No-expense-spared restoration of a rare G4 1939 Mercedes Benz

The experts reconstructed several functions of the elaborate engineering and made them operational again. The original parts were 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 extremely good condition, 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 use modern lubricants into the axle housings because they would have had a corrosive effects on the bronze components in the differentials. The required oil also had to have a high shear resistance, so a lengthy search was undertaken for the best possible solution, with the experts ultimately deciding in favor of a special castor-based lubricant.

Finding the right tyres was a similararly exacting process. To be restored to a fully operational condition, the G4 needed eight new tyres including the spares and these were not easy to come by, given the required dimensions, the stability to match the vehicle’s high weight plus the appropriate offroad tread. Quite some time passed by before the right tires were located 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 unique 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 massive 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 were just not available “off the shelf”.

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