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 instructions.
Retrofitting a fixed fifth wheel
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 recommendations.
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.
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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, mounting 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 permitted 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 subframes 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 forces from the semi-trailer, see illustration.
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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 requirements:
• 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.
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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.
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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.
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
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 behind 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.
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Subframe location The need for the subframe to be brought forward increases as the axle distance increases. Scania always recommends a subframe that is brought forward if axle distance 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 adaptation bracket, which is factory-fitted, ensures that the subframe is drawn sufficiently 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 foremost attachment screw in the subframe is 725 mm, see illustration. Use of the foremost body adaptation bracket, which is factory-fitted, ensures that the attachment is sufficiently far forward.
Recommendations for heavy transports
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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 permitted even though the limitations outlined above are exceeded. This assumes that the following requirements are satisfied:
• Favourable road conditions • Moderate speed • Experienced driver
Selection and design of attaching brackets, mounting plate and subframe
Attaching brackets
Mounting plate

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Towing units for tractors