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Those who have or are contemplating changing to silicone brake fluid might find it worthwhile to read an article in the April 2008 issue of "Skinned Knuckles". But if you disagree with the author (Josh Malks), don't take it out on me, I'm just the messenger and my primary Packard has mechanical brakes.

Josh discusses DOT 3, 4, 5 and 5.1 (which isn't a silicone fluid). He does agree that Dot5 might be a good choice for museum cars and those that seldom see any use. He also gives 5 possible issues to consider before use of Dot5 fluid.

(1) It's marked propensity to aerate which prohibits or should prohibit its use in systems with ABS, and which contributes the spongy pedal which some find objectionable and others don't mind or don't notice. (2) Echlin/NAPA's confirmation that hydraulic brake light switches are not made to be compatible with Dot5 which explains the high rate of brake light switch failure, especially the special units on the V8 Packards. (3) The fact that moisture that enters the system (thru the cap vent for example, the same way it enters any brake system), rather than being finely dispersed as in conventional fluids, lays in collected droplets at low points in the system, leading to the possbility of accelerated rust-out on steel lines. (4) There is little support for its use among hydraulic component makers and rebuilders and such component parts may give inconsistent performance. And (5), one that as a chemist never occurred to me before, if it is sucked into your intake manifold from a booster failure, it's thermal decomposition product includes abrasive sand. This is probably a remote concern but the decomposition product of the triethyleneglycol based conventional fluids are carbon, hydrogen and oxygen, probably passing thru some intermediate state of some gummy tiger snot-like materials but at least not abrasive.

Food for thought.

And a final thought. Just as ethylene glycol antifreeze never looses it's freezing point depressing properties, old brake fluid never looses its incompressibility. But the corrosion inhibitors formulated into both have only a transitory existance as they are consumed in doing their tasks. Flushing and replacing both types of fluids should be a regular part of our old car maintenance schedule.

Good points to consider. I do not use silicone in my 56 400. I am also glad that a chemist was able to define the consistency as "tiger snot" Thanks for passing this on.

I never gave any thought about "tiger snot", perhaps we should ask these guys:

Is DOT 5 heavier or lighter than water????

Lighter than water.

Owen: Thanks for posting the information on DOT5 brake fluid. I was thinking about converting my Chevelle over to DOT5 brake fluid. However after reading your post I have changed my mind about doing so. This kind of reminds me of asking my mechanic sometime ago about using synthetic oil that seems to becoming so popular. He stated that as far as he was concerned it was a waste of money.

I really don't know how much of mechanical expert Josh Malks is, but I know that he is a very good automotive writer. He is one the leading experts in the world on Cords. The book I have that he wrote on the Cord 810/812 is an excellent read. Women have you ever read this book, if you haven't good to your local library and see if they have it. Well worth the time to read it.

John F. Shireman

Anyone have a 55-56 MANUAL master cylinder????? I need to know the FULL stroke of the master cylinder and the diameter of the cylinder.