1955–1980 Mercedes Benz Unimog 404.0 & 404.1 Service and Repair Manual

This Ars Technica Electrographics collection brings together operation, service, repair, and parts information for the Mercedes Benz Unimog Type 404.0 and 404.1 (1955-1980).

The 914-page PDF contains eight sections, with English workshop material, a German front-winch booklet, and supplementary technical illustrations.

• Engine repair: M180 disassembly and reassembly, cylinder-head and crankshaft work, plus M130 reconditioning specifications and engine-specific adjustment data.

• Fuel and cooling: Zenith carburetor overhaul and synchronization, fuel-pump testing, coolant-pump service, thermostat inspection, and cooling-system leak checks.

• Transmission and axles: UG1/11 rebuilding, supplementary crawler gear and PTO service, differential setup, and front and rear portal hub-drive repair.

• Brakes and steering: Hydraulic brake bleeding, compressed-air brake assistance diagnostics, trailer-control valve repair, and recirculating-ball steering overhaul.

• Electrical systems: Model-specific wiring diagrams, starting and charging tests, ignition troubleshooting, and supplementary radio and emergency-vehicle circuits.

• Cab and winch: Open- and closed-cab removal, tilting-cab procedures, and Type C front cable winch disassembly and reassembly.

The internal overhaul work suits experienced mechanics equipped with precision measuring instruments and the pullers, measuring fixtures, and assembly tools specified in the procedures.

M180 Engine Repair and M130 Reconditioning Data

Internal engine work covers cylinder-head repair, valve guides and seats, crankshaft bearings, piston rings, camshaft alignment, and timing-chain replacement. Early and later valve-clearance arrangements receive separate instructions; the M130 tables provide machining tolerances, wear limits, and repair-stage dimensions.

Engine lubrication coverage includes oil-pump installation and oil-pressure relief-valve specifications. The appended M180.952/.953/.958 and M130.922/.925 sections contain illustrated parts lists. OM615 diesel engine overhaul is outside the repair coverage.

Zenith Carburetors, Fuel Delivery, and Cooling

M180 carburetor adjustment and M130 dual-Zenith synchronization are treated separately. Fault charts connect poor idle, flooding, high fuel consumption, and hesitation with possible causes. The accompanying ignition and compression checks help narrow down rough-running faults before committing to carburetor repair.

Fuel-delivery procedures cover diaphragm and plunger pumps, including pressure and vacuum testing. Exhaust-manifold heating-flap checks, water-pump sealing, thermostat testing, radiator cleaning, and cooling-system modifications are also included.

The carburetor reassembly notes explain how overtightening the idle-mixture screws damages their tapered tips.

UG1/11 Transmission and Portal Axles

The fully synchronized gearbox section covers the synchromesh sliding collar, main shaft, countershaft, shifting plate, and PTO drive shaft. Axle procedures address the front differential, rear hub reduction, steering-knuckle bearings, and portal axle housings.

Spiral-bevel gear contact-pattern charts accompany the differential adjustments. Wheel-hub repair includes bearing-endplay measurement and selection of compensating rings. Special-tool references include axle-drive measuring device 401 589 00 23 00.

A separate, independently written guide documents the UG1/11 conversion from six to eight forward speeds, with shift-pattern and power-flow diagrams. The illustrated conversion uses the original PTO control position and prevents operation of the original UG1/11 PTO while driving.

Hydraulic Brakes, Air Assistance, and Steering

Single- and dual-circuit hydraulic systems, compressed-air assistance, vacuum boosters, and trailer-brake controls have separate diagrams and service instructions. Coverage includes hydraulic bleeding, booster seals and valves, air-compressor overhaul, pressure regulators, and parking-brake adjustment.

Brake-booster reconditioning is limited to the permitted rubber components and valves; damage to the piston, running surface, or piston rod calls for replacement of the unit. Steering coverage includes diagnostic worksheets, the L 3.5 K exploded view, and mechanical recirculating-ball steering adjustment and overhaul.

Always depressurize the compressed-air system before servicing brake components and ensure the vehicle is securely chocked and supported on heavy-duty stands during axle or transmission maintenance.

Wiring Diagrams and Electrical Repair

Electrical references include the 404.0 wiring diagram and the 404.114 Indonesia 12-volt diagram, alongside special-vehicle and 24-volt radio-equipment circuits. Component keys accompany the schematics, with starter, DC generator, alternator, and regulator service information.

The alternator precautions explain how disconnecting battery or charging connections with the engine running can destroy the rectifier diodes.

Front Winch and Parts Identification

The English workshop section covers Type C front-winch overhaul. The German installation and operating booklet distinguishes Type A winches with a reversing ratchet from Type C winches with reduction gearing and a band brake.

Chassis and engine exploded views accompany part-number tables with variant columns and chassis, axle, transmission, and engine-number footnotes. Lubrication-point charts, fluid capacities, and component torque tables provide additional service references.

PDF Sections, Search, and Navigation

The following counts total 914 pages. All covers, dividers, reference sheets, and blank pages within these sections are already included.

Text search works in parts of the collection, particularly the transmission modification guide and many parts tables; most operating and workshop pages and wiring diagrams are not searchable. Embedded bookmarks navigate the main sections, although the OM617A bookmark has no destination. Small wiring-diagram labels require magnification.