Gas spring for MAN / Mercedes trucks and buses

Gas struts assist with opening, holding open and controlled closing of service panels, luggage compartment doors, bonnets and tailgates. Insufficient support force causes more than just operating difficulties: a panel that drops shut unexpectedly poses an immediate safety risk. Gas struts on MAN and Mercedes trucks, buses and vans must therefore be matched to the panel weight, mounting geometry and original vehicle specification.

Always identify gas struts using the vehicle’s chassis number. Visual comparison or selection based solely on the model name is never sufficient. Also check the original part number and, for bodywork applications, the bodybuilder’s specifications. For cab-related applications, for example, MAN TGS cabs M, L and LX or Mercedes Actros cabs Lang StreamSpace and Lang BigSpace may have different mountings and panel designs. The exact specification is also crucial for Sprinter tailgates and luggage compartment doors on Lion’s Coach or Tourismo coaches.

Common types are nitrogen-filled compression gas struts with hydraulic end damping; tension and lockable gas struts are separate designs and are not interchangeable. Select according to extension force in newtons, stroke length, fully extended length between mounting centres, minimum installed length and end fittings such as ball sockets or eyelets. The gas charge pressure, effective piston rod cross-sectional area and internal friction together determine the force characteristics. The increase in force during compression and the damping zone must also suit the application.

Pay attention to corrosion protection on steel cylinders, the surface quality of piston rods and wear-resistant seals. Side loads caused by incorrect fitment damage guides and sealing lips. Follow the part specifications for length tolerances, ball stud diameters and thread sizes; a fitting that almost fits can come loose or place the panel under stress.

Typical symptoms include gradual sagging, insufficient opening assistance, jerky movement and harsh impact at the end of travel. Gas loss reduces the support force, while damaged piston rods can cause hydraulic damping oil to leak. A thin lubricating film does not necessarily indicate a fault. At low ambient temperatures, gas force decreases, which means a marginal gas strut may provide insufficient support, particularly during cold starts.

1. Support the panel mechanically before checking the mountings. Inspect hinges, ball joints, retaining clips and mounting brackets for play, corrosion and deformation.
2. Check the full range of movement for fouling, misalignment and damaged piston rods. Measure mounting distances and available stroke with a tape measure or vernier calliper; ensure the gas strut does not act as a mechanical end stop unless designed to do so.
3. Compare the force marking and dimensions with the vehicle specification. If in doubt, measure the axial force using a calibrated force gauge in a suitable test rig, at the specified temperature and measurement position. Compressing the strut by hand is not a reliable way to measure force.
4. Check whether modified panel trim, accessories or repaired hinges have changed the weight or leverage. Correct these deviations before selecting a higher force rating.

Where gas struts are fitted in pairs, preferably replace both if they have been in service for the same length of time. Unequal forces can twist the panel out of alignment. Install them in the specified orientation; on many designs, the piston rod should point downwards at rest to lubricate the seal and ensure correct end damping, but the design specification always takes precedence.

Use suitable retaining hardware and check damaged ball studs separately. Never grip piston rods with pliers, and do not drill, heat or open pressurised cylinders. After installation, check several complete opening and closing cycles, the locking mechanism and whether the panel stays open safely. A stronger gas strut is not a solution for worn hinges: excessive extension force can damage mounting points and sheet metal.