The perfect base
For Daniel, off-road driving comes down to rock crawling events. However, according to him,
the best car for these competitions is a vehicle built by Mercedes-Benz, the Unimog truck
because of its portal axles that incorporate a hub reduction, its flexible ladder-frame, its
locking front and rear differentials, its coil springs and its excellent reduction. Luckily, in 2002,
Daniel found the perfect base: one Unimog 435 without bodywork. This Mercedes was an
ex-military armored truck. However, the French army wasn’t able to sell it with its reinforced
bodywork, so they had entirely stripped it. Moreover, it was the bargain of the century,
because he bought it for only $1,000!
Wheelbase: 94 inches only
Daniel wanted a 4x4 with a short wheelbase and without front and rear overhangs for the rock
crawling competitions. But, the standard Unimog 435 has a 128-inch wheelbase.
Consequently, Daniel cut the frame of his Unimog. The frame lost 46.8 inches in its total
length and, the wheelbase lost 31.2 inches. But, this cut was not easy! Daniel did not cut the
frame in its middle. The flexible ladder-frame of the Unimog twists in extreme off-road driving.
Consequently, Daniel removed the front suspension’s supports and repositioned them
correctly 31.2 inches further back. Thus, the frame keeps its capacity of torsion.
Ford transplant
To motorize his “proto,” Daniel didn’t conserve the Mercedes engine. He chose to install a
Ford Scorpio V6 2.8 engine. Daniel wished an engine with a lot of torque, but a block with
small dimensions. The Ford V6 engine, with its EFI injection and its central camshaft
answered perfectly these two desires. However, Daniel didn’t install it in the front position, but
above the rear axle instead. Thus, the weight of the block is based on the rear wheels,
ensuring the best motor function in off-road driving.
72 gear ratios
Daniel decided to assemble the V6 block with the two auxiliary gearboxes of the Unimog (a
standard Unimog doesn’t have transfer box, but an eight-speed forward and eight speed
reverse gearbox ). Our man chose a very difficult technical solution, but very advantageous.
He associated (mated — Ed) the Ford V6 engine and its Ford gearbox with the Unimog
gearboxes. Which Daniel mounted, back to front. The Input shaft of the Unimog gearbox
settles down (attaches — Ed) on the output shaft of Ford gearbox. However, with this
assembly, the front differential ring did not turn in the proper direction. Daniel thus had to
entirely alter the differential housing so that the differential ring migrated left to right. Another
problem occurred with this assembly as the front driveshaft had to lose 23.4 inches and the
rear had to extend by 7.8 inches. With these gearboxes joined together, Daniel has 72 gear
ratios, including one ultra low ratio. With this ratio, his prototype moves at the incredible
speed of 51 yards an hour. Another advantage of this assembly, the prototype is a front wheel
drive car, when the transfer is not engaged. A good thing for the steering angle! (i.e. front digs — Ed)
47 inches of wheel clearance (flex — Ed)
The suspension is still the same as a standard Unimog. After the amputation of the frame and
the consecutive loss of weight, the coil springs appeared too heavy duty for the rock crawling.
The wheels didn’t have much flex. The solution consisted of springs much more flexible. For
the front axle, Daniel chose models from a Peugeot 505 and, at the rear, he installed the
Unimog’s front coil springs. On the other hand, he preserved the four Unimog shock
absorbers.
Finally, one defect to be corrected
Then, Daniel had to solve two quite thorny problems: the adaptation of a new system of
power-assisted steering, and the installation of a separated hydraulic braking system at the
rear. Following the displacement of the axles, the steering column of the Unimog was too
long. So Daniel installed a shortened column, associated with a steering gearbox of a Ford
tractor.
To stop this prototype, Daniel mixed elements of various sources, like a brake master
cylinder from a Peugeot 205, pedals from Ford and flexible brake hoses off of a Lada and a
Mercedes. After tests, this mixture does not give satisfaction to Daniel. The brake power is a
little “weak” to stop this prototype, He can lock the rear wheels without locking the fronts. So,
Daniel is still looking to perfect his brakes.
Simplistic bodywork
Since Daniel bought this Unimog without bodywork, he had to create one entirely. It was not
problem for him, because he is a coachbuilder. He started by entirely making a roll cage on
which he installed some elements of bodywork. In order to preserve all the flexibility of the
frame, this roll cage is fixed only by two fixations on the rear of the frame. In front, the ‘cage is
based on two huge silent blocs. Thus, the frame can twist without the bodywork blocking this
phenomenon. Once the bodywork was in place, Daniel made two huge bumpers of tubes of
120 mm (diameter). Result; approach angle and departure angle are beyond 90°. Now, Daniel
had to paint his prototype. He chose sand with black spots, because, if, one day, Daniel
spoils the painting, he can easily add a spot. It’s not a stupid idea!
Off-road’s King
Daniel needed two years, in his spare time, to conceive his prototype. But when you see it in
action, you are sure that Daniel was not wasting his time. The suspension works perfectly.
The wheels seem to stick to the ground. With its 47-inch wheel clearance (travel — Ed) and
locking front and rear differentials, he can continue his path just about anywhere. In the same
way, with its 22-inch ground clearance, its approach and departure angles close to 90°, its
94-inch wheelbase and its compact dimensions (body length : 133 inches, width : 76 inches),
he can attack a vertical step without risk. Furthermore, thanks to its precise steering and the
ultra low gear, Daniel can place the wheels where he desires and move very slowly. In areas,
(French for obstacles — Ed) he’ll be having a great time!
