The AD067
The Issigonis space-saving concept of a transverse engine and front-wheel drive was, by the time the Allegro was released, almost 14 years old and had been widely adopted by other manufacturers. In the Austin Allegro line the pioneers of the layout set about creating a modern interpretation, backed by their unequalled experience with the Mini, 1100/1300 (Austin America), Maxi and 1800/2200 models.
Mechanically the
British Leyland engineers showed off their originality and enterprise. The Allegro, or AD067, was the successor to the 1100/1300 (ADO 16) line although at when the car was launched British Leyland insisted it will augment, not supplant, any existing models. It was 6 in. longer, 3 in. wider and 3/4 in. higher than the ADO 16, and its most important technical novelty was the Hydragas interconnected suspension.
Improvements to the Hydrolastic Suspension
Designed, like the previous Hydrolastic system, by Moulton Developments and manufactured exclusively for Leyland by Dunlop, the Hydrolastic suspension had many similarities; but instead of the thick rubber cheeses, pressurized inert nitrogen in a sealed-for-life bag was used as the springing-cum-damping medium.
The then new suspension was much softer than the old, nitrogen gas permitting a more sophisticated approach to the non-return valves and pressure release devices which fed the impulses from wheel movement to the lines of water-based fluid interconnecting front and rear suspension. The whole system was hermetically sealed and designed to last the life of the car without maintenance. No anti-roll bars were used.
At the front end the Hydragas units were mounted vertically above the top A-arms, as on a MacPherson-strut system; at the rear they were disposed horizontally and actuated by bellcranks from trailing arms. Thus positioned, they did not intrude on seating or luggage space. Each Hydragas unit was a nitrogen-filled spherical chamber welded onto the top of a displacer chamber. Between the two chambers were carefully shaped holes covered by rubber compression blocks to control the flow of fluid between the upper and lower chamber.
The resultant 2-way valve provided the required suspension damping. The displacer chamber was hermetically sealed at its lower end by a load-bearing, nylon-reinforced rubber diaphragm which rolled between the skirt and the piston in response to wheel movement. Within the upper chamber was a butyl separator, and the volume above the separator was charged with nitrogen at 250 psi at the time of manufacture. The gas provided the springing. During the fluid-charging procedure 2.5 Imperial pints of fluid filled the space between the separator and the rubber diaphragm.
When the fluid reached the nitrogen charging pressure, it compressed the gas and lifted the separator off the bottom of the sphere. There was negligible stiffness in the separator, so the pressure in the gas would then be the same as that in the fluid, which increased until the car was trimmed to a fixed height in an unladen condition at about 330 psi. The rubber compression valve block within the Hydragas unit provided the necessary bounce damping; there were no sliding seals, thus no friction and no wear. The large quantity of water-based fluid which circulated avoided excessive heat build-up, thus maintaining constancy of damping under arduous conditions. At low deflection speeds the flow in the rebound (down) direction was through the main bleed orifice. In the bump (up) direction, the fluid flowed through the bump bleeds by lifting the small rubber flaps on the side of the compression block, as well as through the main bleed orifice.
At higher deflection speeds the fluid also flowed through the main ports but also progressively lifted the rubber compression blocks. The housings surrounding the blocks controlled the amount of pre-compression that was applied to the rubber, hence the flow characteristics, hence the shock damping. Pitch damping occurred in the front-rear interconnection pipe system. The interconnection pipe was connected to the displacer (lower chamber) underneath the bounce damper. This allows completely separate and optimum damping in pitch and bounce. The old Hydrolastic system had the i/c pipe connected to the chamber above the bounce valve, and thus damping could only be that in the i/c pipe plus bounce damping.
The Hydragas system operated with a leverage of between 4 and 5 to 1 to reduce the size of the units. The cross-tube rear suspension was designed to contain these high "levered loads" so that only forces of wheel-load magnitude were fed into the body structure. It was rubber-mounted at its ends, to a compliant subframe of extreme simplicity. The extent of softening the wheel rate in the pitch mode was constrained by consideration of trim change with load, which was limited by the torsional rate of dual concentric bonded rubber bushes in the rear arm. These were free when the wheel was in the full bump position, but in the normal position they provided a false load at each wheel of 81 lb pulling the body down. This false load reduced the percentage increase of load at the rear when the car was loaded with passengers and luggage and had the effect of reducing the attitude change. The wind-up torque from the dual concentric bushes was transmitted through serrations on their inner sleeves to the shroud.
The controversial side-mounted radiator of the Mini and 1100/1300 was replaced on the AD067 by a front-mounted unit, assisted by a thermostatically controlled electric fan. Apart from receiving full forward airflow, secondary advantages were that the radiator protected the engine from water and dirt – anyone who has ever owned an early Mini or 1100 needs no reminding of these problems - and that removal of the radiator from the wheel-arch duct brought an unexpected but welcome improvement to the interior acoustics. The AD067 was significantly quieter at high speeds than its forebears.
The Allegro was offered with two basic engine options in four displacement sizes and 12 models in all with 2- and 4-door variants of differing trim and equipment. The lesser-powered 1100s and 1300s used the rugged old-timer of a power unit, the pushrod ohv A-series, with a 4-speed gearbox; the bigger-engined Allegros used the ohc E-series Maxi unit in 1500 and 1750 forms with the Maxi 5-speed gearbox, which when the car was released had been revised with an improved rod shift linkage.
The AP automatic transmission was an optional extra on all models except the 1100s. There were three basic grille treatments; one plain, one toothy and one waffley. Braking was by Girling discs at the front and drums at the rear, with a vacuum servo standard on the 1500 and 1750 variants and optional on the others. All Allegros ran on tubeless radial tires, the pushrod engined having 145-13s and ohc models 155- 13s. Performance ranged from a 79-mph maximum and 0-60 mph in 22.0 sees for the 1100, to 95 mph and 0-60 mph in 14.5 sees for the 150 Sport Special. Austin employed a single tuned SU swing-needle carburetor and overrun throttle valve which jointly limited carbon monoxide and hydrocarbons without big power loss.
Inside the Allegro
Inside the Allegro, the first feature meeting the eye was undoubtedly what Austin called a Quartic steering wheel, which was neither a circle nor a square, but midway between - much like an Indianapolis with equal-length straights. Aesthetically it looked odd, but Austin claimed practical advantages like more lap room, etc. Sir Alec Issigonis never lived down his famous remark, made light-heartedly but misinterpreted, that a driver should be slightly uncomfortable to remain alert. It could be argued that this applied to the Mini and to a lesser extent the 1100/1300s, but for the Allegro there was a more relaxed driving position, aided by a notably long margin of adjustment for the seat.
The trunk gave 40% more space than that of the 1100/1300, although it was at the cost of rear-seat legroom. Yet the general standard of comfort in the Allegro remained high. The body shape could hardly be improved; it was both attractive and logical, being a product of British Leyland’s then latest programmed design techniques.
The frontal structure met the EEC's rigorous impact and crush regulations; the metal shell was electro-phoretic paint-treated. A manufacturing novelty was the use of a Fabrostrip main wiring harness, wherein cables were bonded to and laid flat against a base material, simplifying assembly and servicing. For especially wintry conditions, as in Scandinavia, a ballasted coil and heavy-duty battery were fitted. Accessibility of the engine was a great improvement on earlier models, and certainly over some rival transverse-engined cars.
The Worst Car in Britain
Despite the potential of the Allegro, things didn't go well. The execution of an otherwise good design was negated by shoddy build quality. In 1979 it was the fifth best selling car in the UK, but that was the peak, and it went very quickly downhill from there. So poor was the construction and reliability of the Allegro that it was soon dubbed the "All-aggro". In a survey of 4,000 motorists, carried out by internet magazine iMotormag, nearly a quarter - 24 per cent - labelled the Allegro as the car they would least like to be seen driving. It was closely followed by the Morris Ital, which received 23.4 per cent of the vote.
The rest of the top 10 worst cars were: Talbot Sunbeam with 11.4 per cent, Austin Princess with 10.7 per cent, Hillman Imp with 10.6 per cent, Rover 200 with 5.7 per cent, Triumph Acclaim with 4.4 per cent, Rover 800 with 3.8 per cent, Morris 1800 with 2.6 per cent and the Triumph TR7 with two per cent. Was the Allegro as bad as everyone remembers? You can cast your vote below.
