Seddon Atkinson 400-series tractive unit at 32 tons gcw
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by Graham Montgomerie pictures by Dick Ross
BECAUSE Seddon Atkinson were able to let us have an early model of their new 400series tractive unit for test well before its official launch this week, we were able to take the unusual step of subjecting it to Continental conditions— now becoming relevant for an increasing number of British Operators.
We also drove it over our full England-Scotland-England operational trial route and tested its performance at the MIRA proving ground, so this report is the fruit of an unusually large mileage spread over more than seven days.
For the Continental trial we devised a route which started and finished at Calais and which involved driving across Northern France into Germany, turning due north alongside the border with Luxembourg, then across Belgium and back into France.
Although the new truck performed well in most respects, and eventually produced excellent mpg and outstanding braking figures, the report of the Continental test must be coloured by the peculiar behaviour of the Cummins engine. Nominally rated at 250 horsepower the unit never approached the level of performance I would normally associate with this output and returned an overall fuel consumption of 1.55 km/1 (4.4 mpg). Because these results could hardly be said to be typical of a Cummins engine, the unit was sent back to the Shoitts factory where the governor was found to be cutting in early. A flat spot in the power curve was also discovered and reotified.
With the truck now meeting its on-paper specification I took it round the normal CM Scottish test route, where it removed all of my previous criticisms as well as returning an overall fuel consumption of 2.33 km/1 (6.6 mpg) which is slightly better than the norm for this route.
In the cab
The Seddon Atkinson interior was furnished in a light tan colour which made a change from the usual black although I am not sure how long the interior would retain this colour in normal usage. The instrument panel was well laid out from the aesthetic point of view but proved difficult to scan quickly as the panel was so symmetrical with so many similar dials. I thought that this situation would improve as my familiarity with the truck increased but I still had the same problem after some 1400 miles at the wheel.
Apart from the gearshift layout which I found initially confusing and which I will enlarge upon later, the control positioning was good although the seat rake adjustment wheel was positioned between the seat and the cab entry grab handle which made it physically impossible to get one's hand into the gap to adjust the seat — Seddon Atkinson have altered this for the production models. The seat itself was cloth-covered in the centre sections, a feature I personally consider essential for a longdistance truck.
The location of the parking brake control on the prototype at Earls Court last year had been criticised by the bunch of BRS drivers I accompanied around the Show, but in practice I did not find it so obstructed by the gear lever as I had feared.
The forward visibility from the new cab was really excellent, with a nice high leading edge to the roof line which gave a good area of useful vision. Unfortunately in the wet the wiper spread was inadequate in the vertical direction which meant that in rainy weather I had to look through the unwiped upper portion of the screen.
At the top of the side windows, forward and rearward opening vents were fitted for cab ventilation which worked reasonably well but the bar dividing them from the main side window obstructed rear mirror vision.
The Continental test
After a day of frustration at Dover trying to convince the customs officials that concrete test weights were not contraband, we arrived in Calais in the late evening ready for an early start the following morning.
My first session at the wheel of the Seddon Atkinson was punctuated by problems caused by my unfamiliarity with the gear selection pattern. The box was a standard Fuller RTO 9509 which has a different shift layout anyway, without the usual H-pattern. On a normal RTO 9509, second gear, which is .normally employed for starting (first being a crawler), is away from the driver and forward, the rest of the gears following in an anti-clockwise sequence — a sequence with which I am very familiar. But on the Seddon Atkinson an extra linkage has been installed to facilitate cab tilting which has had the effect of rotating the shift pattern through 180 degrees with second gear towards the driver and back. It took a little while to get used to this pattern and avoid trying to start off in fourth— or, worse, going across the range change from eighth to third instead of from sixth to fifth. Happily this situation did not last long, although I foresee problems in service with drivers switching from standard RTO boxes to the " reversed " SA layout and back again.
The first section of the route led from the docks at Calais through St Omer, Bethune and Arras towards Reims and although the roads were very flat the Seddon Atkinson just would not pull top gear. At peak revs in eighth I would select top, which the Cummins would only pull for about 200 metres before I had to change down again—and this was on a level road.
On one section we took to roads which were somewhat narrower and bumpier than we would have liked but at least it provided the opportunity for testing out the truck suspension which took a real hammering on the appalling surface but passed little of the movement through to the driver, The ride was excellent on such surfaces but it suffered from a common fault with trucks on smooth sections where it tended to wallow over the longer deflections.
Travelling through this part of France with its Great War associations meant a great deal of constant-speed running and under these conditions the in-cab noise level was acceptably low. If full throttle was needed, however, the in-cab noise rose appreciably, making across-cab conversation difficult.
From the customs post at Saarbrucken the next stage of the test led north through West Germany virtually alongside the border with Luxembourg. This was the first chance the Cummins engine had had to really stretch its legs as the road now began to wind up towards Trier and farther on up into the Eifel mountains. In spite of the disappointing performance on the level, the Seddon Atkinson passed everything in sight on the slopes. But, as soon as we were on level ground and around 75 km/h (47 mph) was reached the vehicle just ran out of steam. The curious thing about this engine was that there was never any trace of black smoke either on full or part load even though the performance was so erratic.
The hilly country in this extreme corner of Germany meant that the effectiveness of the exhaust brake could be evaluated. In this sort of country with its succession of 1 in 7s such a device was really invaluable — it was definitely not the place to have to contend with brake fade ! The particular exhaust brake on the Seddon Atkinson was of the slide valve type which was set on "automatic "—ie it functioned as soon as the throttle was released. I did not take to this arrangement as it tended to slow the engine too quickly on upward gearchanges, so I preferred to leave the brake switched off and use the manual override switch to put it back on. This arrangement worked well, though the switch was rather low for comfortable use.
The exhaust brake itself worked extremely well. It even managed to begin slowing down the 32-ton combination going down a 1 in 10—most exhaust brakes cannot even hold the speed constant on such slopes. On the debit side it made such a shattering noise in operation that I only used it in open country.
The new truck was fitted with a Dynair thermostatically controlled fan, standard on Cummins and Roils models of the Seddon Atkinson range, which helped to maintain the reasonable in-cab noise level. Initially I was rather unfair about the device because of the noise the fan made when it was engaged but then I remembered that the installation was in fact doing a grand job in preventing this noise from being present all the time. The first time the fan came in was on the long uphill slog out of Saarbrucken and it gave me quite a fright because of the rapid increase in noise but it had the desired effect of bringing the temperature down rapidly.
The instrument layout on the Seddon Atkinson reminded me of the B series ERF I sampled last year, which is not really surprising as they use identical gauges, but whereas the Cummins 220 in the ERF ran extremely cool the 250 in the SA was exactly the opposite. The temperature gauge in both cases had a " red-white red " indicator with the " white " portion indicating normal running temperature. The ERF dial hardly moved from the cold segment but the Seddon Atkinson always ran verging on the " hot " portion with the Dynair cutting in immediately the n e e dle actually touched the red.
Crossing t h e German/ Belgian border at Aachen the road conditions changed to pure motorway with top gear (or at least 8th) being used right across Belgium with the exception of the urban sprawl around Brussels. The characteristics of this particular Cummins engine meant that, as in France, an occasional downchange was necessary to keep the speed up.
The last section of the Continental loop was on an A-type road from Ostend through Dunkirk and back to Calais and this was a nerve-racking session because the obligatory yellow lenses fitted to the Seddon Atkinson for the Continental run gave very little light.
The fuel consumption during the Continental road test and the related performance of the Cummins engine deserve a full report themselves. The overall fuel consumption for the trial which covered in total 1095km (680 miles) was 1.55km/1 or 4.4mpg. This low figure was not the result of either a poor high-speed result or low figures for the mountain sections. The A road, severe road and motorway sections all gave the same result.
When tested in its " Continental " form at the MIRA proving ground the acceleration figures were also well below average. As an example, the Seddon Atkinson at 32 tons gcw took a full 99 seconds to reach 40mph. One of its competitors tested recently took only 50 seconds to reach this figure—at 38 tons gross.
The fact that these were not typical figures was quickly borne out when we tested the vehicle, after attention to the engine, at MIRA again and round the Scottish operational trial route.
The second test
On the UK test the Seddon Atkinson was a completely different truck. Gone was the poor top end performance and the lazy acceleration and instead the vehicle now possessed the performance expected from 250 bhp.
At MIRA the time taken to reach 40 mph was trimmed from 99 to 54 seconds, a similar improvement being recorded throughout the speed range.
When put on the road course, the truck had no difficulty maintaining a comfortable cruising speed of around 55 mph on MI—a far cry from its performance in France. The hill-climbing ability could be categorised as "slow but sure" rather than particularly quick. In this respect the Seddon Atkinson could be likened to the Fiat 619. Taking the Carter Bar climb on the England/Scotland border to illustrate the point, the SA took 6 min 28 sec for the 2.93 km (1.82-mile) long slope with its average gradient of 1 in 13.5 which is on the slow side for this power output. Part of the reason was that the typical gear up this climb was fifth, which could be pulled at maximum revs with no difficulty. However sixth gear was just out of range— a splitter would have been useful in these circumstances.
Fuel consumption
With the power unit now functioning normally t h e Seddon Atkinson returned consistently good consumption figures over the 728-mile test route. On •the M6 motorway from Forton to Gretna the figure was 2.32 km/1 (6.55 mpg) for an average speed of 79.8 km/h (49.6 mph). The worst figure was between Rochester and Nevilles Cross which contains the long steep gradients of Rids-dale and Riding Mill and here the Seddon Atkinson recorded 1.58 km/1 (4.47 mpg), which is right on the average for this section.
On the 40 mph section of Al the new truck really excelled itself with 3.65 km/1 (10.3 mpg) for an average speed of just under 40 mph.
The overall fuel consumption for the whole course eventually came to 2.33 km/1 (6.6 mpg) which is slightly above the average. Max-capacity trucks tested over the Scottish route give an average consumption of between six and seven mpg with the occasional result outside this range and 6.5 mpg is the current par for the course.
Braking performance The stopping ability of the Seddon Atkinson was among the best I have tested, with average retardations of 0.6 g being recorded. Once again, as shown in many past CM tests, good brake balance between tractive unit and trailer proved its worth by making these stops incident-free, with little or no wheel locking. The braking distance of 26.8 m (88 ft I in) from 40 mph has been beaten by only one other truck over the past couple of years.
Summary From the driver's seat I was pleased with the way the new truck handled and any doubts concerning its performance were removed with the attention to the Cummins engine. The fuel consumption figures taken in England and Scotland are obviously a more realistic estimate of the truck's capabilities in service, though the Continental journey gave us an interesting opportunity to sample its handling abroad.
Existing Atkinson a n u Seddon drivers will certainly take to the new cab as it is such a vast improvement over the cabs it replaces. The makers' engineers claim that the kerb weight for the production versions of the 400 series will be well under the 6.6 tonnes (6 ton 10 cwt) of the prototype version which I tested.
Prices for the new Seddon Atkinson 400 series are given on page 4 of this issue. The model tested costs E11,150 excluding fifth wheel.