A history with pulling power: Mercedes-Benz all-wheel-drive vehicles
Stuttgart
Aug 02, 2011
Agricultural giants: the MBtrac sets standards
  • Agricultural tractor based on a highly intelligent concept
  • Various versions delivered all over the world
  • Production discontinued in December 1991
The idea pursued by the team under Gustav Krettenauer, an agricultural engineer at the Daimler-Benz plant in Gaggenau, from 1967 onwards was to develop a high-performance tractor for as wide a range of applications as possible, which could be easily operated by one person and would be based on the well-proven concept of the Unimog. High torque at low speeds was the major requirement in large-scale agriculture. At the time a restructuring process was under way in the agricultural sector, when consolidation and mechanization meant that fewer and fewer farms were producing more and more. And anybody wanting to withstand the competitive pressure needed to employ personnel and machinery more cost-effectively than ever.
The MBtrac concept was guided by the following principles from the start: like the Unimog, the tractor was to have four driven wheels of equal size, and in the interests of cost-effectiveness it should adopt as many parts as possible from the Unimog. With a maximum speed of 25 km/h, the front axle drive was to be selectable while on the move, with differential locks on both axles. With the driver’s seat located in the middle, the majority of the weight was to be over the front axle to achieve an even weight distribution under full power. More powerful operating hydraulics than usual were to supply the power lifts at the front and rear. The vehicle was to have two power take-offs, and a third mounting area for agricultural implements was to be provided in place of a load platform.
The idea led to great controversy in Unimog circles, however the test department was able to design a prototype and commission its construction with the following specification as early as March 1968: ‘An initial prototype for a 60 hp agricultural tractor based on Unimog components is to be produced according to the requirements of the Unimog design and sales departments for the purpose of further discussions on the possible market launch of such a vehicle.’ In April 1969, a roadworthy prototype was available. It proved convincing, and development of the vehicle for series production commenced in August 1970.
Frame and front axle design similar to a truck
Painted in light pebble grey with red wheels and wings, the first MBtrac 65/70 was presented at the International DLG Agricultural Technology fair in Hanover in 1972. The model designation was derived from the engine output, as its four-cylinder OM 314 developed 48 kW (65 hp according to DIN or 70 SAE hp). The MBtrac differed substantially from conventional farm tractors in several respects.
The monolithic construction principle which had been usual since the 1920s, where the engine block and transmission housing were part of the supporting structure, was replaced by a light, flexible frame of U-sections with tubular cross-members to which various implements could be attached. There were mounting areas for these at the front, rear and behind the cab. The seat console was mounted centrally on the frame members. A rigid rear axle ensured maximum lifting power and precise implement control, while the sprung front axle with shock absorbers provided exceptional comfort.
A cab with exemplary comfort
The enclosed cab, which was located at the vehicle centre for low vibration, generally provided much better working conditions than was usual in the agricultural sector at the time, with wide, slip-resistant steps for ease of entry. The driver was protected from dust and weather on an air-sprung seat, and even air conditioning was available on request. Clearly and ergonomically arranged instruments and controls simplified operation, and the central cab provided an excellent view of all the mounted implements.
Above all, it was safe: the plant had this and subsequent cabs subjected to stringent tests – such as the pendulum impact test – by the test department of the German Agricultural Association in Groß-Umstadt near Darmstadt, and it passed them all with flying colours. Dispensing with a rollover bar was a first in tractor engineering: the layout of the structural sections ensured that the survival space remained intact if the worst happened.
This first MBtrac scored points with a whole range of advantages: the rear wheels followed the depression created by the front wheels (multi-pass effect), for example, while high torque was combined with four wheels of equal size and a low ground pressure. The portal axles with differential locks allowed a very high ground clearance, and the available speeds ranged from 0.14 to 25 km/h.
The first model from Gaggenau also excelled where comfort was concerned. Power-assisted steering eased the driver’s workload, and both the front axle and cab were sprung. A static axle load distribution of 60:40 per cent respectively to the front and rear axles was also an advantage, as it resulted in an ideal 50:50 ratio when operating with mounted implements. The use of a rigid rear axle was no accident either, as it allowed more precise implement control and more lifting power. Another new feature of the MBtrac 65/70 was that it could accept the implements designed for the Unimog with the help of its quick-hitch system.
Positive reception leads to an expansion of the range
All this met with great approval, and although the MBtrac was viewed with some suspicion by agricultural specialists, it certainly attracted enormous interest among farmers at the DLG show in 1972. There was a tidal wave of visitors to the stand, and eventually the stand management was forced to request additional security personnel from the plant in order to control the crowd. In fact the new vehicle was not even positioned in the centre of the stand, and only a modest sign reading ‘New Product’ drew attention to this minor sensation.
The Gaggenau sales personnel were able to leave the show with almost 350 orders in hand, even though the tractor was only due to enter series production in July of the following year. The plant had presented the new product in an unusual hurry, as Klöckner-Humboldt-Deutz was also exhibiting a new tractor named the Intrac at the DLG show. In contrast to the MBtrac from Mercedes-Benz, Deutz only offered four-wheel drive – which is nowadays standard in agricultural tractors – as an option for the Intrac. Moreover, the Deutz-Intrac still had wheels of different sizes.
Gaggenau produced 520 tractors in 1973, and by the end of 1975, 2714 units of the first series had left the production line. It was already clear from the start that the MBtrac had a potential that went well beyond the agricultural sector. Accordingly, and before the start-up of series production (which began in August 1973), Mercedes-Benz also presented the MBtrac at the world’s largest fair for the construction industry, namely ‘Bauma” in Munich, where it exhibited an MBtrac with a vibratory compactor. The manufacturing companies Schaeff and Hoess also presented an excavator/loader based on the MBtrac. The new concept also received a positive response from the construction industry. The MBtrac was always a convincing proposition when the high road speed and extreme off-road capabilities of the Unimog were not required.
Full speed ahead for a full model range
Encouraged by this success, Daimler-Benz presented an even more powerful tractor just two years later, at the 1974 DLG fair. The general view was that an entire vehicle family should evolve from the basic model if the concept was to endure. The MBtrac 95/105 was exhibited at the fair with light green paintwork, though things did not progress beyond a prototype at this stage. Instead the original MBtrac 65/70 was initially succeeded by the new MBtrac 700, equipped with the 48 kW (65 hp) engine of its predecessor, and the likewise new MBtrac 800 with an output of 53 kW (72 hp) from August 1975.
These were equipped with a slightly modified cab in which the roll-up tarpaulin at the rear was optionally replaced by a fixed rear wall with a wind-down window in the upper section. The vehicle’s radius of applications constantly increased, and by the end of 1975 more than 3000 units of the MBtrac had left the production line. They were not only destined for the agricultural, forestry and construction sectors, for equipped with front and rear trailer couplings as well as different tyres, the MBtrac soon also made a name for itself as an industrial tractor unit for trailer loads of up to 60 tonnes.
1976 marks the arrival of the heavy variants
At the SIMA fair, the largest French agricultural show held in Paris from March 7 to 14, 1976, Daimler-Benz was ready with the heavy MBtrac 1000 developing 70 kW (95 hp). At the DLG fair in Munich at the end of May, the engine, which had proved its worth in hundreds of thousands of vans, minibuses and Unimog vehicles, was shown with an increased output of 81 kW (110 hp), and the tractor was now called the MBtrac 1100. The engine generated its maximum torque of 363 newton metres at 1600 rpm. A turbocharged version with 92 kW (125 hp) and a torque of 393 newton metres was also available, and powered the MBtrac 1300.
This new heavy series was a completely new development, and had no components in common with the lighter MBtrac models, but in many respects the new, heavy models marched in step with the likewise new, heavy Unimog models of the 425 and 435 series. Their axles were not man enough for the power of the heavy MBtrac models, however, so the engineers developed a hybrid of the Unimog’s axles and the newly introduced planetary axles for trucks, and these proved highly successful in practical use.
The Minister for Agriculture Josef Ertl came to the Daimler-Benz stand in person on opening day, and praised the innovative concept of the MBtrac together with the considerable new investment involved: ‘There is a wealth of new agricultural technology to be seen at this year’s DLG fair, and Daimler-Benz has not least contributed to this with an impressive expansion of its tractor range. To make this possible, more than 70 million Marks have been invested in the Gaggenau plant, where the Unimog and MBtrac are produced.’
Externally, the completely new MBtrac 1100 and 1300 were distinguishable from the light MBtrac 700 and 800 series by their larger engines: while the four-cylinder unit had a displacement of 3.8 litres, the six-cylinder engine had 5.7 litres and could not be accommodated under the bonnet of the tractor without certain modifications. As there was no room there for a silencer, a fat exhaust pipe encased in a black surround pointed up at the front like the smokestack of a locomotive. The upper surface of the long bonnet and the slightly angled radiator grille were also painted black.
Low ground pressure, high ground clearance
The MBtrac was so designed that 60 per cent of its own weight was carried by the front axle and 40 per cent by the rear. Under load, i.e. with implements mounted at the rear or when pulling a plough or other agricultural equipment, this produced an equal weight distribution to both axles. The four wheels of equal size provided maximum traction, with a low ground pressure and a high ground clearance of around 500 millimetres. The four-wheel-drive system also reduced slip, a particularly noticeable advantage on wet clay soil. Naturally there were inter-axle and inter-wheel differential locks which could be engaged at any time.
In certain circumstances – for example when harvesting maize or beet – it could be advantageous to push rather than pull the harvesting implement. If this was mounted at the front, the tractor was more manoeuvrable, practically drove itself and made best use of its roughly 13-meter turning circle. To this end, the entire unit consisting of the driver’s seat, steering wheel, instruments and pedals could be rotated by 180 degrees.
Both these advantages – pushing implements in the reverse direction and operating with high loads on wet, muddy terrain – were only possible thanks to a newly developed, flexible and highly sophisticated, synchronized range-change transmission. In its basic version this consisted of a six-speed main gearbox and an eight-speed working gearbox, and this could be optionally augmented with eight crawler gears by means of a downstream planetary gear set. An optional overdrive gear could also increase the maximum speed from around 25 km/h to 40 km/h. All the gears could also be used in the reverse direction by simply operating a lever.
Power take-offs, compressed air and hydraulics for optimal power transfer
In addition to sheer pulling power, versatility and ease of operation were essential for the cost-effective use of the tractor, which was required to perform a wide range of duties with many different items of equipment. This is where the hydraulics, pneumatics and power take-offs on both sides met virtually all requirements. A transfer case flanged directly to the engine transmitted the power to the power take-offs, which could be individually or jointly activated, even under load and independently of the power transfer to the running gear, by means of a pneumatically operated clutch.
A compressed air system with hydraulic transfer controlled the four expanding brakes. The four-wheel drive, differential locks, parking brake and, if specified, a combined single and dual-circuit braking system for a trailer were also operated pneumatically. The hydrostatic hydraulic steering with its own oil circuit ensured that steering the large front wheels was child’s play even on difficult terrain.
The developers also paid particular attention to the control hydraulics. With a working pressure of 200 bar, the pump had an output of either 45 or 60 litres per minute. In addition to the connections for a rear power lift and an additional implement, plug-in connections were available for two additional control units with separate return lines, which meant that implements could be operated from all three mounting points. With an oil reservoir of 52 litres the maximum bleed volume was 45 litres, enough for even the largest hydraulic cylinders used by mounted implements.
Standard equipment in the MBtrac 1100 and 1300 included a rear-mounted, conventional power lift (maximum lifting power 65,000 newton with a mechanical Servotrak wheel pressure booster. Depending on the cylinder cross-section, the standardized three-point linkage was capable of bearing 35,000 or 50,000 newton. An electronically controlled power lift with tractional resistance, positional and combined control, such as would be needed for mounted or coupled ploughs, cultivating or harrowing, was available on request. A laterally stabilized front power lift with a lifting power of 12,000 or 25,000 newton could also be ordered.
Customers immediately recognize the benefits
The MBtrac 1100 and 1300 received a highly positive reception. The attributes of the new vehicle were particularly appreciated on the heavy, wet soil found for instance in the marshy areas of northern Germany or during beet-harvesting in August: ‘You should have seen us last year. You would not have believed your eyes! The trailers loaded with beet were often up to their axles in the mud, but the MBtrac still managed to pull them out. That’s the kind of pulling power – plus all that comfort – that we need,’ said Josef Schiele in Hamlar/Donauries, who purchased an MBtrac 1300 in May 1977.
Overseas, in road building or in the forest: the MBtrac makes its mark everywhere
Whether harvesting beet or drilling maize, planting cabbages, potatoes or wheat, or mowing rape, the heavy four-wheel-drive tractors were immediately put to a wide range of agricultural tasks which they performed better than their conventional counterparts. The MBtrac also made its mark overseas: in 1980 one MBtrac 1300 was delivered to Guatemala, for example, where it made itself useful in the cotton-fields.
In Australia, where even then the average farm measured between 250 and 500 hectares – compared to a modest 19 hectares in Europe –, the new tractor immediately met with great interest. Barry Cooke, a sheep farmer in Myrup, Western Australia whose company Prime Exporters sends 280,000 lambs to the Middle East each year, acquired three MBtrac 1300s for feed harvesting on February 9, 1979. In addition to the pulling power, his buying decision was based on the multiple front and rear mounting facilities, which enabled him to streamline his working procedures considerably.
The heavy tractors were equally convincing in the road building sector: when the MBtrac 1300 won the pulling power test at the Orange Field Days for the third time running, Australia’s largest road building contractor Coates Hire also purchased three of these tractors in 1980. These pulled road-rollers weighing 16 tonnes over rocky ground at 20 km/h, and performed tasks that only tracked vehicles had previously managed. Nothing seemed beyond their capabilities. In 1979, during the construction of the motorway ring around Hannover, an MBtrac 1300 with mounted cage wheels pushed its way across marshy terrain where other vehicles would long ago have given up the ghost.
At the Interforst fair in 1978, Daimler-Benz also presented the model MBtrac 1100 F and 1300 F forestry tractors. These were similar in construction to the successful, lighter MBtrac 800, but had different dimensions. A number of design changes such as full underbody protection or a hill support were adopted from the MBtrac 800. Both tractors were available with a 2x6- or 2x10-tonne double drum winch.
During particularly heavy snowfall in the winter of 1978/79, farmers in Lower Saxony simply got their MBtrac 1300 out of the shed and set off to clear the roads. Nor was industry slow to recognize the advantages of the MBtrac 1300. At the Krupp plant in Rheinhausen it was used around the clock to tow 70-tonne trailers of semi-finished steel from the rolling mill to the unloading cranes. After the MBtrac 800, the Thyssen stainless steel plant in Krefeld also used the MBtrac 1100 and 1300 in three-shift operations.
The MBtrac 1300 was well received from the start. Daimler-Benz had sold 3000 four-wheel-drive tractors in the first two and a half years since series production began in mid-1973, and this number rose to 10,000 by April 1979. A large proportion of these was accounted for by the MBtrac 1300, which was in many ways superior to other tractors in its field. The reactions of satisfied farmers, and also feedback from foreign countries with enormous agricultural acreages, indicated a promising future.
New flagship: the MBtrac 1500
Soon even the 92 kW (125 hp) of the MBtrac 1300 was no longer at the cutting edge; so in 1980 Gaggenau presented a new flagship model with a turbocharger and 110 kW (150 hp): the MBtrac 1500. Four years later the MBtrac 1300 and 1500 were even awarded a gold medal after practical trials by the Royal Agricultural Society in England. 250 units of the MBtrac were sold there in 1983 alone, three times as many as in the previous year, although the market as a whole was declining. And the trend was continuing.
Viewed in the long term, however, the same developments that had assisted the rise of the MBtrac, and which it in turn encouraged, namely the consolidation of agricultural holdings and increasing rationalization with a heavily reduced number of farms, also marked out its limits. Tractor registration declined by 22 per cent in Germany between 1980 and 1986, and the figure was almost 30 per cent for Europe as a whole. At the same time the number of four-wheel-drive tractors increased. This confirmed the correctness of the MBtrac concept, though this had meanwhile also been adopted by other manufacturers.
Constant improvements keep the MBtrac up-to-date
For these reasons, annual volume never exceeded the roughly 3000 units already achieved by the MBtrac during the 1970s. Nonetheless the plant always kept the MBtrac up-to-date. Together with the flagship MBtrac 1500, the MBtrac 700 S was introduced in 1980 as a new version of the light series. In the same year it was joined by the MBtrac 700 K, whose standard load platform made it particularly suitable for municipal services. The MBtrac also acquired a roof hatch from the New Generation 80 trucks, which provided the emergency exit required by export countries such as Sweden and Finland.
Turbocharging was also introduced in the light MBtrac 900, whose OM 314 now developed a rated output of 63 kW (85 hp). This model was only produced for a short time, however, as it was replaced by a completely new generation in 1982. This was the start of a major Mercedes-Benz product initiative in the increasingly competitive tractor market. Traditional names such as Lanz-Aulendorf, Fahr, Kramer and many others had already passed into oblivion or diversified into other sectors. The MBtrac remained though, and like the Unimog, it had developed from an agricultural machine into a jack-of-all-trades.
Major product initiative to mark the 10th anniversary
The product initiative started with the new 441 series, whose first representative, the MBtrac 1000, was presented at the DLG fair in Munich in May 1982, closing the gap between the MBtrac 900 and the MBtrac 1100. It was powered by the well-proven six-cylinder OM 352. The cab had been completely redesigned, although the doors were directly adopted from the heavy series.
Externally the new series was distinguishable by a more modern bonnet design, while the driver enjoyed refinements such as improved noise insulation, a hydraulic suspension seat and overpressure ventilation. Moreover, the designers had now moved the selector levers and other controls formerly located between the driver’s legs to a more user-friendly position on the right. Almost 500 customers immediately signed a purchase order at the fair.
The maximum speeds available for this new MBtrac were 25, 30, and 40 km/h, and in the same year the plant added a forestry tractor variant named the MBtrac 1000 F. Only a little later, to mark the tenth anniversary of the MBtrac, the revised models of the light 440 series were introduced: the new MBtrac 700, 800, and 900 turbo all featured the same, particularly comfortable cab of the MBtrac 1000, a more modern bonnet design and bright green paintwork. The technical features and controls had also been comprehensively modernized.
Daimler-Benz looks for a partner
The new MBtrac range - more extensive and modern than ever – was an impressive line-up with three model series and seven basic models. Europe’s agricultural machinery industry was clearly heading for a major crisis, however, and sales declined dramatically in the mid-1980s. There was a flurry of mergers leading to increasingly large conglomerates and a major price war.
Daimler-Benz too began to look for a partner in this increasingly difficult business. Even in 1986, Gaggenau was still producing just under 3000 MBtrac units, performing bravely in terms of registration figures and market share, however even this respectable volume failed to meet in-house targets.
Just as Gaggenau was presenting a completely new series of eight MBtrac tractors in April 1987, Daimler-Benz joined forces with Klöckner-Humboldt-Deutz to form a joint venture named Trac-Technik-Entwicklungsgesellschaft (TTE). The aim of the new partnership was to ‘safeguard the future of this tractor concept (four-wheel drive, four wheels of equal size) and develop this tried and tested concept in the interests of customers.’ The intention was to produce a joint inter-company Trac family with 51 to 147 kW (70 to 200 hp); with 60 per cent of the shareholding, KHD had more say in the new business although the MBtrac was a more convincing proposition than the Intrac.
The most important new features of the last MBtrac generation presented in 1987 were a changeover to the OM 364 and OM 366 engine series, the addition of the MBtrac 1100 to the medium series and a particularly thoroughly modernized heavy series, with the new models 1300 turbo, 1400 turbo and 1600 turbo. The MBtrac had reached the pinnacle of its career and was able to cater for any application with a full model range.
Intercooling boosts output to 132 kW (180 hp)
The fall of the Berlin wall proved a further benefit to the concept, as the agricultural production cooperatives in the new German states held enormous acreages after reunification – and powerful tractors were just what they needed. As a particularly powerful vehicle and new flagship model, Mercedes-Benz introduced the MBtrac 1800 Intercooler with a turbocharged, intercooled engine at the 1990 Nordagrar fair in Hanover. This was mainly distinguishable from the other heavy MBtrac models by a small recess above the radiator and larger tyres.
Only 190 of these MBtrac 1800 Intercooler models were built, however. Although TTE was working at full speed on a joint successor to the Deutz Intrac and MBtrac, and both partners had agreed on a shared concept with a central cab, bonnet and six or twelve-speed power shift transmission, but bringing this into production no longer appeared possible. In 1991, a completely new Unimog series based on new components entered production in Gaggenau, and the fate of the no longer compatible MBtrac was sealed.
Estimates of costs and potential sales by TTE showed that a succeeding generation would need to be around ten to 15 per cent more expensive than the current MBtrac generation, which was not profitably feasible in the market. Accordingly production in Gaggenau ceased on 17 December, 1991, after a period of 20 years and total worldwide sales of 41,365 units.
 
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