I ROAD TEST: Ma.ck/Northern 32-ton-gross Artie A T one time it was
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considered that American-designed vehicles could play little part in the UK transport scene because they were developed for a completely different type of operation-4ong, straight roads and high speeds, compared with our country-lane type of highways and limited speeds. With the growth of the motorway network in the British Isles and the recent uplift in gross vehicle weights the differences are diminishing and, to prove that American vehicles can be of benefit on British operation, Glasgow operator P. and S. Contracts Ltd. is successfully operating nine American Mack 11-61RST six-wheeled tractive units with Northern NTC-N22 tandem-axle semitrailers at 32 tons gross. One of these out-fits was loaned to "The Commercial Motor" by the operator for a full road test and the advantages of the vehicle for UK operation were confirmed.
It is particularly appropriate that a road test of this Mack unit has been completed at this time, for it is expected that plans will shortly be announced for an extension of the sates organization of Mack Trucks Worldwide Ltd. (the international sales company of Mack) with the setting up of a marketing organization and Service and spares facilitie's in this country under Mr. A. C. Southon, Mack sales director for the UK and Scandinavia. It is anticipated that twoand three-axle tractive units, either bonneted (like the test vehicle) or with forward-control Lilt cabs will be the models put forward for British operators. One particular advantage that can be offered by Mack in these days of long waiting lists for vehicles will be a two months delivery to specific order. • The test vehicle was powered by the Mack END 711 Thermodyne diesel engine producing a maximum net output of 195 b.h.p. at 2,100 r.p.m. and a maximum net torque of 578 lb. ft. at 1,250 r.p.m. The transmission incorporated a 10-speed Constant-mesh gearbox with a five-speed main gear train and direct and overdrive splitter. Wheelbase of the tractive unit was 12 ft. 2-5 in. and the fifth-wheel coupling was mounted 7 in. forward of the bogie centreline.
The engine is of conventional design, being a directinjection unit and naturally aspirated. Its fuel-injection system incorporates an automatic advance and retard mechanism which ensures first-time starting under the most severe conditions and provides for extremely smooth running. Among the many features of the END 711, which is one of a range of Therrnodyne units, are the Mack Air-Swirl combustion chamber and tuned manifold which together create excellent breathing and high thermal efficiency.
The fact that the engine was powerful on the road was shown during the road test. That these engines are extremely reliable has been proved by the operator. In 160,000 miles of operation—nearly always at 32 tons g.t.w. —the first four outfits put into service have needed nothing more than one fan-belt renewal between them. Brakes are expected to give a life of between 80,000 and 100,000 miles and, from what I saw of the liners on one machine which had run over 40,000 miles, this is no exaggeration. One asset of the engine is that an air starter is fitted. This is supplied by a storage tank charged to 100 p.s.i and the manufacturers claim that it will stay charged for an almost indefinite period. In the event of a leak developing, the tank can be charged by another vehicle or even from one of the tyres,
Four Brake Systems
In addition to the normal brake system on the outfit, there is the usual hand-operated brake valve in the cab for separate control of the semi-trailer brakes. These are actuated also through a pull valve when the tractive unit handbrake is applied. The emergency brake necessary to comply with the new C. and U. Regulations is therefore provided and, in addition, there is a small lever-2.5 in. long—which can be used to apply fully the whole braking system of the outfit. This is a modification for the UK, the lever being used in the United States to isolate the steering-axle brakes—a requirement in certain states.
The air system on the tractive unit consists of a watercooled compressor and brake valve and there are four reservoirs—a first or " wet " reservoir, a service-brake reservoir and an emergency-brake reservoir and, finally, that for the starter. All of these are isolated from each The Northern semi-trailers operated by P. and S. (one being used for the test) are 30 ft. long and 8 Et. wide. The running gear comprises a pair of Rubery Owen 22,500 lb. axles with four-leaf spring suspension. The brake units are S-cam operated and 16.5 in. by 8.625 in. The two-line air-pressure system has added to it a third, or auxiliary, line actuating 24 in. Berg-Protecto air chambers on both axles. In order to clear the rear of the tractive unit chassis the landing gear is mounted 11 ft. 4 in. from the front end of the semi-trailer. Because of this it has been necessary to reinforce the swan-neck section of the frame to prevent drooping when standing landed and loaded. The parking handbrake is operated by a ratchet and pawl unit.
New Technique
When I tested the Mack/Northern outfit I was destined once again to experience something entirely new in driving technique. Driver John Blythe of P. and S. Contracts Ltd. gave a convincing demonstration of how it should be done before I attempted the two-handed job of "cog-swapping" which is a must if the best results are to be obtained from the transmission. To change gear in the correct sequence it is necessary to move both the main and splitter levers simultaneously when going through the three Lowest ratios, using high and low ratios with each. John Blythe learned from a Mack demonstrator, who came over to this country with the first vehicles, how to carry out this very difficult exercise and now, after covering 82,000 miles with the two vehicles that he drives, he is absolutely master of the art, making gear changes with bewildering rapidity.
must confess that when I first took the wheel I had no idea which gear was which. However, half an hour's tuition from John put me on the right track and at the end of the second day of the test I was doing reasonably well. apart from the odd embarrassing noises.
A tachometer is fitted to the Mack, and the art of driving the vehicle economically rests with strict adherence to the instructions given to drivers to keep the engine working at between 1,500 and 2,100 r.p.m. whenever possible. To achieve this end the amount of gear changing that must be done is not high. Once the vehicle was rolling I found it necessary to drop only two or three ratios to negotiate main road conditions that would have entailed continual changing with many other vehicles running at 32 tons gross.
Speeds obtainable in the gears proved to be first-low 5 m.p.h., first-high 7, second-low 10. second-high 13, thirdlow. 18, third-high 25, fourth-low 33, fourth-high 43 and fifth-high 55 m.p.h. As fifth-low is almost the same as fourth-high there is no point in using it. so there are nine effective ratios available to the driver. Added to the wide choice of ratios is an extremely light clutch operation, only 32 lb. pressure being needed on the pedal. This, with the ability of the engine to hold on to a selected gear for what seems an endless period, makes driving the Mack fully laden a simple and pleasant task on undulating roads of a rather more severe nature than would be found in many parts of the country.
Unfortunately the test was marred by the fact that when the brake test was carried out, or at least when the attempt was made, the load moved and collapsed the headboard slightly. The thought of 20-odd tons of graphite coming through the cab deterred me from carrying out further brake tests. This was indeed a pity because it certainly looked as though the results were going to be excellent. On the first and only stop made, actual retardation was' 16 ft. sec.'" and a Tapley-meter reading of 70 per cent was recorded. This was from 20 m.p.h. and there was a slight locking of the off-side semi-trailer wheels and the tractiveunit rear-bogie wheels.
Improved Headboards Needed It must be emphasized that this, outfit had been taken straight off a trunk service and had not been prepared specially for the tests, Small discrepancies in the brake balance can therefore be excused. It is alarming to think that although the headboard on this semi-trailer was, like the rest of the unit, Very heavily constructed, it could not withstand the pressure of the moving cargo when making a 0.5g stop from 20 m.p.h. It suggests that without a considerable amount of research into improving headboard design in general, regulations for better braking and higher capacity vehicles are going to do little to improve the safety factor for the driver in the event of a head-on collision, or even during an emergency stop.
Throughout the whole test the braking system gave the impression that it was completely up to its task, and 1 particularly liked the handbrake control which, although situated some distance away from the driver, was so easy to apply that comparison with anything else I have used is simply impossible. One thing I did not like about the vehicle was a feeling that the steering was not quite positive, it did in fact need to be "sawn at" somewhat to keep a straight course. 1 first thought when driving the outfit loaded that the cause was a dry fifth-wheel; but when the semi-trailer was changed on the second day to allow the empty fuel consumption tests to be carried out the problem was still there although the coupling was found to be well greased.
For the hill-climb test a section with a grand,. Scottishsounding name was used—Hangman's Bray. This has a maximum gradient of 1 in 7 and an average gradient of 1 in 10. Although only one-fifth of a mile long, this section includes the steepest part of the climb right on a tight left-hand, right-angle turn—presenting an extremely severe test for a machine with two tandem-axle bogies. Climbing from bottom to top in 51 sec. the lowest gear needed was first-high and this was engaged for 23.2 sec. The lowest speed recorded was in fact the maximum obtainable in that gear, 7 m.p.h. With an ambient temperature of 10°C (50°F) the engine coolant was 76`C (170°F) at the start of the climb and when checked at the end this had not altered at all.
To the radiator shell of the Mack is fitted a thermostatically controlled shutter, and it was significant that thisonly opened on rare 'occasions, such as at the very top of the hilt-climb, for about the last 20 seconds, Driver Blythe told me that all through last winter most of the night trunk runs were completed without the shutters opening at all, the resulting comfort in the cab, through the coolant temperature being kept high in the heater, was such that the dress of the night was shirt-sleeve order.
Consumption Constant
Fuel consumption figures shown in the performance panel are low by British standards but are constant under varying conditions. The same can be said for the average speeds, which also remain fairly constant. The big advantage claimed by the operator is the complete reliability of the machine and the fact that his drivers are able to complete a 400-mile stint every night for five nights a week almost irrespective of the conditions.
Bad visibility might be thought by some to be an inherent fault with a bonneted type of machine such as the Mack but, in fact, the visibility from the driving seat is extremely good. Taking the sight line at the centre of the bumper bar, the road can be seen at 26 ft. Over the wings, however, it is about 10 ft.—depending on the stature of the driver. The only snag I found with the vehicle was the lack of width in the cab. This makes manceuvring backwards in close quarters a little difficult, because the front of the trailer very soon obscures the vision of the driver when reversing on the blind side. To offset this, the superb West Coast-type mirrors give a completely' unobstructed view of the nearside of the outfit and I would think that once used to the sluggishness of the tractive' unit's starting to-turn •--this is entirely due to the length of the wheelbase--a driver would find little difficulty in handling it with complete ease.
At £10,500 each the outfits are expensive, but this again_ is slowly but very surely being offset by the complete reliability in service.