The O 303: modular buses

Oct 30, 2008
  • Functional cubic design
  • Six wheelbases, seven lengths
  • Power from large-displacement V-engines
The bus of the Mercedes-Benz O 302 model series, with its clear-cut lines, proved to be a big hit for a full decade, even clearly topping the big successes of its predecessor, the O 321 H. So what could be more sensible in developing a successor than to perpetuate this success? It was not only the name, O 303, that pointed to the strong affinity between the two bus generations at the launch in 1974. The looks of the O 303 also clearly built upon the predecessor.
The front end adopted the clear-cut design of the predecessor. The border around the star and the again rectangular headlamps were even a bit more straightforward (as time went on the border was dropped and replaced in 1982 by an embossed plastic part); a swage line pressed into the sheet metal took the place of the shiny decorative band running across the front end and framed the turn signal lamps. The windshield rose almost perpendicularly, its lower front edge again forming a line with the window of the door. During the first years a narrow vertical strip still divided the windshield.
The front end together with the driver’s area was again set off a bit at the top; the bumper was no longer attached to the body but formed a single unit with the front apron. And the curved, double glazed side windows (now without a chrome frame; depending on the paint color the window guides often were painted a discreetly contrasting dark color) extended into the roof area on all variants. The center or rear door again had an additional window at the top.
Whereas the plump rear end of the O 302 with the quarter windows before it was reminiscent of the design idiom of the 1950s, the rear end of the O 303 rose up almost straight as a ramrod. A functional and cubical shape characterized the O 303 – with the exception of the roof edge, curved to afford passengers a good view. If we compare it with the cars of those years, it was more Stroke Eight and W 123 than S-Class – a precondition for a long lifecycle.
Concentration on interurban, combination and touring service
Just like the trucks of this period the new O 303 bus made use of a modular system. The O 303 can be regarded as the prototype of this rational construction method. With six wheelbases and even seven lengths the bus covered all conceivable size variants from 8.7 to 12.0 meters – there were never more, and there probably never will be more. From nine to 15 seat rows, there was everything that bus companies in Germany and abroad might be able to use. However, the O 303 concentrated on interurban, combination and touring service – urban buses long since were the domain of the
O 305 standard bus. For rural service there was the O 307 derived from it. It satisfied the modest demands on looks and comfort.
The Mercedes-Benz O 303, in contrast, was just the right bus for the private coach operator: interurban service during the week, excursions on weekends were the work cut out for the O 303 in its simpler variants for combination service. For pure touring service the upscale editions with high floors and correspondingly large luggage compartments in their bellies, like the O 303 RHH, later RHS, were responsible. And with the short variants O 303/9 and O 303/10, for the first time Mercedes-Benz offered a handsome club bus for small groups taking exclusive tours.
But precisely private coach operators missed another important variant during the
O 303’s first years: the sales range lacked a long-haul high decker for long-distance travel to tourist destinations. These coaches – recognizable by a central entrance whose door does not extend beyond the window sills because the body is so tall – were available from all renowned touring coach manufacturers in the 1970s. They had much stowage space, and for travel to faraway places they, of course, also had compact galleys and toilets. Mercedes-Benz didn’t supply high deckers until 1979, when the two longest variants of the O 303, the 14 RHD and 15 RHD were launched. They measured 3.4 meters tall, whereas the other variants – like the predecessor, the O 302 – rose to a height of just over three meters.
A close affinity of the engines to those of the trucks from Mercedes-Benz was one feature of the modular system of the new O 303. Here the O 303 profited at its premiere from the “ New Generation (NG)” that had been presented just a year earlier. Whereas the O 302 was driven by relatively weak in-line six-cylinder engines with power in rather short measure, large-displacement V-engines now saw use in both buses and trucks. In the first few years these were naturally aspirated engines, without exception; Mercedes-Benz didn’t rely on turbodiesel engines until the second half of the long life of the O 303.
Installed in the rear end of the compact variants of the O 303 with lengths up to 10.6 meters were compact V6 engines with a displacement of 9.6 liters; 12.6 liter V8 powerplants and even the 16 liter V10 usually powered the two longer editions. Concurrent with the launch of the RHD high-decker and the introduction of the undivided windshield, a new engine generation arrived on the scene in 1979. The V6 now got 159 kW (216 hp) out of a displacement of eleven liters; a V8 with 14.6 liters displacement and 206 kW (280 hp) now powered the medium-sized and larger variants. A turbocharged V6 with 184 kW (250 hp) and a turbocharged V8
(243 kW/330 PS) finally arrived in the mid-1980s. In the outgoing 1980s engine power was increased again; the strongest variant then developed 260 kW (354 hp).
Connecting rod journals are moved to improve the smoothness of the V6
While the V8 was both beefy and smooth and enjoyed great popularity, the V6 never really reached the hearts of bus companies and drivers: the rough running characteristics just didn’t seem to go together with comfort-enhanced coaches. Further development of the six-cylinder in the course of the eighties – the connecting rod journals were moved to obtain more even firing intervals – then corrected this impression.
The powertrain employed five- and six-speed transmissions or an optional automatic transmission. From 1987 on Mercedes-Benz also offered the semiautomatic electronic/pneumatic gearshift system EPS (=electronic power shift). This early stage of today’s automated gearshift systems still had a clutch pedal, but on the right side of the driver’s seat a joystick replaced the conventional gearshift lever with its long shift travel. Now a tap was all that was needed to shift.
As with the engines, Mercedes also took a conservative approach to the suspension of the O 303: air suspension was an obvious choice for the O 303, but the bus – “same as ever” – had a rigid front axle, with drum brakes on all wheels. As before, the design of the bus was based on a self-supporting frame-floor system. On the other hand, in 1985 Mercedes-Benz created quite a stir when it became the first bus manufacturer to have an anti-lock braking system. Retarders additionally were available as special equipment.
Compared with the unsophisticated driver’s position of the O 302, the O 303 had a veritable cockpit. The large surface of the instrument panel was curved, but the instrument setup –a large speedometer and instrument cluster and a smaller rev counter in between – was rather conventional.
The Mercedes-Benz O 303 reached the end of its days with a manageable but very versatile range of coaches. The variants KHP-A and KHP-L, with six lengths, covered the interurban lines and combination service sector. The RHS could be had in two short variants as a club bus; the two lengthier variants served as raised-floor touring coaches. The RHD high decker was available in two lengths. And there were editions of the O 303 alternatively with rear or center door for the passengers and different seats.
Up to date 18 long years
The O 303 as a reliable and conservative vehicle was perfectly welcome to coach operators: with lavishly equipped special models with paint jobs somewhere in between elegant and smart, the Mercedes-Benz O 303 was kept alive and fresh over a lifetime that must be some kind of a record. In 1992, after 18 long years, it finally went into well-deserved retirement. Actually, for this derivative of the O 302 this was enough for two bus lives. Even more than a dozen years later one still comes across very well preserved O 303 coaches on roads and in bus parking areas. And while at the end of its long career the signs of ageing definitely were perceptible, as an oldie approaching classic status it now cuts a very sympathetic figure.
The countable result at the end of a long career was even a new world record: 38,018 buses, about two thirds completely built-up buses and one third chassis, came into the bus world in almost two decades.