Target Audience:
Mercedes-Benz owners, independent repair shops, automotive enthusiasts
Key Competitors:
BMW 5 Series (E28), Audi 5000, Cadillac Sedan de Ville, Lincoln Continental
Vehicle Attributes:
Renowned for build quality, durability, comfort, and innovative engineering; the OM617 diesel engine is legendary for its longevity and fuel efficiency.
Manual Value:
Provides professional-level repair and maintenance information, enabling owners to maintain their vehicles to factory standards, increasing longevity and resale value.
Engine Mechanical:
OM617.951 diesel engine, disassembly, assembly, overhaul, timing, lubrication, cooling
Engine Management:
Fuel injection system (Bosch inline injection pump), glow plug system, engine control unit (if applicable)
Transmission:
4-speed automatic transmission (722.3), service, repair, adjustments, fluid specifications
Drivetrain:
Driveshaft, rear axle, differential, wheel bearings
Suspension:
Front and rear suspension components, springs, shock absorbers, control arms, bushings, alignment specifications
Steering:
Power steering system, steering box, tie rods, steering linkage, maintenance and repair
Brakes:
Front and rear disc brakes, brake calipers, master cylinder, brake lines, parking brake, ABS (Anti-lock Braking System) components and troubleshooting
Electrical System:
Battery, charging system (alternator), starter motor, ignition system (pre-glow), lighting, fuses, relays, wiring diagrams
Climate Control:
Air conditioning system, heater core, blower motor, controls, refrigerant service (caution advised)
Body And Chassis:
Body panels, doors, hood, trunk, interior trim, structural components, rust prevention
Body Electrical:
Power windows, power door locks, central locking, power seats, mirrors, wipers, horn
Routine Maintenance:
Oil changes, filter replacements, fluid checks and top-offs, lubrication points, tire rotation
Troubleshooting:
Diagnostic procedures, symptom-based troubleshooting, fault code interpretation (if applicable)
Repair Procedures:
Step-by-step instructions for all major mechanical and electrical components
Overhaul Procedures:
Detailed rebuild procedures for engine, transmission, and other major systems
Installation Procedures:
Guidance on installing new or replacement parts
Technical Specifications:
Torque values, clearances, fluid capacities, electrical specifications, diagnostic data
Depth Of Coverage:
Comprehensive: Covers all aspects from basic maintenance to full engine and transmission rebuilds, including detailed diagnostics and schematics.
Crash Test Data:
NHTSA ratings for this era are less standardized. Emphasis on robust chassis construction and passive safety features.
ABS:
Available on later models within this range (e.g., 1984-1985)
Airbags:
Driver airbag became standard on later W126 models (typically from 1984/1985 onwards).
Seatbelts:
3-point front and rear seatbelts, seatbelt pre-tensioners (depending on year/market).
Chassis Design:
Advanced crumple zones, reinforced safety cage.
Oil Change Interval:
Every 5,000-7,500 miles or 6-12 months (refer to manual for specific conditions and oil type).
Air Filter Replacement:
Every 15,000-20,000 miles or as needed based on operating conditions.
Fuel Filter Replacement:
Every 15,000-25,000 miles (crucial for diesel engine health).
Transmission Fluid Change:
Every 30,000-50,000 miles or as recommended by the manual. Critical for longevity of the 722.3 transmission.
Engine Oil Spec:
API CD or CE rated diesel engine oil, viscosity grade 15W-40 or 20W-50 depending on ambient temperature (refer to manual).
Coolant Spec:
Mercedes-Benz approved coolant (e.g., silicate-free, ethylene glycol-based) in a 50/50 mixture with distilled water.
Brake Fluid Spec:
DOT 3 or DOT 4 brake fluid (ensure compatibility as per manual).
Engine Mounts:
Wear and tear leading to vibration transmitted to the cabin. Replacement is common.
Vacuum System:
Leaks in the vacuum system can affect central locking, climate control, and engine idle. The manual details troubleshooting of these lines.
Biodegradable Wiring:
Some earlier Mercedes models had biodegradable insulation on wiring harnesses, leading to degradation over time. The manual provides diagrams for identification and repair.
Diesel Injector Pump:
While robust, the Bosch injection pump can require specialized service or adjustment over time. The manual covers diagnostic and adjustment procedures.
Mercedes Benz Legacy:
Mercedes-Benz has a long-standing reputation for engineering excellence, safety, and durability, particularly in its diesel-powered vehicles.
W126 Introduction:
The W126 S-Class replaced the W116 in 1979. The 300SD was a key model, offering exceptional fuel economy and reliability in the luxury segment.
Model Updates Within Range:
Minor updates occurred between 1981-1985, including potential availability of ABS and driver airbags, and minor aesthetic refinements.
Production Years:
W126: 1979-1991 (300SD variant predominantly 1979-1985 for North America).
Engine Production:
The OM617 engine family was produced from 1974 to 1986, renowned for its robust design and longevity.
