[Kevin in NJ]

The correct answer is...

Read the article.

Seems people have lots of ideas of what is correct. Well back in 1966 in Model A News an article was printed that pretty much gives you the answer.

Now my experiences working with shocks with zero play and a slight amount of play. By play I mean the wings to the body. By slight amount of play, just that-the shocks were super tight and very tight. Oh and I had one that was just fairly tight.

I found that Automatic trans fluid is too thin. A huge difference in the amount of resistance between the zero play and very slight play shocks. The fairly tight was fairly loose. None came close to the time required by the Service Bulletins using my guess of a shock tester arm.

I found that hydrualic jack oil to be a bit looser.

So two fluids to strike from the list of possibilities.

A guy at work gave me some motorcycle shock fluid. I would rate it slightly thicker than the ATF and jack oil. No difference.

So after talking to someone they mentioned this above article. So I dug deep into my collection and found the attached article.

I think that should shed some light on what you should be using.

I would like to point out that if your wing has any play in the body without the nut on top then you are likely are going to need thicker fluid.

I would also like to point out the article was 'scanned' using an app on my iPhone. The app is call Genius Scan and it lets you correct for angles if you are not directly over the top of the article and it makes it a PDF. Probably a good app if you want to do a quick scan of something like an old book at a library.