🏷️ Basic Information

Make:

Mercedes-Benz

Model:

300D

Year:

1981

Chassis Code:

W123

👋 Introduction

Vehicle Segment:

Mid-size Luxury Sedan/Coupe/Wagon

Target Audience:

Discerning buyers prioritizing build quality, durability, and diesel efficiency over outright performance

Primary Competitors:

BMW 5 Series (e.g., E12/E28), Audi 5+5, Volvo 240/740, American luxury sedans (Cadillac DeVille, Lincoln Continental - though less direct competitors)

Drivetrain:

Rear-wheel drive

Engine Emphasis:

Torquey, durable, fuel-efficient naturally aspirated diesel engine

Build Quality:

Renowned Mercedes-Benz engineering and construction typical of the era

Interior Comfort:

Comfortable seating, logical ergonomics, and high-quality materials

📋 Manual Details

Models Covered:

All 1981 Mercedes-Benz 300D models

Engine Variants Covered:

OM617.930 (3.0L Diesel)

Transmission Types Covered:

4-speed Automatic, 5-speed Manual (if applicable to specific 1981 models)

Estimated Page Count:

Estimated 500-700 pages (typical for comprehensive workshop manuals of this era)

Manual Type:

Workshop Repair Service Manual

Language:

English

Format:

PDF Download

File Format:

PDF

Print Quality:

High-resolution, scannable from original source material

Binding Type:

N/A (Digital Download)

Paper Type:

N/A (Digital Download)

📖 Manual Coverage

Engine Systems:

Diesel injection system (Bosch VE rotary pump), cylinder head, block, pistons, crankshaft, camshaft, timing, cooling, lubrication, exhaust, starting system (starter motor, glow plugs), pre-heating system

Transmission Systems:

Automatic transmission (e.g., 722.1), manual transmission (e.g., G3/27), clutch, drive shafts, differential, axles

Brake Systems:

Hydraulic system, disc brakes (front and rear), drum brakes (rear), parking brake, brake fluid specifications, bleeding procedures

Electrical Systems:

Battery, charging system (alternator), ignition system (though diesel, includes glow plug control), lighting (headlights, taillights, interior), instrumentation, wiring diagrams, fuses, relays, starter, horn

Suspension Steering:

Front suspension (independent, double wishbone), rear suspension (independent, semi-trailing arm), shock absorbers, springs, ball joints, tie rods, steering gearbox, power steering system

Body Chassis:

Body panels, doors, hood, trunk, interior trim, glass, seals, chassis lubrication points, frame structure

HVAC Systems:

Heating, Ventilation, Air Conditioning (if equipped) - blower motor, heater core, refrigerant system (if applicable)

Fuel Systems:

Fuel tank, fuel lines, fuel filter, diesel injection pump, injectors

Maintenance Procedures:

Oil change, filter replacement (oil, fuel, air), coolant flush, transmission fluid change, brake fluid flush, differential fluid change, lubrication points, belt inspection/replacement, tire rotation

Troubleshooting Diagnostics:

Engine starting problems, performance issues, drivability concerns, electrical faults, brake system issues, cooling system leaks, transmission shifting problems

Repair Procedures:

Engine rebuild (top end, bottom end), transmission overhaul, brake caliper/wheel cylinder replacement, suspension component replacement (ball joints, tie rods), steering gear repair, electrical component replacement, body panel repair

Adjustment Procedures:

Valve lash adjustment, injection pump timing, idle speed adjustment, brake adjustment (if applicable)

Special Tool Requirements:

Identification of necessary Mercedes-Benz specialty tools for various procedures

Diagnostic Capabilities:

In-depth diagnostic trees and flowcharts for common and uncommon issues

Rebuild Procedures:

Detailed, step-by-step instructions for complete engine and transmission overhauls

Specification Accuracy:

Precise torque specifications, clearances, fluid capacities, and measurement tolerances

Wiring Diagrams:

Comprehensive and clearly labeled electrical wiring diagrams for all vehicle systems

⚙️ Engine Specifications

Engine Code:

OM617.930

Engine Type:

Inline-5 Cylinder, Naturally Aspirated Diesel

Displacement:

3.0 Liters (2998 cc)

Horsepower:

Approx. 77-83 hp @ 4000 rpm (depending on specific market tuning)

Torque:

Approx. 125-130 lb-ft @ 2400 rpm (depending on specific market tuning)

Injection System:

Bosch Inline Mechanical Fuel Injection Pump (VE Type)

Fuel Type:

Diesel Fuel

Cooling Medium:

Glycol/Water Mixture

Oil Type Specification:

API CD or higher diesel engine oil, SAE 15W-40 or 10W-30 (refer to manual for exact ambient temp recommendations)

Oil Capacity:

Approx. 6.5 Liters (with filter)

🔧 Transmission

Transmission Type:

4-speed Automatic (722.1)

Transmission Type:

5-speed Manual (G3/27)

Automatic Transmission Features:

Hydraulically controlled, torque converter, distinct 'kick-down' functionality

Automatic Transmission Fluid Type:

MB 236.1 (Dexron II compatible, check manual for precise specification)

Automatic Transmission Fluid Capacity:

Approx. 8-9 Liters (total capacity, fluid change likely 4-5 Liters)

📐 Dimensions

Wheelbase:

Approx. 2794 mm (110 in)

Length:

Approx. 4725 mm (186 in)

Width:

Approx. 1780 mm (70 in)

Height:

Approx. 1420 mm (56 in)

Curb Weight:

Approx. 1450-1550 kg (3200-3400 lbs) depending on body style and equipment

Gross Vehicle Weight Rating:

Approx. 2000-2100 kg (4400-4600 lbs)

Trunk Capacity:

Generous for its class, suitable for luggage and everyday needs

🛡️ Safety Features

Crash Test Results:

No formal crash test ratings as per modern standards from the era, but known for robust construction.

Braking System:

Four-wheel disc brakes (standard on most W123 models by 1981), power assisted.

Steering:

Recirculating ball steering, power assisted.

Body Construction:

Reinforced passenger cell, crumple zones.

Seat Belts:

Three-point inertia reel seatbelts in the front, lap belts in the rear (standard)

Headrests:

Front headrests standard.

💡 Technology Features

Audio System:

Factory-installed AM/FM radio, often with a cassette player. Upgrades common.

Speaker Configuration:

Typically 4-6 speakers, strategically placed.

Cruise Control:

Optional on many models, mechanical/vacuum actuated.

ABS:

Anti-lock Braking System was not standard and less common on 1981 models compared to later years.

Connectivity Features:

None by modern standards (no Bluetooth, USB, etc.). Analog systems only.

🔧 Maintenance

Oil Change Interval:

Typically every 7,500 miles or 12 months (or per manual recommendation based on driving conditions).

Fuel Filter Replacement:

Recommended every 15,000-20,000 miles or annually.

Air Filter Replacement:

Recommended every 15,000-20,000 miles or as needed based on inspection.

Valve Lash Adjustment:

Recommended every 20,000-30,000 miles for optimal performance and longevity.

Coolant Type:

Mercedes-Benz approved ethylene glycol coolant (e.g., MB 325.0 spec or equivalent), 50/50 mix with distilled water.

Brake Fluid Type:

DOT 3 or DOT 4 hydraulic brake fluid (ensure it meets Mercedes-Benz specifications).

Power Steering Fluid:

MB 236.3 specification power steering fluid (or compatible)

Rear Axle Fluid Type:

Hypoid gear oil API GL-4 or GL-5, SAE 80W-90 (confirm manual for specific diff type)

Common Wear Items:

Ball joints, tie rod ends, sway bar links, exhaust system components, vacuum lines, transmission mounts, engine mounts.

Diesel Specific Concerns:

Glow plug system reliability, injection pump leaks (if not maintained), occasional injector issues, potential for injector pump timing drift.

Climate Control Issues:

Older HVAC systems can develop leaks, blower motor issues, or control panel malfunctions.

Preventative Maintenance:

Regularly check and replace fuel and air filters, maintain proper cooling system health, and ensure correct engine oil is used.

📚 Vehicle History

Mercedes Benz Legacy:

Founded on engineering excellence, innovation, and luxury since the late 19th century.

W123 Introduction:

The W123 series, launched in 1975, succeeded the W114/W115 'Stroke Eight' series. Known for its durability, build quality, and introduction of advanced safety features for its time.

1981 Updates:

Minor updates likely included refinements to trim, possibly options, and continued the success of the OM617 diesel.

Production Years W123:

1975-1986

W123 Production Volume:

Over 2.7 million units worldwide across all body styles (sedan, coupe, wagon, long wheelbase).

Manufacturing Locations:

Primarily Germany, with production also occurring in other global facilities.

🏆 Awards & Recognition

W123 Reputation:

Widely recognized for its exceptional durability, reliability, and longevity, often referred to as one of Mercedes-Benz's most robustly built vehicles.

Diesel Engine Accolades:

The OM617 engine gained a reputation as a 'bulletproof' powerplant, capable of hundreds of thousands of miles with proper maintenance.

Fuel Economy:

Excellent for its class and era, typically achieving 25-35 MPG highway due to the diesel engine.