Towing units for tractors
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More information can be found in the following document: •
Selecting the subframe and attachment • Subframe design • Body
adaptation brackets • Tractors
General This document describes the following:
• Refitting and retrofitting of fixed fifth wheel • Selection and
design of attaching brackets, mounting plate and subframe •
Recommendations for heavy transports
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 1 (11)
Refitting a fixed fifth wheel
Towing units for tractors
Refitting a fixed fifth wheel IMPORTANT!
Always use new screws. The old ones are worn out due to the high
tightening torque.
When the tractor is delivered from the factory, the fifth wheel is
attached to the mounting plate with M16 screws, strength class
10.9. The screws are tightened to a special torque.
Refitting of the fifth wheel is done as follows:
• Fit the fifth wheel using new M16 screws with strength class 8.8
and lock nuts (1); see illustration. Unless otherwise specified,
the standard tightening torque ap- plies.
• Weld the stop lugs (2) into place; see illustration.
Fifth wheels not previously mounted must be fitted following the
manufacturer’s in- structions.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 2 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
Retrofitting a fixed fifth wheel Scania recommends using parts from
the Scania range when retrofitting a fifth wheel, a mounting plate
or attaching brackets. Contact a Scania dealer for more
information.
The installation must follow the manufacturer’s instructions and
Scania’s recom- mendations.
Choose either attaching brackets or a subframe depending on the
following:
• Semi-trailer's load on the chassis • Chassis class • Driving
conditions
Fit the fifth wheel on a mounting plate. The mounting plate
provides good attachment for the fifth wheel to the attaching
brackets or subframe.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 3 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
92
1. Attaching bracket positioned less than 40 mm above the chassis
frame 2. Attaching bracket positioned more than 40 mm above the
chassis frame 3. Crossmember
Selection and design of attaching brackets, mount- ing plate and
subframe Attaching brackets are used as standard on tractors.
Tractors can be factory-fitted with a fifth wheel using a 2-inch
trailer kingpin. Depending on the maximum permit- ted axle pressure
load, different attaching bracket thicknesses, D values and U
values are indicated.
More information on the design of attaching brackets, mounting
plates and sub- frames for heavy transports can be found under the
heading Recommendations for heavy transports.
Attaching brackets Fit the attaching brackets in the chassis frame
beam web with a riveted joint or tight- fit screw joint. The number
of screws depends on the length of the attaching brackets, but use
at least 10 x M14 tight-fit screws.
WARNING! If the attaching brackets are positioned more than 40 mm
above the chassis frame, crossmembers must be fitted between the
attaching brackets to distribute lateral forc- es from the
semi-trailer, see illustration.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 4 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
43
Pressure distribution on the attaching bracket.
Mounting plate Scania recommends selecting components from the
Scania range. Contact a Scania dealer for more information. Select
the mounting plate based on the following re- quirements:
• D-value • Vehicle configuration • Desired fifth wheel height •
Desired trailer kingpin position, i.e. the road train’s total
length and load distribu-
tion.
The mounting plate must be designed in such a way that the pressure
on the attaching bracket is distributed evenly over at least 4
support surfaces, see illustration.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 5 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
12
Example 2: Mounting plate for low fifth wheel height.
The following 2 types of mounting plates are available, see
illustrations:
• Example 1 depicts a standard mounting plate. • Example 2 depicts
a mounting plate for a vehicle requiring a particularly low
fifth
wheel height.
WARNING! To prevent damage to the chassis frame, the end surfaces
of all mounting plates must be rounded or bent as shown in example
1.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 6 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
37
2
1
Fitting a mounting plate When retrofitting a fifth wheel, Scania
recommends longer screws combined with spacing sleeves (1) in the
joint between the mounting plate and the attaching bracket or
subframe, see illustration. The sleeve prevents the screw from
loosing its clamping force.
If the screw still looses its clamping force, the mounting plate
can, as an extra safety precaution, be locked to the attaching
brackets or the subframe with 4 welded stop lugs (2), see
illustration.
Follow the supplier’s instructions regarding attachment.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 7 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
31 5
48 0
Subframe The subframe distributes the load from the fifth wheel and
strengthens the chassis frame. It also places the fifth wheel at a
higher position and thereby creates more clearance between the
semi-trailer and chassis.
The subframe dimensions depend on the following:
• Load • Driving conditions • Space required between the tractor
and the semi-trailer.
When driving in difficult conditions or with a heavy load on the
trailer kingpin, it is suitable to use a subframe with the smallest
surface moment of inertia according to the table below.
Examples of subframes for F958 type chassis frame:
The subframe must be made of steel equivalent to that of the
chassis frame and con- sist of open profiles, Z-profiles or
U-profiles, see illustration.
Profile Height x width x depth (mm)
Minimum surface moment of inertia per beam (cm4)
U 110x80x8 380 Z 110x80x80x8 380
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 8 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
Crossmembers in front of and behind fifth wheel supporting
points.
A B C 42 3
29 3
Crossmembers and side members When cornering, lateral forces from
the semi-trailer must be distributed between frame side members. If
only one frame side member is loaded by the lateral forces, it
could become deformed. Fit crossmembers on the subframe and
position them in front of and behind the fifth wheel’s attachments,
see illustration.
For heavy transports, several strong crossmembers must be fitted on
the subframe. The crossmembers must be fitted with end pieces.
Position them in front of and be- hind the fifth wheel
attachments.
Attachments in the front section of the chassis frame (A) Fit the
subframe using flexible attachments, see illustration, that allow
the following movements in relation to the chassis frame:
• Longitudinal displacement • Certain upward movement
The size of the movements depends on driving conditions and the
torsional rigidity of the subframe.
The attachments must control the sideways movement of the
subframe.
Attachments in the rear section (B) and rear end (C) of the vehicle
Fit the subframe with rigid attachments as illustrated so that they
give the necessary rigidity between the subframe and chassis
frame.
The attachments must control the sideways movement of the
subframe.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 9 (11)
Retrofitting a fixed fifth wheel
Towing units for tractors
50
Subframe location The need for the subframe to be brought forward
increases as the axle distance in- creases. Scania always
recommends a subframe that is brought forward if axle dis- tance
exceeds 4 m. It is then recommended to bring the subframe forward
and attach it to the chassis frame as close to the foremost front
axle as possible.
Maximum permitted distance between the centre of the foremost front
axle and the front edge of the subframe is 600 mm, see
illustration. Use of the foremost body ad- aptation bracket, which
is factory-fitted, ensures that the subframe is drawn suffi-
ciently far forward.
Bringing the subframe forward decreases the load on the chassis
frame and reduces the risk of frame oscillations that cause
discomfort. This raises the chassis's natural oscillation
frequency, which means that natural oscillation does not occur
until the vehicle reaches speeds higher than the normal driving
speed.
Location of the foremost attachment Place the bodywork’s foremost
attachment point as close to the foremost front axle as possible to
counteract any frame oscillations.
Maximum permitted distance between the centre of the foremost front
axle and fore- most attachment screw in the subframe is 725 mm, see
illustration. Use of the fore- most body adaptation bracket, which
is factory-fitted, ensures that the attachment is sufficiently far
forward.
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 10 (11)
Recommendations for heavy transports
Towing units for tractors
31 5
47 8
Recommendations for heavy transports Note: The fifth wheel load is
also limited by the maximum permitted bogie weight.
Attaching brackets are used as standard on tractors. Tractors can
be factory-fitted with a fifth wheel using a 3.5-inch trailer
kingpin. This results in a D value of 260 kN.
An uneven road surface affects the dynamic forces, which in turn
affects the service life of e.g. chassis installations. The
recommendations apply to road trains with a gross weight of up to
70 tonnes for even road surfaces and 150 tonnes for uneven road
surfaces.
Scania recommends the use of a subframe when the above limits are
exceeded.
For heavy-haulage tractors up to 250 tonnes, the use of attaching
brackets is permit- ted even though the limitations outlined above
are exceeded. This assumes that the following requirements are
satisfied:
• Favourable road conditions • Moderate speed • Experienced
driver
Scania Truck Bodybuilder 22:10-520 Issue 2 2021-05-07 © Scania CV
AB 2021, Sweden 11 (11)
Towing units for tractors
Selection and design of attaching brackets, mounting plate and
subframe
Attaching brackets
Mounting plate