Nippy ride in Welsh valleys
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IL THE effort is taken out of riving by the automatic ption now available on Ford series buses — but it still Ives a very nippy arformanee.
That was my impression fter trying out the prototype us on an incredible tortuous us route worked by South Isles Transport.
The company will evaluate re system by operating the rst bus fitted with the Allison -ansmission alongside ianual Ford buses.
I drove for 85km (53 miles) ) assess the transmission erformance — first on the rotorway from Swansea to ort Talbot and then over the )ute the bus will work up the ,fan Valley to Cymmer, lyncorrwg and Blaengwynfi.
It is impossible to use Leytnd Nationals on this route, nd even the shorter Fords, rith better ground clearance, ametimes come to grief on le hairpin bends, as shown by le remnants of "National" Bd paint on some of the )adside obstacles.
The change points between le four gears in the Allison ■ T 543 transmission are infinely variable and controlled y a combination of the vehile road speed and the throttle osition.
The valves operating the ear-shifts are controlled by ydraulic pressure switches nd input taken from the ngine governor. With the arottle closed, this input to he control valves is boosted, o that changes up take place t lower revs than if they relied olely on the governor input.
With the throttle wide open, his extra pressure to the ontroi valves is reduced to lake the changes take place t higher engine speeds, thus iving an infinitely variable ange of points where chdnges ccur.
On the road this system worked extremely well to give changes just where I would have shifted gear myself. With my food flat on the floorboards, acceleration was very impressive up to the maximum speed of 86km/h (54 mph). The change from first to second took place at 22km/ h (14 mph), second to third at 32km/h (20 mph) and into top at 56km/h (35 mph).
Even at full throttle, with a lightly loaded bus, the changes were amazingly smooth. Driving with light pedal pressure changes took place at much lower road speeds and were even smoother.
To give a better match between the Ford low-speed, high torque turbo unit and the Allison AT 540 gearbox, the torque convertor from Allison MT series for heavier vehicles is used. The combined unit is designated the AT 543.
This convertor is stiffer than the one usually fitted to the AT unit and thus contributes to good fuel consumption, For the whole run over motorway • and mountain roads, the near-empty bus tested returned 23.29 litres per 100km (12.1 mpg), which seemed very creditable to me.
One criticism: the placing of the gear-shift control is too tow down on the driver's left. This made me lean well forward to select the hold positions to descend steep hills on the mountain roads. The control itself also felt rather flimsy for the heavy use it will get in bus applications.
The biggest hope of South Wales Transport is that the Allison will cut down labour costs associated with frequent clutch replacements, every 10,000 miles or so on the, manual Fords.
Apart from this fault, the South Wales engineers are very happy with the performance of the Fords on outof-town routes up the valleys, especially the excellent fuel consumption returned by the buses.
But the drivers disliked the six-speed gearboxes fitted to earlier vehicles and were still not too happy with the latter four-speed boxes.
By fitting automatic boxes, South Wales Transport hopes to reduce maintenance costs and at the same time increase staff goodwill. The gearbox is prot-6dtea from abuse by manual downshifts at too high a road speed. In this situation it will not change down until the road speed has dropped to a safe level.
The Allison option is now available for any Ford operator who wants it at a price of £1,311 more than standard manual specification.