🏷️ Basic Information

Make:

Mercedes-Benz

Model:

500 SEC

Model Code:

C126

Product Name:

Mercedes 500 SEC 1984-1985 Service Repair Manual

Generation Code:

C126

Chassis Code:

C126

👋 Introduction

Segment:

Luxury Grand Tourer Coupe

Target Audience:

Owners of 1984-1985 Mercedes-Benz 500 SEC seeking comprehensive repair and maintenance information.

Competitors 1984 1985:

BMW 6 Series (E24), Jaguar XJ-S

Vehicle Highlight:

The 500 SEC represented the pinnacle of Mercedes-Benz engineering and luxury for its era, combining potent V8 power with sophisticated chassis and styling.

Manual Value Proposition:

This manual provides the detailed, factory-level technical data necessary to properly maintain, diagnose, and repair the complex systems of the W126 SEC, empowering owners and independent workshops.

📋 Manual Details

Model Years Covered:

1984, 1985

Engine Variants Covered:

M117 5.0L V8 (500 SEC)

Regions Covered:

Global (primarily North American and European specifications for these years)

Estimated Page Count:

800+

Manual Type:

Factory Service Manual / Repair Manual

Language:

English

Format:

Digital (PDF)

📖 Manual Coverage

Engine Mechanical:

Complete overhaul, diagnosis, timing, valve adjustments, lubrication system

Fuel System:

Bosch K-Jetronic fuel injection system, fuel pumps, injectors, pressure regulators, air flow meter

Ignition System:

Electronic ignition, distributor, coil, spark plugs, timing control

Cooling System:

Radiator, water pump, thermostat, hoses, fan clutch, coolant types

Exhaust System:

Catalytic converter, mufflers, exhaust manifold, oxygen sensors (if applicable for region)

Transmission Automatic:

4-speed automatic (722.3), overhaul, diagnosis, fluid changes, linkage adjustment

Drivetrain:

Driveshaft, differential, axle shafts, CV joints

Suspension Front:

Independent suspension, control arms, ball joints, bushings, sway bar, shock absorbers/struts

Suspension Rear:

Independent suspension, semi-trailing arms, bushings, sway bar, shock absorbers, self-leveling suspension (if equipped)

Steering System:

Power steering, steering gearbox, pump, hoses, steering linkage

Braking System:

Front and rear disc brakes, ABS (Anti-lock Braking System) diagnosis and repair, brake fluid, master cylinder, calipers, pads, rotors, lines

Electrical System Overview:

Wiring diagrams, fuse box layout, relays, circuit protection

Battery Charging:

Alternator, voltage regulator, battery maintenance

Lighting System:

Headlights, taillights, interior lights, bulb replacement

Instrument Panel:

Gauges, warning lights, speedometer, tachometer, fuel gauge, temperature gauge

Climate Control:

Air conditioning system, heater core, blower motor, controls, refrigerant servicing

Body Exterior:

Body panels, doors, hood, trunk, bumpers, glass, seals, trim

Body Interior:

Seats, dashboard, door panels, headliner, carpeting, trim panels

Convertible Top System:

Hydraulic system, actuators, fabric maintenance, troubleshooting (if applicable to specific SEC model variants)

Power Accessories:

Power windows, power seats, central locking, cruise control, power mirrors

Routine Maintenance:

Oil changes, filter replacements, fluid checks and top-offs, spark plug replacement, belt inspection

Diagnostic Procedures:

Troubleshooting charts, fault code interpretation (OBD I era or specific diagnostic tests)

Engine Repair:

Head gasket replacement, piston ring replacement, bearing replacement, crankshaft and camshaft service

Transmission Overhaul:

Complete disassembly and reassembly of the 722.3 automatic transmission

Brake System Repair:

Caliper rebuilds, rotor replacement, ABS component service

Suspension Component Replacement:

Bushings, ball joints, tie rods, shocks/struts, control arms

Electrical Troubleshooting:

Diagnosing circuit faults, testing relays and switches, wiring harness repair

Fuel Injection Diagnosis:

Testing K-Jetronic components, pressure adjustments, idle mixture settings

Climate Control Service:

Refrigerant recovery/recharge, leak detection, blower motor and A/C compressor replacement

Body Work Repair:

Panel alignment, rust repair guidance, trim replacement

Convertible Top Operation:

Adjustment, fluid checks, seal replacement (if applicable)

Depth Level:

Comprehensive (from basic maintenance to full engine and transmission rebuilds)

Diagnostic Scope:

Detailed diagnostic procedures for all major systems, including specific troubleshooting trees and component testing methods.

Rebuild Procedures:

Step-by-step instructions for rebuilding major components like the engine and transmission, including torque specifications and assembly sequences.

📊 Manual Specifications

File Type:

PDF

Searchable Text:

Yes

Printable:

Yes

Image Quality:

High-resolution illustrations and diagrams

Print Format Description:

N/A (Digital PDF)

Binding Type:

N/A (Digital PDF)

Paper Type:

N/A (Digital PDF)

⚙️ Engine Specifications

Engine Code:

M117 E50

Configuration:

4.973 cc (5.0 Liters) SOHC V8

Bore X Stroke:

92.0 mm x 94.5 mm

Horsepower Approximate:

230 hp (170 kW) @ 4750 rpm (DIN)

Torque Approximate:

287 lb-ft (390 Nm) @ 3000 rpm (DIN)

Fuel Delivery:

Bosch K-Jetronic CIS (Continuous Injection System)

Fuel Type:

Premium Unleaded Gasoline

Oil Capacity With Filter:

8.0 Liters (8.5 US Quarts)

Coolant Capacity:

12.5 Liters (13.2 US Quarts)

🔧 Transmission

Type:

4-speed Automatic

Transmission Model:

722.3

Transmission Fluid Type:

Mercedes-Benz Automatic Transmission Fluid (ATF) - MB 236.2 or equivalent

Transmission Fluid Capacity:

Approximately 8.0 Liters (17.6 US Pints) for a complete fill (dry fill will be less).

📐 Dimensions

Length:

4986 mm (196.3 in)

Width:

1829 mm (72.0 in)

Height:

1438 mm (56.6 in)

Wheelbase:

2850 mm (112.2 in)

Curb Weight Approximate:

1780 kg (3925 lbs)

🛡️ Safety Features

Seat Belts:

3-point inertia-reel seat belts with front pretensioners

Airbags:

Driver's airbag became standard in later W126 models, but may not be present on all early 1984/1985 examples depending on market. Manual will cover its operation if equipped.

Construction:

Reinforced passenger cell, crumple zones

ABS:

Anti-lock Braking System (ABS) standard on many models, specifically the system found in the 500 SEC.

💡 Technology Features

Radio System:

Factory fitted AM/FM stereo with cassette player, often with power antenna. Manual covers head unit and speaker servicing.

Cruise Control:

Standard or optional cruise control system, with servicing instructions included.

Early Electronic Features:

Central locking, power windows, power seats, and optional heated seats were key electronic features of the era covered by the manual.

🔧 Maintenance

Oil Change Interval Km:

10,000 km (6,000 miles) or 12 months, whichever comes first

Transmission Fluid Interval Km:

50,000 km (30,000 miles) or 24 months (check manual for specific conditions)

Spark Plug Replacement Km:

30,000 km (18,000 miles) for standard plugs; longer for platinum

Engine Oil Specification:

API SG, ACEA A2-96 or similar; SAE 15W-40 or 10W-40 recommended (refer to owner's manual for precise viscosity based on climate)

Coolant Specification:

Mercedes-Benz Coolant (e.g., G48 or equivalent) - 50/50 mix with distilled water

Brake Fluid Specification:

DOT 3 or DOT 4

Common Wear Items:

Bushings (suspension, engine mounts), fuel distributor O-rings, vacuum lines, door seals, window regulators.

Electrical Quirks:

Aging wiring harnesses, failure of certain relays, vacuum operated central locking system issues.

K Jetronic Sensitivities:

Can be sensitive to fuel quality and air leaks, requiring meticulous diagnosis of the K-Jetronic system.

📚 Vehicle History

Brand Legacy:

Mercedes-Benz, renowned for engineering excellence, durability, and luxury.

W126 Generation:

The C126 coupe (SEC) was derived from the highly successful W126 S-Class sedan, sharing its platform, engines, and much of its luxury and safety technology. The 500 SEC was the high-performance variant of the SEC line.

Production Years W126 Sec:

1981-1991

Manufacturing Location:

Sindelfingen, West Germany

🏆 Awards & Recognition

Contemporary Reviews:

Generally lauded by automotive press for its build quality, comfort, and performance, cementing its status as a premier luxury coupe.