Mercedes Benz Mercedes Benz W126 (S Class) | History, Reliability & Buying Guide

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Mercedes-Benz W126 (S-Class): A Comprehensive Guide

The Mercedes-Benz W126, produced from 1979 to 1992, represents the second generation of the S-Class, Mercedes-Benz's flagship luxury sedan. Building upon the foundation laid by its predecessor, the W116, the W126 established a new benchmark for safety, luxury, and technological innovation in the automotive world. The "S" in S-Class stands for "Sonderklasse," meaning "Special Class" in German, and the W126 truly lived up to this designation. It was available in both standard (SE/SD) and long-wheelbase (SEL/SDL) versions, and even a coupe (SEC), catering to a wide range of discerning customers.

Generations

First Generation (1979-1985): Introduced in September 1979, featuring revised styling and improved aerodynamics compared to the W116. Engine options initially included inline-six (M110) and V8 (M116/M117) gasoline engines, along with inline-five and inline-six diesel engines for specific markets. Notable changes included the introduction of Anti-lock Braking System (ABS) as an option and a driver-side airbag later in the production run.

Second Generation (1985-1992): Received a facelift in 1985, commonly referred to as the "second series" or "Gen II." Key changes included:

Revised exterior styling: Smoother bumpers, redesigned wheels, and updated side cladding.

Engine upgrades: Introduction of more powerful engines, including the 5.6-liter M117 V8.

Interior improvements: Updated trim, seat designs, and minor changes to the dashboard layout.

Reliability & Common Issues

The W126 is generally regarded as a reliable vehicle, known for its robust build quality and durable components. However, like any classic car, it's prone to certain issues, particularly with age. Regular maintenance is crucial to ensure longevity and optimal performance.

Engine Issues:

M116/M117 V8 (3.8L, 4.2L, 5.0L, 5.6L): These engines are known for their durability but can suffer from timing chain wear, particularly in higher mileage examples. Check for rattling noises on startup, a telltale sign. Valve guide wear can also lead to oil consumption and smoking. Fuel injection systems (Bosch KE-Jetronic) can be complex and require specialized knowledge for diagnosis and repair. Vacuum leaks are common due to aged rubber hoses and can cause rough running.

M103/M104 Inline-Six (2.6L, 3.0L): Generally reliable, but head gaskets are a common failure point, leading to coolant leaks and overheating. Pay close attention to coolant levels and signs of oil in the coolant or vice versa. Timing chain guides can also wear over time.

OM603 Inline-Six Diesel (3.0L, 3.5L Turbo): Durable engines, but prone to pre-chamber cracking, especially in the 3.5L turbo version (350SD/SDL). This can lead to compression loss and difficult starting. Fuel injection pump issues can also occur. Check for black smoke and excessive engine noise.

Transmission Issues:

Automatic Transmissions: The 722.3 and 722.4 automatic transmissions are generally robust but require regular fluid changes. Delayed or harsh shifting can indicate wear in the clutches or valve body. Vacuum modulator issues can also affect shift quality. Check for leaks around the transmission seals.

Suspension & Steering:

Self-Leveling Suspension (SLS): Found on some models (usually SEL), this system can be problematic. Accumulators (nitrogen-filled spheres) often fail, leading to a harsh ride and potential leaks. The hydraulic pump and valve block can also develop issues. Converting to conventional springs and dampers is a common (though non-original) solution.

Front Suspension: Ball joints, tie rod ends, and control arm bushings are wear items. Check for play in the steering and knocking noises over bumps.

Rear Suspension: Rear subframe mounts can deteriorate over time, leading to vibrations and handling issues.

Electrical Issues:

Wiring Harness: The engine wiring harness, particularly on later models (late 80s and early 90s), is prone to deterioration due to the use of biodegradable insulation. This can lead to short circuits and various electrical problems. Inspect the wiring harness carefully for cracks and crumbling insulation.

Central Locking System: Can be finicky due to vacuum leaks in the system. Listen for the vacuum pump running excessively.

Climate Control: Complex and can be expensive to repair. Check for proper operation of all functions, including the auxiliary water pump (if equipped).

Other Common Issues:

Rust: While generally well-protected, the W126 can still be susceptible to rust, particularly in areas with harsh winters. Check around the wheel wells, rocker panels, door bottoms, and trunk floor.

Interior Condition: Sun damage can cause cracks in the dashboard and deterioration of the leather upholstery.

Driving Experience

The W126 offers a smooth, comfortable, and refined driving experience. The suspension is designed to absorb bumps and provide a supple ride. The steering is precise and well-weighted, offering good feedback. The powerful engines provide ample acceleration for both city and highway driving. The cabin is quiet and luxurious, providing a relaxing environment for long journeys. However, the W126 is a large car, so it can feel somewhat cumbersome in tight spaces. Also, the older technology may feel dated compared to modern vehicles.

Pros:

Exceptional ride quality.

Solid build quality and durable construction.

Powerful and reliable engines (with proper maintenance).

Luxurious and comfortable interior.

Timeless styling.

Cons:

Large size can make it difficult to maneuver in tight spaces.

Complex electrical and mechanical systems can be expensive to repair.

Age-related issues such as rust and deteriorated wiring harnesses.

Fuel economy is not great compared to modern cars.

Dated technology (no modern infotainment or safety features).

Buying Advice

When buying a W126, it's essential to do your research and inspect the car carefully. Look for a well-maintained example with a comprehensive service history. Pay close attention to the potential problem areas mentioned above.

Years to Look For:

1986-1991 (560SEL/SEC): These models offer the most powerful engine (5.6-liter V8) and the updated styling of the second generation. They are generally considered to be the most desirable. However, be aware of the wiring harness issue on these later models.

1984-1985 (500SEL/SEC): Still good choices, offering the 5.0L V8 and before the wiring harness issues became prevalent.

Years to Potentially Avoid (or Inspect Very Carefully):

1981-1985 (380SE/SEL/SEC): These early models with the 3.8L V8 are often considered less desirable due to lower power and potential for timing chain issues (though this should have been addressed if regularly maintained).

Diesel Models (300SD/SDL/350SD/SDL): While durable, the diesel engines can be expensive to repair. The 3.5L turbo diesel is particularly prone to pre-chamber cracking.

Any Model with Significant Rust: Rust repair can be costly and time-consuming.

Key Things to Check Before Buying:

Service History: Look for evidence of regular maintenance, including oil changes, fluid changes, and tune-ups.

Engine Condition: Listen for unusual noises, check for leaks, and inspect the oil and coolant for signs of contamination. Perform a compression test if possible.

Transmission Condition: Check for smooth and consistent shifting.

Suspension Condition: Look for signs of wear, such as worn bushings and leaking shocks. If equipped with SLS, check for proper operation and leaks.

Electrical System: Test all electrical components, including lights, windows, locks, and climate control. Inspect the engine wiring harness for deterioration.

Rust: Carefully inspect the body for rust, particularly in the wheel wells, rocker panels, and door bottoms.

Interior Condition: Check for cracks in the dashboard and deterioration of the leather upholstery.

Test Drive: Take the car for a thorough test drive to assess its overall performance and identify any potential problems.

With careful research and inspection, you can find a well-maintained W126 that will provide years of reliable and enjoyable motoring. They represent a fantastic value in the classic car market, offering a blend of luxury, style, and durability that is hard to match.
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