Conventional Coil Suspension — What to Inspect and When
Mercedes models with conventional coil spring suspension (most W205 C-Class base trims, GLC, and non-AIRMATIC versions of older models) use coil springs with conventional hydraulic shock absorbers. These components don't fail abruptly — they degrade progressively. A shock absorber that's at 70% of its original damping performance feels normal to a driver who's been in the car every day. A pre-purchase test drive or objective bounce test reveals the difference.
Suspension inspection should occur at every Service B (approximately every two years or 20,000 miles): visual inspection of shock absorber housings for fluid leaks, measurement of ride height at all four corners, inspection of control arm bushings for cracking, check of ball joint play, and steering rack boot condition check. Suspension component wear on Simi Valley roads — which include a mix of well-maintained arterials and rougher secondary roads — is moderate compared to northern California or northeast markets.
Shock and Strut Replacement Intervals
Mercedes does not publish a fixed shock/strut replacement interval. Industry consensus for European luxury vehicles in normal driving is 80,000–100,000 miles for shock absorbers. Any shock absorber that's leaking externally needs immediate replacement — a weeping seal indicates the internal hydraulic pressure has been compromised and the unit's damping performance is already degraded. Uneven tire wear pattern (typically a scalloped or cupped pattern on the tread) is a symptom of worn shocks causing wheel hop.
AIRMATIC Maintenance — Proactive Approach
AIRMATIC air suspension has a more definitive service profile than conventional suspension because its failure mode is more acute. The proactive maintenance approach for AIRMATIC-equipped vehicles:
- Annual compressor inspection: Listen for normal vs. labored cycling. A compressor that runs frequently or sounds strained is compensating for a slow strut leak. Catching the strut before the compressor fails avoids a two-part repair.
- Height sensor inspection: At every Service B, verify all four corner height sensors are reading correctly in XENTRY. A sensor reading slightly out of spec often indicates a developing problem before any symptoms are obvious.
- Air line and fitting inspection: On higher-mileage AIRMATIC vehicles (100,000+), the plastic air lines that distribute compressed air to each corner can develop micro-cracks. A slow leak from a line is harder to diagnose than a strut leak but causes the same compressor overload sequence.
- Reservoir tank inspection: The reservoir (accumulator) on most AIRMATIC systems allows the car to raise and lower without running the compressor for every small adjustment. A failed reservoir causes the compressor to run more frequently. Reservoir failures are less common than strut or compressor failures but worth inspecting on 100,000+ mile vehicles.
Steering Components
Most modern Mercedes models use electric power steering (EPS) rather than hydraulic power steering (HPS). EPS has fewer regular service requirements — no power steering fluid to inspect or change. The main service consideration for EPS is steering rack replacement if internal wear or damage develops; the electric motor and control module are generally very reliable.
Older Mercedes models with hydraulic power steering (W211, W221, W164) use Pentosin CHF-11S power steering fluid. Fluid should be inspected at each Service B for color and level. Dark or burning-smelling fluid indicates pump seal deterioration. Power steering leaks on older Mercedes are commonly from the high-pressure hose connections at the rack or pump — inspection is visual and straightforward.
Alignment After Suspension Work
Any suspension component replacement on a Mercedes — shock absorbers, control arms, ball joints, or struts — requires a four-wheel alignment afterward. Mercedes has specific alignment specifications that are tighter than most vehicles; factory-specified toe settings in particular are precise and directly affect tire wear and stability system calibration. An alignment performed without Mercedes factory specs as the target is not a correct alignment for these vehicles.