts:
6. Pivot pin: It pivots the 5th
wheel coupling to give 7º
articulation to the latter for
giving the needed
flexibility to the tractor
trailer combination. It is
mounted on a Pivot 6
Bracket(7)

7
5th Wheel Coupling
Servicing:

The Pivot Pin is mounted on

rubber bushings and they can
be procured for replacement

A repair kit consisting of the

jaw, wedge, their pivot pins &
springs can also be procured 6
for replacement. 6

Wearing ring kit and greasing

kit are also available for
replacement.
 Locked
Position

5th Wheel Coupling FRONT

 Released
Position

5th Wheel Coupling FRONT

 The pivot bracket & turn plate combination can
give a tilt of 8º up and 8º down needed by the
tractor trailer combination for safe operation

Universal couplers 
have 3º () tilt
angle laterally also
In India, they are yet to
be introduced

5th Wheel Coupling

Function of Brake Circuit

• Synchronized application of tractor & trailer brakes

• Synchronized release of tractor & trailer brakes
• Tractor protection on separation
• Trailer protection on separation
• Hand brake
• Deceleration of tractor
Basic Dual Line Brake Circuit
For Rigid
2 Axle vehicles
Dual Line Brake Circuit - Tractors
Basic
Dual Line Brake Circuit - Tractors

With TC 2
Valve
Dual Line Brake Circuit - Tractors
Improved
Circuit
With one
Relay
Valve
Trailer Brake Circuit
5

2
4
3 7
1
10
8
6
9

1. Emergency Brake line Palm Coupling to Relay Emergency Valve

2. Service Brake line Palm Coupling to Relay Emergency Valve
3. Relay Emergency Valve
4. Limiting & Quick Release Valve.
5. Lever Type Control Valve
Trailer Brake Circuit
5

2
4
3 7
1
10
8
6
9

6. Reservoir 50 liter Capacity

7. Graduated Hand Control Valve
8. Non-return Valve
9. Spring Brake Actuators
10. Quick Release Valve
Trailer Brake Circuit
The Tractor supplies air to the reservoir of the Trailer Brake
circuit. The brakes of Tractor and Trailer are controlled from
the Tractor.

Two lines with ISO palm couplings are provided from the
Tractor to the Trailer.

The ISO palm coupling is 3 in 1, eliminating separate shut off

cock & dummy coupling. When the trailer is detached, the outlet
from ISO palm coupling is automatically seals to
facilitate the operation of tractor brakes. When the trailer is
attached and palm couplings coupled, air passage is connected.
A plastic dust shield is provided in place of the earlier dummy
coupling.
Trailer Brake Circuit
ISO Palm couplings :

1. Red colored emergency line to supply compressed air to

Trailer Reservoir;
2. Yellow colored service line to apply Trailer brakes when
Tractor Brakes are applied.

Since 1996, the ISO palm couplings are supplied on the tractors
TOGETHER WITH trailer palm couplings and hence the trailer
manufacturer need not separately procure them.

The flexible pipes of palm couplings are color coded.

Trailer Brake Circuit
Operation of Trailer Brakes:
1. Charging:
From the Auxiliary port of System Protection Valve (port 24) of
the tractor, through the red colored emergency line & the relay
emergency valve via a non-return valve, compressed air is
charged into the trailer reservoir. Simultaneously, the service
brake chambers are also charged to apply trailer service brakes
until the safe limit of 4.5 kg/cm² is reached in the trailer
reservoir. Above this pressure, the trailer service brakes are
released and trailer becomes movable.
2. Application of Service Brakes:
When the tractor brake pedal is pressed, compressed air
pressure signal is given to the Service port of the Relay
Emergency Valve. The compressed air in the trailer reservoir is
sent to the service brake chambers to apply trailer brakes.
Trailer Brake Circuit
Operation of Trailer Brakes:
3. Release of Brakes:
When the tractor brake pedal is released, the air at the service
port of Relay Emergency Valve exhausts in to the atmosphere
through the tractor relay valve. The air from the service brake
chambers of trailer exhausts in to the atmosphere through the
Relay Emergency Valve.
4. Emergency Operation:
In case of accidental de-coupling of the trailer from the tractor,
both the emergency and service lines are snapped and loss of
pressure will occur in the emergency line. The compressed air
from trailer reservoir flows to service brake chambers of trailer
to apply brakes automatically.
5. Release of emergency brakes:
Shut off cock on the trailer reservoir to be opened.
Trailer Brake Circuit
Operation of Trailer Brakes:
6. Lever type Control Valve:
This valve has two positions. This valve should be kept in “ON”
position when the trailer is in laden condition. It should be kept
in “OFF” position when the trailer is in un-laden condition to
reduce brake force on the trailer brakes.
7. Pneumatic Parking brakes:
A parking brake line is included in the trailer brake system with
inclusion of Non-return valve, Graduated Hand Control valve,
low pressure warning switch in parking brake line, quick release
valve and spring brake actuators. The Graduated Hand Control
valve is located at the rear end of the trailer.
8. Mechanical Parking brake:
This is additionally provided to meet the mandatory
requirement of CMVR
Relay Emergency Valve – Purpose

1. Speed up the application

& release of trailer brakes

2. Apply emergency brake

in the event of trailer
breaking away from
tractor.
Relay Emergency Valve - Parts
10 A - Inlet Port
S
1 - Filter
2 - Non-return Valve
11 C - Reservoir Port
3 - Emergency Piston
5 4 - Inlet Valve
7 B B - Port to Brake Actuators
A
5 - Air Chamber
1 6 - Spring
4
7 - Exhaust Valve
2 C 8 - Inlet Exhaust Valve Assy.
3 9 - Exhaust Check
S - Service Port
10 - Air Chamber
Relay Emergency Valve - Charging

Until 4.5 ksc,

the emergency
piston covers the
inlet valve and To Brake chambers
the brake
chambers are
charged
Inlet port
To Reservoir
Relay Emergency Valve -
Emergency Brakes Release
After 4.5 ksc,
the emergency
piston uncovers
the inlet valve From Brake chambers

Inlet port

To Reservoir

To atmosphere
Relay Emergency Valve -
Service Brakes Application
Service port
Receiving signal
from tractor

To Brake chambers

Inlet port

To Reservoir
Relay Emergency Valve -
Service Brakes Application
Service port
Closure of inlet
valve and
pressure build
up in brake To Brake chambers
chambers
Inlet port

To Reservoir
Relay Emergency Valve -
Service Brakes Application
Service port
Balancing

To Brake chambers

Inlet port

To Reservoir
Relay Emergency Valve -
Emergency Brake Application
Connections
from tractor
snapped
To Brake chambers
Inlet port

From Reservoir
Inspection & Maintenance (Trailer)
Every 5000 km./every trip
1. Inspect the running gear frame, rubbing plate and
the suspension brackets for cracks and repair.
2. Check all the fasteners for tightness.
3. Lubricate the rocker pin and spring ends.
4. Check brake linings for wear; change if needed;
adjust brakes.
5. Lubricate the wheel hubs and adjust the bearing
end float.
6. Grease the surface of the turn plate and rubbing
plate.
Inspection & Maintenance (Trailer)
Every 30000 km.
1. Check the condition of rubber bushes in the torque
arm assemblies and replace if necessary.
2. Check the condition of rubber bushes in the 5 th
wheel coupling and replace if necessary.
Inspection & Maintenance (Trailer)
Every 60000 km.
1. Check and if needed, replace the brake camshaft
bearings or bushes.
2. Overhaul all the valves in the brake circuit.
Trouble Shooting
Complaints pertaining to tractor such as tyre wear,
defective braking have to be studied with tractor trailer
combination together in stead of separately.

Defects of trailer connected to brakes, axle alignment

have a bearing on tractor performance.
Thank you!