Backbumper

The rear bumpers in this category are metal components mounted on the chassis at the rear of the vehicle. They may be metal supports or steps providing access to a van's load compartment, or rear underrun protection devices for trucks. A rear underrun protection device, often referred to in the trade as a bumper or underrun bar, is specifically designed to prevent passenger cars from sliding underneath a truck in a rear-end collision. Depending on their design, rear bumpers provide mounting points for lights, reflectors, steps or parking sensors. A bumper cover, however, is not automatically a rear underrun protection device. The latter must transfer impact forces to the chassis through approved brackets. During diagnosis and replacement, it is therefore essential to establish whether the component is a metal step, a metal bumper beam or a complete safety structure.

Always identify rear bumpers using the vehicle's chassis number. Visual comparison or selection by model name alone is never sufficient. Also check the bodywork documentation: on bodied MAN TGL, TGM and TGS or Mercedes Atego, Actros and Arocs vehicles, the rear structure may have been specified by the bodybuilder. On MAN TGE and Mercedes Sprinter models, factors affecting fitment include body length, step design and towbar configuration. For buses such as MAN Lion’s City and Mercedes Citaro, the body variant and access to maintenance points behind the bumper are also relevant.

Designs include single-piece and multi-piece assemblies, plastic covers with separate support beams, and steel or aluminium crossmembers. Compare section height, wall thickness, material grade, mounting spacing, bolt hole diameters and position relative to the rear end of the chassis. Engine variants are generally not a direct determining factor; chassis configuration and bodywork are. For underrun protection devices, approval, support structure, ground clearance and distance from the rear of the vehicle must also comply with the applicable regulations, including UN (United Nations) Regulation No. 58 where relevant. Use the dimensional limits and tolerances specified in the vehicle-specific documentation.

Typical problems include dented crossmembers following contact with loading bays, cracked mounting lugs, elongated bolt holes and corrosion between overlapping mounting surfaces. Rattling often indicates loose connections or broken brackets. A misaligned rear bumper can also result from deformed chassis ends; replacing only the visible component will not resolve this. With plastic components, damaged support beams can sometimes remain hidden behind a cover that has sprung back into shape.

1. Park the vehicle on level ground, secure it against rolling and, if a tail lift is fitted, secure it in accordance with the maintenance instructions. Support heavy bumper assemblies before removal.
2. Clean the beam, brackets and mating surfaces. Inspect weld transitions, bolt holes and section corners for cracks, corrosion and signs of movement at contact points.
3. Using a measuring rule and laser, measure the height and rearward position on both sides from fixed chassis reference points. Check diagonals and mounting spacings against the manufacturer's drawing; the bodywork edge is not a reliable reference plane.
4. Check bolt hole diameters with a vernier calliper. If in doubt, have the remaining wall thickness measured ultrasonically and any metal areas suspected of cracking assessed using a non-destructive testing method suitable for the material.
5. Test the rear lights, number plate lights and parking sensors. Check wiring harnesses for pinching, connectors for moisture and sensor brackets for twisting.

Replace buckled support sections, cracked brackets and severely corroded mounting components in accordance with the repair instructions. Do not straighten or weld an approved underrun protection device unless an explicitly authorised repair procedure permits it. Additional holes, different section materials or altered bracket lengths can compromise force transfer and approval.

Install without introducing stress, using fasteners of the specified strength class and surface finish. Apply the specified tightening torques and replace single-use locking devices. Restore corrosion protection on contact surfaces as specified. Then check that the tail lift and rear doors move freely, that there is sufficient clearance around the towbar, and that the lights and sensors operate correctly. Carry out any sensor calibration in accordance with the manufacturer's procedure and record the final dimensions.