Mercedes-Benz 1626S/30 tractive unit at 32 tons gcw
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INTRODUCED in haulage form for Europe in May of last year, the first models from the new range of Mercedes-Benz trucks are now available on the UK market. Featuring the new cab designed with an eye on the environmental lobby, to look small externally without sacrificing anything in the way of driver space, the model expected to have the most penetration for Britain is the V8-engined 1626S/30. I have just taken such an example round the CM England-Scotland-England operational trial route with some very impressive results—including the Shortest round trip journey time ever recorded, coupled with an overall fuel consumption of 2.51km/1 (7.1mpg). The only real fly in the ointment is the initial price of £13,650 which puts the new Mere in the "super premium" category.
The new cab
When I first drove a "New Generation" Mercedes-Benz in Germany last year I was very impressed at the way the factory engineers had tackled the problem of presenting a less belligerent big truck appearance to the general public— all this with no reduction in interior dimensions over the old square cab. My recent road test confirmed all my initial opinions.
Visibility was first class—in the wet as well as toe dry, tor at long last a truck manufac turer has solved the problem of rear-mirror fouling in bad weather. An intake in the front of the cab feeds air through a duct in each door, which creates a high-speed layer of air alongside the cab, effectively preventing spray from the wheels reaching the side windows and mirrors. In the bad weather encountered on most of the 728-mile test I can report that the design was 100 per cent effective. Full marks to Daimler-Benz for solving this long-standing problem.
The control layout is simple and straightforward, and there are three main gauges on the instrument panel and the usual system of warning lights. A minor criticism concerned the siting of the heater controls which are obviously a hangover from the left hand drive models, being completely out of reach from the driver's seat.
The park/secondary brake control was not in the most convenient of places, but this criticism applies to nearly all the heavy trucks on the market. A stalk to the right of the steering column controlled a multitude of functions including headlight flasher and dip, horn, indicators and two speed wipers.
Performance
The V8 OM 402 engine in the Mercedes is part of the modular range which uses many components identical to the VIO and V12 series. Developing 188kW (256bhp) at 2,500rpm the engine is rather unusual these days in that it is naturally aspirated. At 32 tons gross as tested this gave the 1626 a power-to-weight ratio of 5.9kW/tonne (8bhp/ton), which made it quite a lively truck to drive.
I felt that the Mercedes was a trifle overgeared with its axle ratio of 5.22 to 1. At the MIRA proving ground there was insufficient room on the timing straights to check the speeds in top gear, but calculations based on the manufacturer's data sheets would seem to indicate a top speed of around 1181cm/h (73mph), which I feel is a bit excessive. Certainly on the motorways cruising at the legal limit there was plenty of power in hand.
On the other hand, the gearing caused no problems on the hilly sections of the route and the performance on the test hills at MIRA was satisfactory, the 1 in 6 restart being completed in fine style. I attempted the 1 in 5 but the Mercedes complained strongly in the clutch department although I think if it had been an emergency I would have persevered, with success.
On the motorways the new Mercedes is a .real flier, cruising at the 60 mark with around 2,100rpm on the clock. The noise level at this speed was good but not outstanding, a typical V8 throb predominating, although this did not cause any serious discomfort.
Economy
When it came to fuel consumption the new Mercedes really excelled itself. Around the CM Scottish route the norm for heavy artics is around the six and a half mark with some trucks dropping below six mpg. The 1626 returned the well-above average figure of 2.511(m/1 (7.1mpg), which I think surprised even the Mer cedes-Benz personnel who normally reckon one of their trucks to be run in at around 16,000km (10,000 miles) and who were rather apprehensive about the fuel consumption as the test vehicle had only covered some 5,200km (3,200 miles).
The fuel consumption was consistently better than average on each of the measured stages. On the motorways a figure of well over 7 mpg was recorded and the worst figure (as usual, measured over the hilly A68 section) was still relatively high at 1.88km/1 (5.3mpg). Many trucks reach the low fours in mpg on this part of the test.
In recent years this fuel consumption has only been bettered by one other 32-ton outfit and this was only by fractions. However, the Mercedes completed the test some three hours quicker, which I think more than compensates for a very minor increase in consumption. On our test the braking performance, however, was just not of the same standard as the rest of the vehicle. With a stopping distance of 40.2m (132ft) from 64km/h (40mph) the truck was definitely near the bottom of the list as far as recent road test comparisons go. The truck stopped evenly with no wheel locking, but the maximum efficiency recorded from each speed was just plain low. The Motometer test charts showed that this maximum efficiency was reached early on and maintained until the vehicle was almost stationary, which indicated how well balanced the tractor-trailer system was. But this could not counterbalance the fact that a maximum retardation, from 40mph say, of less than 60 per cent was just not good enough. The parking and secondary systems showed the same sluggish braking.
Obviously concerned at these results, Mercedes made a posttest check of the system and discovered that the load-sens ing valve setting on the tractive unit was for the Continental wheelbase and springs, not the UK spec—this could have created just the situation to result in the low figures we obtained.
On the road section of the test the brakes performed adequately, and I liked the feel of the pedal. The brake pedal of the Mercedes must be one of the smallest in use in a heavy truck, and the system was very progressive.
The effect of the exhaust brake was negligible whatever the engine speed which meant that at the bottom of some of the longer descents on the route the smell of hot brake linings was very noticeable.
The hydraulically tilted cab goes over to a maximum angle of 70 degrees for major service although this is not necessary for routine level checking. One excellent feature which in practice worked extremely well was the telescopic gear lever. When the cab is tilted the driver end of the gear lever remains in the cab-the rest of the lever extends telescopically. The advantage is, of course, that it eliminates the need for a hole in the floor, avoiding a noise-seal problem.
Whatever the road surface the ride of the 1626 was good. Multi leafed semi elliptic springs in conjunction with anti-roll bars are standard features both fore and aft which gave the driver a very comfortable time. But I wondered how much the leaf springs and anti-roll bars actually weighed on this model? The leaf springs are so substantial that I would think a change to the long taper-leaf type would give a significant weight saving.
I found the steering very responsive, but I did not like the " kick back" which occurred when crossing minor bumps in the road, for example cats' eyes on the motorway. On the Staffordshire section of M6 the tyre grooves in the slow lane are becoming more and more noticeable and these troubled the Mercedes when changing lanes.
The power assistance was good although I was not convinced about the large diameter of the steering wheel. However, this is required to meet German regulations in the event of a failure in the power-steering system.
One peculiarity of the suspension was the way the truck almost tripped itself up under heavy braking. The cab dip was very pronounced at anything above a very gentle deceleration and this gave the impression that the braking efficiency was better than it, in fact, was.
Summary With ever-spiralling fuel costs at the back of everyone's mind at the moment, the 1626 must come high on operators' short lists in terms of fuel consumption. When viewed alongside the highest overall average speed ever recorded for this route the results are most impressive.
Apart from the brakeswhich new load-sensing settings should improve-the Mercedes-Benz 1626 acquitted itself very well indeed. The vehicle is by no means cheap, at £13,650 including fifthwheel, as tested, and I must say that for this chassis price it should not be too much to expect electric screen washers as standard equipment instead of the rather feeble manual system fitted at present. But in other respects it is well equipped and finished.