Segment:
Full-size luxury sedan
Target Audience:
Discerning buyers valuing comfort, durability, and diesel efficiency; also owners seeking comprehensive DIY repair resources.
Competitors:
BMW 7 Series (E23), Audi 5000, Cadillac Eldorado/Seville, Lincoln Continental.
Unique Selling Proposition:
Renowned Mercedes-Benz build quality, exceptional diesel engine longevity and fuel economy, comfortable ride, robust chassis.
Design Philosophy:
Understated elegance, functional luxury, engineering excellence.
Powertrain Emphasis:
Robust and efficient turbocharged diesel engine offering exceptional torque and long-term reliability.
Engine Mechanical:
Detailed rebuild procedures for OM617.952 diesel engine, including cylinder head, block, crankshaft, pistons, connecting rods, timing components.
Engine Management:
Fuel injection system (Bosch inline injection pump), glow plug system, exhaust system.
Transmission:
4-speed automatic transmission (722.3) overhaul, operation, adjustments, and troubleshooting.
Drivetrain:
Rear axle assembly, driveshaft, CV joints, limited-slip differential (if equipped).
Suspension:
Front independent suspension (double wishbone), rear independent suspension (multi-link), springs, shock absorbers, sway bars, bushings.
Steering:
Power steering system, steering gearbox, steering linkage, steering column.
Brakes:
Front disc brakes (ventilated), rear disc brakes, hydraulic system, parking brake, ABS (if equipped - early systems).
Electrical System:
Wiring diagrams, charging system (alternator), starting system (starter), battery, lighting, instrumentation, interior electronics, power accessories.
Climate Control:
Air conditioning system diagnosis and repair, heater core, blower motor, climate controls.
Body:
Body panels, doors, windows, locks, exterior trim, bumpers, sunroof (if equipped).
Interior:
Seats, upholstery, dashboard, trim panels, safety belts.
Routine Maintenance:
Oil changes, filter replacements, fluid checks and top-offs, tire rotation, belt inspections.
Diagnostic Troubleshooting:
Systematic diagnostic procedures for common and uncommon faults across all major vehicle systems.
Repair And Rebuild:
Detailed step-by-step instructions for component removal, disassembly, inspection, repair, and reassembly.
Adjustment And Calibration:
Procedures for adjusting idle speed, injection timing, transmission detent pressure, brake adjustments, etc.
Torque Specifications:
Comprehensive list of torque values for all critical fasteners.
Wiring Diagrams:
Detailed electrical schematics for the entire vehicle.
Depth:
Factory-level detail, suitable for professional mechanics and experienced DIY enthusiasts. Covers diagnostics, component-level repair, and complete system overhauls.
Engine Type:
Inline-five cylinder, naturally aspirated diesel (though the manual specifically covers the turbocharged variant)
Displacement:
3.0 Liters (2998 cc)
Bore X Stroke:
90.9 mm x 107.9 mm
Compression Ratio:
21.0:1
Horsepower:
123 hp @ 4350 rpm (approx.)
Torque:
183 lb-ft @ 2400 rpm (approx.)
Injection System:
Bosch inline mechanical injection pump with turbocharger, intercooler.
Oil Capacity Quarts:
7.4 (with filter)
Recommended Oil Viscosity:
SAE 15W-40 or 20W-50 (depending on climate and manufacturer recommendation for diesel engines of this era)
Audio System:
Factory AM/FM cassette stereo, often with optional power antenna and upgraded speaker systems.
Display:
Analog gauges, climate control indicators, basic warning lights.
Cruise Control:
Standard on most models, vacuum or electronically controlled.
Connectivity Options:
Limited to analog communication (e.g., antenna for radio).
Power Accessories:
Power windows, power door locks, power mirrors, power antenna, power seats (optional).
Oil Change Interval Miles:
Every 3,000 - 5,000 miles (depending on driving conditions and oil quality, consult manual for precise recommendations).
Fuel Filter Replacement Miles:
Every 10,000 - 15,000 miles
Air Filter Replacement Miles:
Every 10,000 - 15,000 miles
Transmission Fluid Change Miles:
Every 30,000 - 50,000 miles (highly recommended)
Coolant Flush Miles:
Every 2-3 years or 30,000 miles
Engine Oil Type:
Diesel engine oil, API CD or CE specification (e.g., 15W-40, 20W-50).
Power Steering Fluid:
MB 236.3 (ATF Dexron II equivalent)
Brake Fluid Type:
DOT 3 or DOT 4 (consult manual for specific Mercedes approval)
Vacuum System Leaks:
Common issue affecting central locking, HVAC controls, and engine idle stability. Diagnosis and repair of vacuum lines and actuators is crucial.
Climate Control Actuators:
Failure of vacuum-operated actuators can lead to improper HVAC temperature and airflow control.
Injector Pump Seals:
Leaking seals on the Bosch injection pump can lead to fuel leaks and starting issues.
Glow Plug System:
Faulty glow plugs or relay can cause hard starting in cold weather.
Rust And Corrosion:
Areas like wheel wells, rocker panels, and door bottoms are susceptible to rust, especially in certain climates.
Mercedes Benz Legacy:
Founded on pioneering automotive engineering, luxury, and safety standards dating back to the late 19th century.
W126 Introduction:
The W126 chassis replaced the W116 and represented a significant evolution in Mercedes-Benz design, aerodynamics, and safety technology.
300Sd Turbo Placement:
The 300 SD Turbo was the flagship diesel model in the W126 lineup, known for its fuel efficiency and durability.
Manufacturing Location:
Sindelfingen, West Germany
Production Run W126:
1979-1991 (overall chassis production)
