Interesting. My car certainly is no "trailer dolly" (22,000+ miles in the
past 3 years), and I've been running silicone brake fluid for the past 2
years with no problems. No unusual fade, no soft pedal (and I DO drive
hard). Admittedly, I was aware of the air entrainment problem, so I was
verrrrry careful.
I've heard about the switch problem from other sources, so I can see a
difficulty there, though the Midget uses a mechanical switch that isn't
exposed to the fluid. Since Midgets don't run a brake booster, (unless you
want to count the occasional adrenaline rush <grin>) abrasive ash isn't a
problem (though I've known a few abrasive ashes in my time...).
If silicone fluid is so touchy/nasty, why does the military specify it
(particularly given the range of extreme conditions they operate in)?
Ditto with racers?
On Tuesday, December 30, 1997 11:55 AM, Heather & Joe Way
[SMTP:sierrasa@psln.com] wrote:
> Chris Kotting wrote:
> >
> > I have seen this conversation before. Some people sing silicone's
praises
> > (myself among them), others relate horror stories. I don't get it.
What's
> > the difference? Any chance we can correlate the finer details (like
who
> > made the caliper seals and/or the brake fluid) and maybe determine
what's
> > causing this difference in experience?
> >
> > Chris Kotting
> ----
> Very good questions, Chris. I get involved in it a lot because of my
> job. There are some old answers, some vague answers and some solid ones.
>
> When silicone fluid first came out, it was pretty pure. Most users had
> Christopher Palmer's experience, and he's right about the cause. Brake
> parts engineers have since the late 1920's counted on glycol's softening
> and expanding effect to increase the size of the rubber 10 to 15
> percent. Early silicones didn't do this. (I wonder if Christopher may
> have gotten some old fluid.) The formula was modified with agents
> intended to duplicate this effect. It took some time to get it
> right--but there are still many knowledgeable people who are convinced
> the silicone fluid does not have the proper effect on the rubber. This
> seems to be mostly related to European brake parts, IME.
>
> There are other, more significant problems w/silicone. It turns into a
> very abrasive ash when it is burned. If it is used in a car with a
> vacuum brake booster, and gets past the booster seals into the engine,
> it can ruin the engine in *very* short order. It
> is not so big a problem with later setups where the booster and master
> are sealed separately--many of them even have drains between the master
> and booster. It gets worse with the treadlevac type cylinders that have
> vacuum against the secondary cup or seal, where the fluid is at ambient
> pressure, and gets really bad in Midland-type boosters and the primary
> master on Jaguars of the late fifties through seventies, where fluid
> under pressure is present on one side of the seal in the reaction port
> and vacuum is on the other side. You sure don't want that stuff getting
> into a Jag V-12!!!
>
> Any water that gets into DOT 5 fluid (and there are *several* ways this
> happens, even though DOT 5 is not hygroscopic) will aggregate into drops
> rather than mixing, and the specific gravity of water is greater than
> the brake fluid. So it tends to settle down into low points. If you get
> a drop of water in a disc brake caliper, and then get the caliper up to
> 212 degrees (not difficult--discs run hot anyway) the water will flash
> to steam and the brakes on the front (or the entire car if a single
> circuit master) are *gone*. Get a drop of water in a small port anywhere
> in the system, experience freezing temperatures and all the brakes
> beyond that point are *gone*. I believe this is the main reason OEMs do
> not use silicone--a simple liability question.
>
> Dot 5 fluid is often associated with a low and/or spongy brake pedal.
> The pedal problem arises because DOT 5 tends to entrain air in
> microscopic bubbles throughout the fluid. The labels on the fluid warn
> against shaking and overly vigorous bench bleeding because of this
> characteristic. Since the air does not aggregate, it can't be bled out,
> and it often causes a soft pedal. Most of my customers who have switched
> back to DOT 3 say this is the reason. And when I set up at the Reno
> (Nevada) Swap Meet, I always get several people from sea level asking if
> I know why they have lost most of their pedal--the pedal goes almost to
> the floor. I ask if they have silicone fluid, and guess what the answer
> is. The ambient air pressure at Reno's elevation is enough less than at
> sea level that the air in the fluid expands, making the pedal problem
> even worse. One person I have communicated with on this subject says he
> knows many who have undertaken Pikes Peak tours who have lost their
> brakes 2/3rds of the way up and had to be towed down!
>
> Other points about DOT 5--to the best of my knowledge, *NO* OEM has ever
> put DOT 5 fluid in a standard production car at the factory. This is a
> very telling argument for me. Manufacturers of even the most expensive
> cars, to whom price would be no object, install and specify DOT 3 or DOT
> 4. If anyone knows otherwise, I would appreciate hearing about the make,
> model and year. (I'm aware that some fleet purchasers such as the
> military and the USPS have been known to specify DOT 5 in the bidding
> documents, but these are not standard production vehicles.) It is
> corrosive to electrical contacts, as in brake light switches--German
> cars seem to suffer most from switch failure. Again to the best of my
> knowledge, *ALL* makers of ABS specifically prohibit the use of DOT 5.
> Most of the fleet managers I do work for who had converted their fleets
> to DOT 5 have converted them back to glycol, and most of the
> professional restorers I do work for recommend against it--including, as
> Christopher mentioned, Norman and David Nock of British Car Specialists,
> who are two of the most knowledgeable Brit car people on the West coast.
>
> In a show car, that is driven little or not at all, it makes a lot of
> sense. But IMO any car used regularly enough to be called a "driver"
> should have glycol fluid. BTW, whether the cylinder has been sleeved has
> no bearing on this. A properly sleeved cylinder will not leak air at
> brake pressures, much less silicone. A sleever who tells you not to use
> DOT 5 because it might leak around the sleeve is telling you that he
> didn't put the sleeve in properly. Most sleevers do recommend against
> the use of DOT 5, but it is for the reasons above and their
> recommendation applies to all systems, sleeved or not.
>
> Joe
> --
> ==brake cylinders sleeved with brass==
> ==One-Wire conversions and rebuild
> kits for GM alternators 1963-85==
> ==Quincy, CA==
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