Mercedes S500 W140 Hydraulic Suspension Accumulator Part Number Guide

If you own a Mercedes-Benz S500 from the W140 generation, you know the ride comfort is legendary. A key component of that comfort is the hydraulic suspension system, which relies on a small but critical part: the hydraulic accumulator. Over time, these accumulators lose their nitrogen pre-charge or develop internal leaks, causing a harsh ride, rear-end sag, or warning lights. Replacing the accumulator is a straightforward fix, but you need the correct part number. This guide provides the OEM and aftermarket part numbers, how to identify your accumulator, and practical advice for replacement.

Understanding the W140 S500 Hydraulic Suspension System

The W140 S500 uses a hydropneumatic suspension system developed by Mercedes. Unlike conventional springs and shocks, hydraulic fluid is pressurized by a belt-driven pump and routed through a valve block to struts at each wheel. The accumulators are spherical metal canisters that store pressurized hydraulic fluid and nitrogen gas separated by a diaphragm. They act as shock absorbers and maintain ride height. The system typically has two accumulators: one for the front axle and one for the rear. The front accumulator is more prone to failure due to heat and load. Symptoms of a bad accumulator include a bouncy ride, increased roll, clunking noises, or the suspension failing to raise correctly.

The Correct Part Number for the Mercedes S500 W140 Hydraulic Accumulator

OEM Part Number

The original Mercedes part number for the front hydraulic accumulator on the S500 W140 is 140 328 00 33. This number may have been superseded by Mercedes to 140 328 06 33 or 140 328 07 33, so always verify with your dealer using your VIN. The rear accumulator part number is 140 328 00 34.

Aftermarket Alternatives

Several reputable brands manufacture replacement accumulators that meet or exceed OEM specifications. Common aftermarket part numbers include:

• Febi Bilstein 18677 (front) and 18678 (rear)
• Meyle 100 328 0001 (front)
• SWAG 60 93 0726 (front) These are direct replacements and often cost less than the Mercedes-branded part. However, quality varies, so stick with well-known suppliers.

How to Verify Your Accumulator Part Number

Before ordering, confirm which accumulator you need. The front accumulator is mounted near the front suspension crossmember, while the rear is near the rear axle. The easiest way is to look at the part number stamped on the metal can. Wipe away dirt and grime to read the number. It will be a 10- or 11-digit number starting with “140”. Also check your vehicle’s production date, as Mercedes made subtle changes during the W140 run (1991-1998). If you have the original part, match the number exactly. If not, query your VIN with a Mercedes dealer or online parts catalog.

Replacement Considerations

Replacing the hydraulic accumulator is a DIY-friendly job if you have basic mechanical skills, but safety is critical. The system holds high hydraulic pressure even when the engine is off. To depressurize, loosen the hydraulic fluid reservoir cap and bleed the system by cycling the suspension (engine on) to relieve pressure. Some recommend using a pressure gauge to confirm zero pressure before disconnecting lines.

Tools you’ll need: a 22mm wrench for the accumulator, a 17mm line wrench, and a drain pan. The accumulator screws into the hydraulic line and is often hand-tight. Be prepared for some fluid spillage. After installation, you must bleed the system: start the engine, raise the suspension to maximum height, and cycle the valve block several times. Check fluid level and top off with Pentosin CHF 11S or the equivalent specified in your owner’s manual.

Buying Guidance: OEM vs. Aftermarket

When buying a replacement, consider the cost and expected lifespan. OEM Mercedes accumulators are made by Sachs or ZF and are pre-charged with nitrogen to specific pressures. They typically last 60,000-80,000 miles. Aftermarket accumulators may last a similar duration, but some cheaper brands have inconsistent quality. For a car you plan to keep long-term, OEM is a safe bet. For a budget repair, Febi Bilstein is a trusted aftermarket brand used by many W140 owners. Avoid no-name parts from generic sellers.

Check the manufacturing date on the accumulator; it should be recent (within a year) to ensure the nitrogen charge hasn’t leaked. Also verify that the accumulator comes with new sealing washers (copper or aluminum). Reuse old washers can cause leaks.

Final Recommendation

For a direct fit and guaranteed longevity, choose the OEM Mercedes accumulator with part number 140 328 00 33 (front) or 140 328 00 34 (rear). If you prefer an aftermarket option, Febi Bilstein 18677 for the front is a reliable, cost-effective alternative. Always verify the part number against your old accumulator or VIN before purchasing. With the correct part and careful installation, your S500 will ride like new again.