-----------------------------------------
Hi, Dennis,
Is there a pressure-retention valve in the Jeep's master cylinder? If so,
this valve will hold a small amount of pressure in the system for quite a
while, keeping the wheel cylinder seals tight, but after a number of days,
weeks, or months, the pressure will eventually dissipate, often allowing a
gradual seepage past the wheel cylinder seals. I don't know if your Jeep's
system uses this valve or not, but it might be a factor. Even if the system
does not use this valve, any system that sits for a long time will tend to
develop a little bit of seepage as the seals retract a tiny bit from disuse.
This is true even if the wheel cylinders have cup expanders.
Also, a further comment on my earlier posting: Silicone brake fluid can also
leak almost undetectably, although I've heard that its evaporation rate is
slower than standard brake fluid. If this is true, it seems that a small
silicone fluid leak would build up enough fluid to form a drip more easily
than standard glycol fluid. However, I've never personally compared the
evaporation rates of the two fluid types, so I'm not going to push that
issue. Maybe someone has actually experimented with the two evaporation
rates?
Now, just a note about converting back from silicone DOT 5 fluid to DOT 3,
4, or 5.1:
I notice that you said you refilled the Jeep's system with DOT 3 fluid to
replace the silicone fluid. While I haven't personally heard about any
negative experiences from converting back to glycol-based fluids (assuming
that the system is flushed with the glycol fluid), I happened to read
something on the Internet recently that "might" suggest a possible problem.
The article has some interesting comments and can be found at:
http://www.ll.net/XS-XJ/tips/maint1.htm
However, I wouldn't automatically take the entire article at face value,
because I did notice some glitches. For example, the author says that if you
are using silicone brake fluid, you should "crack the bleeder screws before
each racing session to make sure there is no water in the calipers." Well, I
don't think it would do a lot of good with silicone fluid, since the water
would collect at the BOTTOM of the cylinders and the bleeder screw is at the
TOP of the cylinder, where it is supposed to allow air to be purged, not
water. Maybe a very vigorous, higher-pressure bleeding would slosh the water
around enough to get most of it out, but the only way to get all of the
water out would be to remove the pistons from the wheel cylinders. The
lesson here is NEVER let any water get into a silicone-fluid system.
The author did make a good point about corrosion inhibitors in DOT 3 and 4
(and 5.1?) fluids being able to handle typical corrosion problems, and how
these corrosion inhibitors would eventually break down, requiring occasional
fluid changes. I suspect (but not sure) that these inhibitors are similar
chemically to anti-freeze corrosion inhibitors, and to keep anti-freeze
corrosion inhibitors alive you have to occasionally change the anti-freeze,
even if the specific gravity reading says it's still OK.
Carry on, folks,
Alan
(Salt Lake City, Utah)
===
To unsubscribe from the mil-veh mailing list, send the single word
UNSUBSCRIBE in the body of a message to <mil-veh-request@skylee.com>.