1987 Mercedes Benz 300SDL Repair Manual

The 1987 Mercedes Benz 300SDL is a luxury diesel sedan featuring the OM617 turbocharged 3.0L 5-cylinder engine, 4-speed automatic transmission, advanced suspension system, and comprehensive electronic systems. This repair manual covers maintenance procedures, troubleshooting, component replacement, and service specifications for the W126 chassis platform. Below are key sections for technical data, maintenance schedules, repair procedures, and diagnostic information.

1. Vehicle Specifications 2. Maintenance Schedule 3. Engine System 4. Transmission 5. Brake System 6. Suspension & Steering 7. Electrical System 8. Fuel System 9. Cooling System 10. Troubleshooting Guide 11. Technical Data

Vehicle Specifications

Key technical data for the 1987 Mercedes Benz 300SDL W126 chassis.

Specification	Description
Engine	OM617.952 3.0L Turbo Diesel I5
Power Output	120 hp @ 4350 rpm
Torque	170 lb-ft @ 2400 rpm
Transmission	4-speed 722.3 automatic
Fuel System	Mechanical diesel injection with turbocharger
Brakes	Front disc, rear drum with ABS
Suspension	Independent front, multi-link rear
Wheelbase	116.7 inches
Curb Weight	3,650 lbs
Fuel Capacity	21.1 gallons

Maintenance Schedule

Recommended service intervals for optimal performance and longevity.

Oil Change: Every 3,000 miles or 3 months
Fuel Filter: Every 15,000 miles
Air Filter: Every 30,000 miles
Transmission Fluid: Every 30,000 miles
Coolant Flush: Every 2 years or 30,000 miles
Brake Fluid: Every 2 years
Timing Chain: Inspect every 60,000 miles

WARNING! Use only Mercedes-Benz approved fluids and filters. Improper maintenance can void warranty.

Engine System

OM617 turbo diesel engine service and repair procedures.

Oil Change Procedure: Drain plug removal, filter replacement, refill with 15W-40 diesel oil
Glow Plug Replacement: Remove electrical connectors, extract faulty plugs, install new units
Injector Service: Bleed fuel system, remove injector lines, replace injectors
Turbocharger Maintenance: Check for shaft play, inspect wastegate function
Valve Adjustment: Cold engine procedure with feeler gauges

CAUTION! Engine components operate under high pressure. Allow system to cool before servicing.

Transmission

Type: 722.3 4-speed automatic with vacuum modulator
Fluid Capacity: 7.5 quarts including torque converter
Fluid Type: Dexron II or equivalent ATF
Shift Points: 1-2: 12 mph, 2-3: 25 mph, 3-4: 45 mph
Kickdown: Vacuum-operated for full throttle downshifts
Neutral Safety Switch: Prevents starting in gear
Transmission Mount: Rubber insulated for vibration damping

Brake System

Hydraulic brake system with front disc brakes and rear drum brakes. Includes early ABS system.

Front Brakes: Ventilated discs, single piston calipers, pad replacement procedure.

Rear Brakes: Self-adjusting drums, shoe replacement, wheel cylinder service.

ABS: Teves MK II anti-lock system, wheel speed sensors, hydraulic modulator.

Bleeding Procedure: Manual bleeding sequence: RR, LR, RF, LF. Pressure bleeding recommended.

Suspension & Steering

Independent front suspension with struts, rear multi-link system with hydropneumatic self-leveling.

Front Strut Replacement: Support vehicle, remove wheel, disconnect sway bar, replace strut assembly
Ball Joint Inspection: Check for play, replace if exceeds 0.125 inch movement
Tie Rod Ends: Inspect for looseness, replace with alignment required
Rear Suspension: Hydraulic leveling system service, accumulator replacement
Steering Gear: Recirculating ball type, adjustment for play elimination

Tip: Always perform wheel alignment after suspension component replacement.

Electrical System

12-volt negative ground system with separate engine and body control modules.

Battery: Located in engine bay, 12V 65Ah minimum rating
Alternator: 65-90 amp output, voltage regulator testing procedure
Starter: Direct drive type, solenoid engagement test
Fuse Box: Main fuse panel under dashboard, additional fuses in engine compartment
Lighting System: Headlight adjustment, bulb replacement procedures
Instrument Cluster: Removal for bulb replacement, speedometer cable service

WARNING! Disconnect battery before electrical work to prevent short circuits.

Fuel System

Mechanical diesel injection with in-line injection pump and pre-chamber combustion.

Fuel Filter: Spin-on type, water separator drain procedure
Injection Pump: Bosch VE type, timing adjustment specifications
Injectors: Nozzle testing, pop pressure 1,450-1,550 psi
Fuel Lines: High pressure steel lines, replacement procedure
Tank Venting: Evaporative system for diesel vapors
Shutoff Solenoid: Electrical fuel cut-off for engine stopping

CAUTION! Diesel fuel under extreme pressure - bleed system before disconnecting lines.

Cooling System

Pressurized cooling system with thermostat, water pump, and radiator.

Radiator: Aluminum core with plastic tanks, pressure cap testing

Thermostat: 88°C opening temperature, housing replacement

Water Pump: Gear-driven from timing chain, impeller replacement

Coolant: Mercedes-Benz approved antifreeze, 50/50 mixture

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Hard starting cold	Glow plug failure	Test glow plugs and controller, replace faulty units
Black smoke	Overfueling	Check injection timing, inspect injection pump
White smoke	Injection timing	Adjust injection pump timing to specifications
Loss of power	Turbocharger issues	Check boost pressure, inspect wastegate function
Transmission slippage	Low fluid or modulator	Check fluid level, inspect vacuum modulator
Brake pull	Caliper or wheel cylinder	Inspect front calipers, check rear brake adjustment

Diagnostic Tools: Mercedes-Benz specific tools recommended for accurate diagnosis.

Service Support: Contact authorized Mercedes-Benz service centers for complex issues.