Dwarsbalk

Crossmembers connect the chassis side members, maintain the correct spacing between them and contribute to the designed bending and torsional stiffness. Depending on their position, they also support drivetrain components, suspension parts or a rear coupling device. A damaged crossmember therefore affects more than just frame geometry: loose connections can cause knocking noises, shifting mounting points and fatigue cracks in adjacent chassis components.

Types include open U-sections, pressed crossmembers and closed box sections, with bolted, riveted or welded connections. Structural steel and high-strength steel are used according to the required load capacity and design. Section height, wall thickness, material strength, connection radius and hole pattern together determine the mechanical properties. A heavier-duty version is not automatically suitable: excessive local stiffening can transfer stresses to the chassis side members.

For MAN TGL, TGS and TGX or Mercedes Atego, Actros and Arocs, for example, versions depend on wheelbase, axle configuration, chassis width and bodywork. For buses and vans such as Citaro, Sprinter and TGE, a distinction must also be made between separate chassis designs and integrated load-bearing structures. Engine and gearbox variants are relevant when the crossmember also carries drivetrain mounts; the mounting height and clearance must then match.

Always identify parts using the vehicle's chassis number, together with the mounting position and any documented bodywork modifications. Visual comparison or selection based solely on the model name is never sufficient. Also check part numbers, mounting brackets, drilled holes and specified fasteners.

The crossmember at the rear of the chassis on which the trailer coupling is mounted must comply with the applicable type-approval requirements of UN/ECE Regulation No. 55 (R55). This regulation sets requirements for mechanical coupling devices and their components, including strength, testing, marking and installation. When selecting a crossmember, check the type-approval number and permissible load ratings, including the D or Dc value and, where applicable, the V and S values. These must be suitable for the vehicle and trailer combination. Approval of the trailer coupling alone is not sufficient: the rear crossmember, fasteners and installation must also conform to the approved configuration and the vehicle manufacturer's specifications.

Braem is a Traxion distributor and supplies rear crossmembers that comply with R55 legislation. Choose the appropriate version based on the chassis, coupling and required load ratings. The corresponding type-approval and installation documentation remains decisive in determining the permitted application.

Typical damage includes corrosion between overlapping connection plates, elongated bolt holes, loosening riveted joints and fatigue cracks at section transitions. On tippers, crane bodies and vehicles used intensively off-road, areas subject to alternating torsional loads require particular attention. Rust marks around bolt heads or polished contact surfaces may indicate relative movement; repeated retightening does not address the cause.

1. Take the vehicle safely out of service, chock the wheels and support the chassis at the specified points. Secure any supported assemblies separately. Lowering the air suspension alone does not relieve the stresses in the structure.
2. Clean the connections and inspect them using directed lighting, a mirror or a borescope. Remove the coating locally where cracking is suspected, without damaging the base material.
3. Measure chassis width, diagonals and height differences between specified reference points using measuring rods or a chassis laser. Compare the results with the manufacturer's dimensions and tolerances; generic millimetre limits are not reliable.
4. Assess the remaining wall thickness in corroded areas using calibrated ultrasonic thickness measurement. Have suspected cracks examined using magnetic particle testing on ferromagnetic steel or dye penetrant testing on suitable, cleaned surfaces.
5. Check bolt hole diameters, ovality and joint fit using suitable internal measuring tools. At the same time, inspect the chassis side members, angle brackets and body mountings to establish the original overload or source of movement.

Unacceptable cracks, material loss or permanent deformation require repair or replacement in accordance with the vehicle manufacturer's specifications. Do not use mounting bolts to pull a distorted chassis into alignment with the new crossmember. First restore the geometry and damaged mating surfaces. Use the specified bolt strength class, fit, tightening method and assembly sequence; replace single-use fasteners.

Welding, heat straightening, drilling additional holes or converting riveted joints to bolted connections is only permitted when the manufacturer has issued an appropriate procedure. After installation, restore the corrosion protection and check drainage, clearance around pipes and lines, and chassis geometry. Record the measurement results and carry out any follow-up checks as specified. Braem can provide technical support with part identification using the chassis number.