The Citroën DS/ID series automobile was first shown to the public in 1955 and sold until 1975, when production figures reached 1,330,755 (1996, Reynolds/de Lange, p.22). The car utilized a unique suspension and control system based upon hydropneumatic principles. This feature gave the car its singularly comfortable ride, and was a precursor to highly developed systems now used in military vehicles and cars.
Traditional suspension springs were replaced by gas-filled spheres which topped hydraulic cylinders. Damping was provided by way of restrictors between the two, and a system of valves and linkages provided automatic and manual control of the ride height. Major components of the system included the pump, the regulator and the reservoir. These, along with related parts, were painted black. Besides the suspension, the system was used to enable power assisted steering, braking, and transmission declutching and shifting on various models.
Until 1964, all cars used a castor-based hydraulic fluid in this system that was red in color called CH12, when it was supplanted by synthetic LHS2 (Reynolds, p.22). In 1966, the use of LHS2 began to be phased out in favor of a mineral base fluid that was green in color. The older, LHS2 fluid cars used seals and other parts that were incompatible to the new LHM, and thus could not utilize the advantages of the new type of fluid. To protect against cross contamination of incompatible fluids, a potential disaster, the component color was changed to green.
Production of LHS2 has dwindled to almost nothing, and in many areas, it is not available at all. It is unknown at this time how many of the early, LHS2 fluid cars survive, but there are enough of them to make it a worthy effort to supply owners with some kind of substitute for unavailable fluids, or to find a blend of liquids that would copy the characteristics of the earlier CH12. As stated earlier, this fluid is known to be castor-based, so it will be easier to copy.
At this time, many owners use DOT 3 brake fluid. This works, but viscosity differences cause numerous system problems such as malfunctions of orifice controlled operations, excessive noise and deteriorated ride and handling. Lack of lubricity has caused excessive wear to critical parts and seals.
I have decided to rediscover the correct ratio to blend castor oil and DOT 3 brake fluid and thus simulate the characteristics of CH12. Trials performed during the summer of 1999 on my own car, a U.S. export specification 1968 ID 19, showed promising results. Cycle times improved as well as the sound level during pump operation. Ride characteristics improved and steering effort decreased as well as its associated noise. Seal leakage diminished considerably. No doubt, the added lubrication was a benefit. But the optimum ratio was not found. Excessive amounts of castor oil led to undesired behavior and cold weather caused more problems, most likely because of elevated viscosity.What was needed was a way to test my mixture for optimum ratio to obtain a viscosity similar to actual LHS.
Copyright 2013 by Mark L. Bardenwerper, Sr. All rights reserved. Last Modified 1/19/13