Moulton attempted to replicate the hydropneumatic suspension of the Citroën DS in a cheaper format. The aim was to provide decent ride quality in a small, lightweight vehicle - an ongoing challenge for automakers.
The system replaces the separate springs and dampers of a conventional suspension system with integrated, space efficient, fluid filled, displacer units, which are interconnected between the front and rear wheels on each side of the vehicle.
Each displacer unit contains a rubber spring, and damping is achieved by the displaced fluid passing through rubber valves. The displaced fluid passes to the displacer of the paired wheel, thus providing a dynamic interaction between front and rear wheels.
The system was not popular with home mechanics, as it had to be re-pressurized after a chassis or subframe replacement. Even welding the sub-frame to repair rust damage typically required the system to be drained. The only way to re-pressurize was to pay a properly equipped mechanic, usually at a BMC dealer. Inevitably the charge for this service was higher than many cared to pay.
Cars using the Hydrolastic suspension system:
The Hydragas system was a development of this system.