Bonnet

A bonnet protects the engine compartment against stone impact, moisture, dirt and uncontrolled airflow, while also determining access to daily inspection points. On MAN and Mercedes vans, this body component is generally a hinged panel in front of the windscreen; on trucks, buses and coaches, the term may also refer to a front flap, service hatch or engine cover. The correct version must always be identified using the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient, as hinge points, locks, grille openings, insulation, gas struts and provisions for cameras or sensors vary by specification.

Bonnets for MAN TGE and Mercedes Sprinter, Vito, V-Class, Viano, Citan, Vario and older TN models differ according to model year, wheelbase, front-end version and fitted driver assistance systems. On MAN TGL, TGM, TGS, TGX and TG3, Mercedes Atego, Axor, Actros, Antos, Arocs and Econic, and MAN and Neoplan buses, these are often front panels or specific access covers. On Citaro, Intouro, Tourismo, Lion’s City, Lion’s Coach, Cityliner and Tourliner, the mounting points and ventilation provisions are also specification-dependent.

Depending on the vehicle type, a bonnet is made from painted sheet steel, aluminium or SMC composite (Sheet Moulding Compound). Steel bonnets offer high dimensional stability, while aluminium saves weight but is more susceptible to local denting and galvanic corrosion if incorrectly fitted with steel fasteners. Composite parts are corrosion-resistant, but may delaminate internally following an impact. Always check the fit around the headlights, front grille, wings and windscreen: uniform panel gaps are essential to prevent contact damage, wind noise and leaks.

Common faults include stone chips and paint damage on the leading edge, corrosion around hemmed seams, cracks at hinge mountings, worn latch strikers and broken bonnet supports. On vans, a bonnet that does not close properly, a height difference with the front wings or a visible kink in the inner structure often indicates previous front-end damage. On heavy vehicles, broken latches, distorted service hatches and worn hinge bushes can result from vibration, incorrect opening or impact with obstacles.

First measure the panel gap on the left and right using a feeler gauge or vernier caliper and compare the bonnet height relative to the headlamp units and wings. Then check the hinge arms for play by carefully moving the bonnet up and down. Assess the gas struts for oil traces, reduced damping force and uneven opening movement. Inspect the lock mechanism, secondary safety catch and lock cable for corrosion, cable breakage or stiffness. On vehicles with electronic release or integrated front cameras, wiring harnesses, connector locks and fault codes in the ECU (Electronic Control Unit) must also be checked.

Repair is possible for superficial paint damage, minor dents in non-structural areas and small defects in plastic trim. Replace the bonnet when the inner panel is kinked, hinge points are torn out, the composite is visibly cracked or shows delamination, or when the lock can no longer be reliably aligned. An unreliable locking mechanism is a safety risk: the bonnet may spring open while driving and obstruct visibility.

First fit a new bonnet loosely on the hinges and adjust the height, longitudinal position and panel gaps before permanently securing the latch striker. Use the specified fasteners and tightening torques; excessive preload around composite or aluminium may cause cracking. After installation, check the operation of the primary and secondary latches, sealing rubbers, washer hoses, insulation mats and any camera or sensor systems. Braem can supply bonnets in colour to minimise downtime and additional paintwork.