[rotorwrench]

That is a question that I still haven't seen an answer for. Glycerin was the original fluid used by Houdaille but I've never heard of a chemical break down of the product marketed later as "shock fluid". I've heard that mineral oil, castor oil, and glycerin were all used in Ford products and some mention the shape of the filler plug was the indicator of type used.

Houdaille shocks originally used leather as the materiel for the wing shaft seals and glycerin will protect the leather. The glycerin stays about the same viscosity in all normal temperature variations. If a more modern type treated leather or some other mineral resistant seal is used then mineral oil can be used. As to what type or viscosity I don't know. The viscosity of glycerin or castor oil would have to be measured to see. Hopefully a shock rebuilder will add their 2 cents.

I still have occasion to to work on an old Bell 47 helicopter with a stabilizer bar set up now and then and they used the late type Houdaille dampers. They have a little window so you can see the fluid level and Mil-H-5606 hydraulic oil was used in them. We had to disconnect and time the drop on them with a specific weighted object attached to the arm each 100-hour inspection. They have a needle valve adjustment to get the time right.