In 1962 BMC sprang a surprise with the 1100 – in one area in particular.
Even without its innovative interconnected hydrolastic suspension, the BMC 1100’s status in the automotive pantheon would have been beyond question. However, a good deal of its historical significance remains bound up with its adoption. While interconnected suspension designs were not an entirely unknown quantity by the late Fifties, it was the first production application of a fluid-based system in a compact, affordable (and no small matter this) British car.
The use of rubber (to say nothing of fluid) as a suspension medium was not something that Alec Issigonis seemed to favour at first, but he became convinced after sampling a Morris Minor which had been re-engineered with a prototype rubber suspension. Having discerned its potential, Issigonis, in conjunction with Alex Moulton developed an interconnected design employing rubber springs for the the stillborn Alvis TA/350 project, initiated in 1952. After this programme foundered and Alec was lured back to Longbridge, a good deal of this technical carry-over travelled back with him, along with several of his team.
Serious development of what was to become hydrolastic progressed from this point, with a series of Morris Minor mules running versions of the Moulton interconnected rubber/fluid suspension design. And while hydrolastic had been considered for both ADO 15 and 16, it was the larger car that was deemed best to pioneer it. Not that it was foremost in Issigonis’ thinking at first; conventional springs were also briefly considered, a matter which lends credence to what some have observed as a longstanding distaste on Alec’s part towards independent rear suspension.
In a 1962 Motor interview which coincided with the 1100’s introduction, Issigonis was asked by the journal’s technical editor why he had chosen an independent rear suspension over a more normative beam axle. Alec’s reply was interesting. “We did consider using a rigid axle, but in the end just didn’t. There were practical considerations, and it did not make such an elegant little unit.” He did however also let slip the following, which was perhaps more telling, stating, “You can only use this interconnected system with all independent springing.”
Hydrolastic saw conventional steel springs and telescopic dampers replaced by displacer units at each wheel, interconnected fore and aft. The displacer units were separated into two chambers by a reinforced rubber diaphragm, filled with a mixture of 49% water, 49% methyl-alcohol, with 1% each of a corrosion inhibitor and a mandatory dye. The upper chamber contained a conical rubber spring, while the lower chamber housed a tapered piston, engaged by the action of the upper suspension arm.
As road shocks acted upon the front wheels, upward forces would push against the tapered piston in the lower chamber, displacing fluid through a valve in the diaphragm into the upper chamber where hydraulic pressure would actuate the rubber spring. Fluid would then be displaced through the interconnection tube to the adjacent rear displacer, with hydraulic pressure acting upon the rear piston, forcing the rear wheel downwards, thus allowing the body to remain level, irrespective of road conditions.
In its ADO 16 application, the mechanical and hydraulic layout was carefully designed to allow the rate of displacement to vary according to speed and load, providing an element of progressive rate springing. Furthermore, owing to these progressive effects, in conjunction with the variable flow through the connecting pipes, pitch and bounce were minimised, while cornering forces caused the opposed side displacers to act against downward forces, reducing the tendency to roll. Further aiding road behaviour was the fitment of twin anti-pitch torsion bars anchored to the rear trailing arms and rear subframe. Additionally, a conventional rear anti-roll bar was also fitted, to balance the front-rear roll couple and limit excess understeer.
BMC’s new Technical Director outlined the 1100’s hydrolastic principles thus: “Our suspension is much stiffer [than Citroën’s], and though we don’t make any great claims for it being super comfortable, our compromise has let us put what we think is a very good system into a cheap car. We were not trying to build a DS 19; this car is a compromise“.
In their August 1962 test report, Autocar were lavish in their praise for the 1100’s hydrolastic set up. While they found that the car was not entirely free from pitch effects on undulating surfaces, they reported that on really poor roads, like pavé for instance, that not only its ride comfort, but the car’s controllability in such conditions was “extraordinary“. The test team also noted that the “extremely small degree of roll during fast cornering” was “almost uncanny“.
Autocar’s summation of the car’s dynamics deserves quotation in full. “On its behaviour, conclusive opinions have been formed; the unanimous view of the test staff is that for overall rating for ride comfort on smooth or rough roads at all speeds, controllability in these conditions, adhesion in the wet or dry, inherent safety and steering response, there is no better car, irrespective of size“.
There can be little doubt that the 1100 was not only something of a revelation in 1962; there being little to compare it to at the time, but also a car which gave not just rival carmakers, but those in the luxury sector something of a sharp intake of breath. But there was a rather sizeable elephant in the back seat and that was cost. According to Autocar, BMC were charging approximately an extra £137 (in 1962 money), model for model for an 1100 against that of a Mini – itself one of the cheapest cars on the market. The cost of this level of sophistication therefore appears (on face value at least) to have been borne almost entirely by the manufacturer.
One therefore might argue that a similar result could have been achieved with conventional springs and dampers; Peugeot illustrated what could be done three years later with the similarly sized 204 model, a car very much in the ADO 16 idiom. Fiat got there even more inexpensively in 1968 with the simply clever 128. It would not be until the early 1970s that anyone returned to a more cerebral approach.
Because for all its merits, hydrolastic proved something of a flawed premise, let down by in-service issues, load-related problems a self-levelling addition might have addressed and a lack of quality control in manufacturing and at BMC/BLMC agencies. Hydrolastic could therefore be seen as Issigonis in microcosm. On one hand it illustrated the breadth of his engineering principles, his high-minded conviction in providing the driver with the absolute most in terms of active safety, dynamic capability and living space, but also his disregard towards the economics of the business.
Are we therefore suggesting that hydrolastic may not have been the right choice for ADO 16? That remains a matter of debate. The 1100 would have been a success without it, of that we can be fairly certain. But whether it would have been as significant a motor car is another question entirely.
 “Rubber is always too stiff”, Issigonis wrote during the early 1950s.
 This experimental Minor was the brainchild of Jack Daniels, then head of R&D at Cowley. Daniels enlisted Alex Moulton to work on this project entirely without Issigonis’ knowledge or input. Given this, it’s a wonder he accepted it at all. Daniels was later to work closely with Alec on the Mini, following the latter’s return to BMC.
 Hydrolastic was initially not deemed appropriate for the Mini, Alex Moulton later saying it simply didn’t work on the smaller car. In the August 1962 Motor interview, Issigonis poured cold water on the notion that it would be incorporated, when in fact this did take place in 1964. However it proved to be both ineffectual and costly, and by the decade’s end the Mini (although not immediately the Clubman) reverted to the cheaper and more effective rubber cones.
 Alec stated in his notebooks that he only adopted IRS for the Alvis prototype with reluctance, when he realised that the interconnected suspension design could not work with a rigid axle.
 Issigonis: “We do not feel we have put the emphasis on comfort; we have erred on the side of making the car safe, making it swervable in an emergency.” (Motor, August 1962)
 The 1970 Citroën GS (and to some extent, the 1971 Alfasud) were perhaps ADO16’s spiritual successors.
Sources and quotes. See part one.