1939 Mercedes-Benz G4 Offroader

(from DaimlerChrysler Press Release)  This car is an extremely rare one: a 1939 Mercedes-Benz G4 offroader in original condition, today owned by the Spanish royal family. The explicit restoration order placed with the Mercedes-Benz Classic Center was correspondingly unusual. The G4 was to be restored to a technically impeccable condition but was to retain its unique patina acquired in the course of its 66-year life. A first quick glance may therefore be irritating: Is this the result of three years of painstaking restoration? It is indeed, because the restorers deliberately refrained from removing the traces of use in the interior and minor blemishes in the bodywork. These traces and blemishes do, after all, testify to the G4’s history and authenticity.

The G4 owned by the Spanish royal family is one of just a few surviving units of this three-axle offroader – just three of the total of 57 units built in the 1930s are still being considered absolutely authentic. Additional units still exist yet without unambiguous proof of their originality. Before the G4 joined the royal fleet, it was used by General Franco who had been given this car as a present from Germany. During the past decades, the offroader was serviced and maintained by the Royal Guard in Madrid. The latter hold the classics in the royal fleet in high esteem. When it was decided to have the G4 restored by the Mercedes-Benz Classic Center, together with an equally extraordinary car of its day and age, a Mercedes-Benz 770, the cars were given an almost ceremonial farewell in Madrid, and an armed escort accompanied the truck convoy to the French border. The cars arrived at the Mercedes-Benz Classic Center in Fellbach near Stuttgart in September 2001. The large 770 limousine is still there, undergoing restoration. The work on the G4, completed in December 2004, is a present by Mercedes-Benz España to the Spanish royal family.

The first inspection of the G4 in the workshop of the Classic Center revealed numerous traces of use over the years but otherwise an excellent substance overall. In a first step, the soft-top was removed and the bodywork was lifted off with utmost care to gain access to the chassis. In the course of the subsequent painstaking restoration, no component however small remained untouched. All the mechanical components were disassembled, cleaned, repaired and put together again – an attention to detail that was responsible for three years of restoration work. The experts reconstructed several functions of the elaborate engineering and made them operational again. The original substance was retained wherever this was possible – another brief for the restoration work. The extent of this is illustrated by the fact that every screw, every bolt and every sleeve was scrupulously inspected, re-machined and returned to its original position whenever possible. Another example: the inner components of the exhaust system, which were still operational, were left in their original condition whereas the dilapidated exterior components underwent true-to-the-original restoration. Non-original components were replaced by components re-produced on the basis of the old blueprints.

The three axles of the offroader were completely dismantled and overhauled. The mechanical drive assemblies proved to be in an extremely good condition. And yet they are a good example for the scope of work invested. It took a 20-ton press in the Mercedes-Benz factory in Untertürkheim to loosen the rigid shafts on the rear axles. The numerous gearwheels were cleaned in a special process based on diesel fuel because the latter’s oily consistency ensured clean surfaces yet retained a protective grease film. After the completion of the work, it was not possible to fill the customary lubricants into the axle housings because they would have had corrosive effects on the bronze components in the differentials. In addition, the oil had to have a high level of shear resistance. After a lengthy search, the experts decided in favor of a special lubricant based on castor oil.

Talking about searches: to be restored to a fully operational condition, the G4 needed new tires – eight of them, to be precise, including the spares. These tires were not easy to come by, given the required dimensions, the stability to match the high vehicle weight plus the offroad tread. Quite some time passed by before the experts eventually found the right tires in America.

The G4 has four forward gears, gears two through to four being synchronized. A countershaft transmission serves as a reduction gear, making four additional crawler gears available. For operation in difficult terrain, the differentials are self-locking, an engineering feature that was far from being state of the art for offroaders at the time the G4 was built – and for quite some time to come.
 
The G4 is powered by an M24 II eight-cylinder in-line engine with a displacement of 5.4 liters – very similar to the engine which was also used in the 540 K sports car, though without a supercharger to boost performance at high speeds. The designers of the G4 decided against a supercharger because the car, weighing some 3.7 tons, has a top speed of just 67 km/h – the tires do not permit any higher speeds. It is this high weight that accounts for the G4’s somewhat limited offroad capabilities.

The aim of restoration was “an impeccable technical condition”, and this also meant roadworthiness. Hence, the scope of work also included the repair of the brakes, a dual-circuit system testifying to the high technical standard of the overall design. Not only did the mechanical components have to be overhauled, new brake lines also had to be installed, which had to be specially manufactured: copper cables in the required dimensions and strength are not available off the shelf. The same applies to the fuel lines which were equally specially manufactured. The clean, symmetrical layout of the cables in the chassis almost resembles a work of art. Incidentally, the driver is given clever assistance when braking in order to decelerate the mighty vehicle effectively. A piston operated by a vacuum cylinder additionally acts on the brake pedal via a cable mechanism. This technical feature, including a leather sleeve in the vacuum reservoir, was reconstructed. Where the fuel supply is concerned, the designers of the G4 played it safe: the car has two electric fuel pumps, plus a mechanical pump and, in case all three fail, the engine can still be supplied with gasoline from a spare gravity fuel tank.

After the restoration, the chassis with all its components very much looks as it did in the 1930s, i.e. rather austere as the paint coat of numerous parts had not been sprayed on but applied by means of a brush, resulting in corresponding surfaces. This method was therefore also used in restoration, maximum originality being the top priority at all times.

The G4 has numerous electric functions and therefore a highly complex circuitry. However, a blueprint of this circuitry was no longer available. It was reconstructed with painstaking attention to detail and a new cable harness was manufactured, which proved to be a highly complex undertaking. For instance, the G4 features a central switch which shuts off all electricity consumers, with only the electric components required for engine operation still being supplied. Every single switch on the G4 was dismounted and repaired, at times with the most delicate tools which are reminiscent of a dentist rather than an automotive expert. Even the pale blue illumination of the Virgin Mary badge attached to the cockpit is in working order again, thanks to specially modified miniature light bulbs. All gauges were overhauled, and the precision of the electric clock was monitored and adjusted over the course of many weeks. Today, it indicates the time almost as precisely as a modern quartz clock. The orange-colored plastic in the direction indicators was beyond repair and had to be replaced. After intensive treatment, the tubular radio plays again as it did before. And when required, attention is drawn to the car by four horns - two for city traffic and two louder ones for overland trips – or a siren.

The bodywork remained largely untouched – the brief had been to refrain from cosmetic restoration. The specialists cleaned the paint coat and polished the chrome parts, but that was largely the extent of it. Only the lower sections of the doors showed signs of rust which was removed as a matter of course. The bodywork’s sheet metal is lined on the inside with stabilizing wooden elements, a customary construction for cars at the time. These wooden elements were in good condition and were therefore merely cleaned and impregnated with a special fluid to protect them from drying out.
The interior reveals traces of the car’s age of more than 65 years but is otherwise in almost impeccable condition – not least thanks to the care lavished on the car by the Royal Guard. Gentle restoration work will, if at all, be carried out in Spain where people have plenty of experience in the repair of valuable horse-drawn carriages, for instance – an expertise from which the G4 will be able to benefit.

After the restoration of the royal G4’s chassis, the car was taken to the test track on the premises of the Mercedes-Benz plant in Untertürkheim for trial driving to check on the perfect functioning of all components. After the tests, the finishing touches were added to the engineering and the last adjustments were made. Then came the great moment: the bodywork was mounted back to the chassis, repeating the act of “wedding”, as this is known in automotive lingo, and the G4 came back into being, 66 years after its first completion in 1939.

And now, the fleet of the Spanish royal family includes a truly unique vehicle, the extremely rare Mercedes-Benz G4 offroader, fully operational with completely overhauled mechanical components but with all the deliberately retained traces of its venerable age. It is thus a very special witness to contemporary and engineering history.

General information: Mercedes-Benz G4 (W 31 series)

Heavy-duty offroad car, developed for the German army
Produced from 1934 until 1939
Number of units produced: 57
Today, three cars still exist which are considered absolutely authentic. Other units still exist but may include rebuilt cars and imitations, as is the case with other rare Mercedes-Benz classics.
The G4 owned by the Spanish royal family

Model year: 1939
Ordered by the German Reich’s Chancellery in Berlin
Present for General Franco
Today part of the automobile collection of the Spanish royal family
Serviced and maintained by the Royal Guard at the royal El Pardo palace in Madrid
Restored at the Mercedes-Benz Classic Center from September 2001 until December 2004
Order: repair of the technical components, no restoration work on bodywork, interior appointments and soft-top to retain the patina and originality of the car. Old and original components were retained whenever possible. Non-original components were replaced and reproduced on the basis of old blueprints.

Technical data: Mercedes-Benz G4, W 31 series, 1934 – 1939

General data:
Wheelbase: 3100 + 950 mm
Front/rear track width: 1620/1570/1570 mm
Dimensions (length x width x height): 5360-5720 x 1870 x 1900 mm (with soft-top)
Turning circle: 17 meters
Weight: approx. 3700 kg (in ready-to-drive condition)
Permissible gross weight: 4400 kg
Top speed permitted by the tires: 67 km/h
Fuel consumption: 28 liters/100 km (urban), 38 liters/100 km (offroad)
Fuel tank capacity: 90 liters, on some units 140 liters

Engine
Daimler-Benz M24 or M24 II eight-cylinder in-line engine
Total displacement: initially 5018 cc, later 5401 cc
Bore x stroke: 86 x 108 mm / 88 x 111 mm
Output: 100 hp / 110 hp at 3400/min
Torque: 28.8 mkg at 1400/min
Compression ratio: 1:5.6 / 1:5.2
Mixture formation: one double carburetor
Valves: overhead, lateral camshaft, driven by spur gears
Cooling: pump, 26 liters of water
Lubrication: force-feed, ten liters of oil
Battery: 12 V 60 Ah / 12 V 105 Ah
Alternator: 130 kW
Starter motor: 1.5 hp / 1.8 hp

Transmission
Four driven rear wheels, two self-locking differentials
Clutch: single-plate dry clutch
Transmission: four-speed manual and countershaft transmission
Ratios: I/4.10, II/2.21, III/1.49, IV/1.00
Drive ratios of countershaft transmission: road/1.00, offroad/3.06

Chassis
Box-section frame
Front wheel suspension: rigid axle, semi-elliptic springs
Rear wheel suspension: two rigid axles, one semi-elliptic spring for two wheels on each side
Steering: helical spindle
Brakes: dual-circuit system, hydraulic with vacuum assistance, acting on front and rear wheels; mechanical hand-operated parking brake, acting on front wheels
Lubrication: central
Wheels: steel disc wheels with drop center rims, size L 4.00 F x 17; with self-sealing tires: size 6.00 F x 17
Tires: 7.5-17 with offroad tread (normal or self-sealing)