[Off topic] ABS & synthetic brake fluid

[Greg Hermann]

> I work with DOT 5 often when doing restorations etc. It works very well, in
>particular in vehicles which see limited driving time or severe braking. I
>have never noticed a problem with loss of pressure or a spongy feel either
>unless there was air in the system. Last I heard you can't compress a liquid
>unless it has exceeded it's boiling point and is in a gaseous state.
>
>DOT 5 better known as Silicone fluid is not hydroscopic at all. This is why
>many people use it in their antiques. It doesn't cause the wheel cylinders
>and the master cylinder to corrode. It is recomended you flush the system.
>It also works better if you rebuild the cylinders and nearly polish the seal
>areas as it tends to leak easier than DOT 3 or 4 fluid.
>
>It is very hard to keep it from aerating. This is why it is not recommended
>for ABS systems. When bleeding the system you should not "pump" the brake
>pedal. Either bleed by using a pressure bleeder or by pushing the pedal to
>the floor once, releasing the pressure at the cylinder, slowly allow pedal
>to return, then repeat until all the air has been removed. Very time
>consuming. Once all the air has been remove check levels often. If the fluid
>becomes aerated it is very hard to remove the air.

While it is true that a DOT-5 fluid is not hygroscopic, that does not stop
moisture from finding its way into a brake system (when it breathes with
changing temperature, just like with a fuel tank, among other things.)

Because the fluid is not hygroscopic, the water that does get into the
system collects in pockets in the system over time--causing localized
corrosion, and--in cold weather--causing the possibility of freezing and
maybe plugging part of the system with ice. Also--when the brakes are used
hard--causing the possibility of boiling if the water is at a hot spot.

So--it is NOT wise to use DOT-5 fluid in a street vehicle unless you flush
the brake fluid out every six months or year. A DOT 4.5 (a high temp 4) is
a better deal for street vehicles. You still need to flush it annually to
keep the boiling point up, since 4.5's ARE hygroscopic.

Regards, Greg
>
>Scott