types of brake fluid

M

Marty & Caryl

Guest
I found this write up while reviewing brake fluid. I thought it was
interesting, you may too:

The U.S. Department of Transportation issues specifications for brake
fluid. The three main types of brake fluid now available are DOT3,
DOT4 and DOT5. DOT3 and DOT4 are glycol-based fluids, and DOT5 is
silicon-based. The main difference is that DOT3 and DOT4 absorb
water, while DOT5 doesn't.
One of the important characteristics of brake fluid is its boiling
point. Hydraulic systems rely on an incompressible fluid to transmit
force. Liquids are generally incompressible while gases are
compressible. If the brake fluid boils (becomes a gas), it will lose
most of its ability to transmit force. This may partially or
completely disable the brakes. To make matters worse, the only time
you are likely to boil your brake fluid is during a period of
prolonged braking, such a drive down a mountain -- certainly not the
best time for brake failure!

As a DOT3 or DOT4 brake fluid absorbs water, its boiling point
decreases. It can absorb water from the air, which is why you should
avoid opening your car's brake fluid reservoir. For the same reason,
you should always keep containers of brake fluid tightly sealed.

DOT5 fluid does not absorb water. This means the boiling point will
remain relatively stable, but it also means that any water that does
get into your brake system will tend to form pure water pockets,
which could cause brake corrosion.

Two other important things about brake fluid: DOT3 and DOT4 eat
paint, so don't spill it on your car. Also, none of the different
types of brake fluid should be mixed. They can react badly with each
other and corrode your brake system.

So with the Amphicar, which will be better? Would we want water in
my brake fluid or pockets of water in the system?
Marty in WI
 
A

a_colo_native

Guest
Marty,

I am using DOT 5 myself. I decided to go that way because I swim my
car at least once a week and quite often more than that (75+ hours
since March). I spoke with a local guy who does million $
restorations specializing in Bugatti (he has 3 of J. Lenos there
now). He reccomended DOT 5 because of the amount of time in the water.

Basically it boils (pardon the pun) down to a personal preferance.
DOT 3 or 4 will give a firmer pedal than DOT 5 does. I will be
flushing my system next Spring and disassembling the cylinders to see
what it looks like inside. I wanted to do an experiment with the DOT
5 to see the outcome. I.E. How much water is in the system, corrosion
and any other observations.

So, go with your personal preferances. Just be carefull not to mix
them!

John "DOT" Bevins
 
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