Air suspension struts replace the conventional coil spring with a pressurised rubber air bag, allowing ride height and spring rate to be adjusted electronically depending on load and road conditions. This system is standard equipment on premium saloons and estates from Mercedes-Benz, Audi, and Land Rover where maintaining a level ride under varying passenger and luggage weights is a primary design objective. When an air spring develops a leak — most commonly where the rubber bag meets its crimped metal end cap, or where the bellow material hardens and cracks with age — the result is a corner of the vehicle that sits visibly lower than the others. The compressor then runs almost continuously to compensate, creating noise and accelerating its own wear. Arnott and Bilstein both produce OE-equivalent air struts that carry the correct OE references for the specific model-year and chassis variant, ensuring the height sensor interface, valve block connector, and mounting geometry match without adaptation. Because the air spring and damper cartridge are integrated into a single assembly on most platforms, the replacement unit restores both ride height control and damping performance simultaneously. Struts are generally renewed individually unless both sides show similar mileage-related bag deterioration.
Air struts are built to platform-specific dimensions that include the air fitting size, the electrical connector for the ride-height valve, the damper rod diameter, and the top-mount interface. Two variants of the same model sold in different markets or with different trim levels may use different struts that are physically incompatible. The OE reference on this page filters to your exact make, model, year, and body variant. Cross-reference the OE number with any part number on the old strut's label before ordering, as incorrect fitment requires returning an item charged with air.
The rubber bellows on an air spring can sometimes be replaced separately if the damper cartridge is still serviceable, and some repair kits are available for specific popular models. However, reassembly requires specialist tools to re-crimp the metal end cap correctly, and a poor seal will fail quickly. For most owners, fitting a complete replacement strut assembly from a known brand like Arnott or Bilstein is more reliable and ultimately more cost-effective than attempting bellows repair, particularly on older vehicles where the rubber has been hardening for years and other failure points are likely.
OEM air struts are manufactured to exact ride-height calibration curves that the vehicle's electronic control unit expects. Quality aftermarket units from Arnott or Bilstein replicate these curves and are designed to interface correctly with the original compressor and valve block. Lower-cost generic alternatives may use thinner rubber compound for the air bag, which reduces service life particularly in cold climates, and may not match the damper-force curve, resulting in a noticeably softer or firmer ride than the original specification intended.
The most visible sign is a vehicle that sits lower on one corner than the others, particularly after being parked overnight when a slow leak has time to deflate the bag fully. An air compressor that runs for extended periods after starting the engine, or that cycles on and off repeatedly while driving, indicates the system is struggling to maintain pressure. A warning light labelled 'suspension' or 'airmatic' on the dashboard, combined with a noticeably harsher ride or audible creaking from the front or rear corner, confirms a strut inspection is overdue.
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