Positioning:
The Mercedes-Benz 500SEC W126 represented the pinnacle of luxury coupe engineering and performance in the mid-1980s, a grand tourer competing with high-end offerings from BMW and other European luxury manufacturers.
Competitors:
Primarily competed with the BMW 6 Series (e.g., 633CSi, 635CSi) and other exclusive coupes of the era.
Coupe Design:
Elegant and timeless coupe body style, designed for comfort and performance, embodying the 'Sophistication through engineering' philosophy of Mercedes-Benz.
Luxury Appointments:
High-quality interior materials, advanced (for the era) comfort features, and a focus on driver and passenger refinement.
Performance Focus:
Powerful V8 engine delivering smooth and strong acceleration, coupled with sophisticated suspension and braking for confident handling.
Value Proposition:
Provides comprehensive, factory-level repair and maintenance data, crucial for preserving the longevity and performance of a classic luxury vehicle like the 500SEC.
Engine:
Complete engine diagnosis, repair, and overhaul for the M117 V8 engine.
Fuel System:
Fuel injection system (Bosch KE-Jetronic), fuel pump, lines, injectors, pressure regulators.
Ignition System:
Ignition timing, coil, distributor, spark plugs, control modules.
Cooling System:
Radiator, fan, water pump, thermostat, hoses, coolant specifications.
Lubrication System:
Oil pump, oil filter, oil passages, oil specifications.
Exhaust System:
Manifolds, catalytic converter, mufflers, exhaust hangers, emissions components.
Transmission:
Automatic transmission (likely 4-speed 722.3 or 722.4), torque converter, valve body, fluid service, overhaul.
Drivetrain:
Driveshaft, universal joints, rear axle, differential, half-shafts.
Suspension:
Front and rear suspension components, control arms, ball joints, bushings, shock absorbers, springs, alignment procedures.
Steering:
Power steering system, steering gear, steering column, tie rods, hydraulic fluid.
Brakes:
Front and rear disc brakes, ABS (if equipped), brake fluid, master cylinder, calipers, lines, parking brake.
Electrical System:
Battery, alternator, starter, wiring diagrams, fuses, relays, lighting system, power accessories.
Climate Control:
HVAC system, blower motor, heater core, evaporator, A/C compressor, refrigerant, climate control panel.
Bodywork:
Exterior trim, body panels, doors, hood, trunk, bumpers, glass, seals.
Interior:
Seats (adjustment, repair, upholstery), dashboard, door panels, headliner, interior trim, seat belts.
Body Electronics:
Power windows, power locks, central locking system, mirrors, sunroof (if equipped), cruise control.
Maintenance:
Routine maintenance, oil changes, fluid checks and changes, filter replacements, tune-ups.
Diagnostics:
Troubleshooting guides for common and complex issues, symptom-based diagnostics.
Repair:
Step-by-step repair procedures for all major and minor mechanical and electrical components.
Overhaul:
Complete engine and transmission overhaul procedures.
Installation:
Component installation and replacement procedures.
Adjustment:
Carburetor/fuel injection adjustments, ignition timing, valve adjustments (if applicable).
Depth:
Comprehensive, covering everything from basic maintenance to complete unit rebuilding, suitable for professional technicians and advanced DIYers.
Engine Type:
V8, SOHC (Single Overhead Camshaft)
Displacement:
4973 cc (5.0 Liters)
Bore X Stroke:
96.7 mm x 85.0 mm
Horsepower Us Spec:
Approx. 230-240 hp @ 4750 rpm (SAE net)
Torque Us Spec:
Approx. 280-290 lb-ft @ 3250 rpm (SAE net)
Injection System:
Bosch KE-Jetronic (CIS-E) Electronic Fuel Injection
Fuel Type:
Unleaded Gasoline (Premium)
Coolant Type:
Mercedes-Benz Specification Coolant (e.g., G48/G40, a silicate-free OAT coolant, or suitable equivalent)
Oil Type:
SAE 15W-40 or 10W-40 (API SF or SG specification, or MB 228.1/229.1)
Oil Capacity:
Approx. 7.5 - 8.0 Liters (with filter)
System:
Catalytic Converter, Lambda Sensor (O2 sensor), secondary air injection (on some models).
Crash Test Era:
While formal NHTSA or Euro NCAP ratings as we know them today were less standardized, the W126 chassis was engineered with advanced safety features for its time, including a robust structure and crumple zones.
ABS:
Anti-lock Braking System (ABS) was available and increasingly common in this period.
Traction Control:
Traction control (ASR - Automatic Slip Regulation) became available on later W126 models, but might not be standard or widely equipped on 84-85 SEC.
Airbags:
Driver-side airbag was introduced as an option on W126 models in the mid-80s and became standard later. Passenger airbag was typically not available on this generation.
Seatbelts:
Three-point inertia-reel seatbelts for all occupants.
Structural Design:
Reinforced passenger cell, energy-absorbing steering column, side-impact protection (door beams).
Oil Change:
Every 7,500 to 15,000 miles (12,000 to 25,000 km) or annually, depending on driving conditions and oil used. Consult manual for exact intervals.
Transmission Service:
Every 30,000 to 50,000 miles (50,000 to 80,000 km) for fluid and filter change. Crucial for longevity of the 722.3/722.4 transmission.
Coolant Flush:
Every 2-4 years or specified mileage.
Spark Plugs:
Typically replaced every 30,000 miles for platinum plugs, or earlier for standard plugs. Consult manual for specific plug type and interval.
Brake Fluid:
DOT 3 or DOT 4 (Low Viscosity, typically MB Spec 331.0 or 332.0)
Power Steering Fluid:
MB Specification 236.3 hydraulic fluid (typically a Dexron-II equivalent at the time, but modern equivalents may vary; check manual).
Fuel System Leaks:
Aging fuel lines and seals can lead to leaks, particularly from the fuel distributor or accumulator on the KE-Jetronic system.
Wiring Harness Degradation:
The original wiring harnesses, especially in engine bay and under dash, can degrade due to heat and age, leading to intermittent electrical faults.
Suspension Bushings:
Rubber suspension bushings (control arms, sway bars) are common wear items and can crack or collapse, affecting ride and handling.
Automatic Transmission Clutches:
The 722.3/722.4 transmissions are robust, but wear on clutch packs and valve body issues can occur with high mileage or poor maintenance.
Climate Control Actuators:
Vacuum-operated or electric actuators for the climate control flaps can fail, leading to poor airflow or temperature control.
Headliner Sagging:
The adhesive holding the headliner fabric to its backing can fail, causing the fabric to sag over time.
Window Regulators:
Power window regulators can become weak or fail, especially the anti-pinch mechanisms.