Brake Fluid

[CSS-Registry]

ok y'all,

i have completed the brake system on my truck and wanted some of your thoughts on which brake fluid to use.

the system is almost all new - new lines, new wheel cylinders, new calipers and a rebuild master cylinder. the only thing that is not new is the proportioning valve that i pirated of an 80s Dodge Ram with front disc and rear drum.

any opinions on what sort of fluid to use? am i limited to DOT 3 since i am using the old proportioning valve? is DOT 5 a safe alternative? if so, why?

Ben

[Blue67]

Ben, I did a search but didn't find it. Saw a post on this somewhere a couple months ago. Maybe Norm's forum.
As I remember it it is OK to use DOT 3 or 4. If you switch to DOT 5 and there is ANY 3 or 4 left in the system you'll have big problems
Blue

Edit: Found it here. http://www.t137.com/DTAarchives/8Apr06/ ... 15591.html

[nfury8]

You will find all kinds of info pointing one way or the other on this.
You aren't limited by the valve, just flush it with alcohol.

A super quick run down:

DOT 3 is glycol based- like antifreeze, will absorb water, eats paint, is cheap,
can be bought anywhere, is easy to bleed, and boils at 400 degrees.

DOT 5 is silicone, doesn't absorb water, allows water to pool in the cylinders instead,
is safe on paint, can be hard to find, is considerably more expensive, is hard to bleed
because it traps microscopic air bubbles, if not bleed completely can cause a very
mushy peddle, and boils at 500 degrees.

Very few manufacturers spec DOT 5, it isn't the magic item it seems. I was just reading
the other day that the military was the primary user of DOT 5, and that they are actually
looking to switch back.

DOT 4 or DOT 5.1 seem to be the way to go. Both have improved boil protection (450 and 500),
and are compatible with DOT 3. Locally I have seen DOT 4 for nearly the same price as DOT 3.

No mater which fluid you use, it should be regularly bleed and replaced, whether it acts like
it needs it or not. The glycol based fluids need flushed to remove absorbed water and the
silicone needs it to remove water deposits. It is generally recommended that brake fluid
be flushed and replaced about as often as you change antifreeze, every 1 to 2 years.
This is an often overlooked maintenance item, that can not only cause rust and poor
performance, it can also lead to catastrophic failure.


As Blue mentions, the system must be completely free of all the glycol based fluid before using silicone.
If you have ever tried to clean up silicone, you know it is hard to clean off. As such, once you switch
to silicone based fluid, there is no going back; short of replacing most of the system.

[Cageman]

I remember seeing on some TV show they were using purple colored brake fluid, I was always curious as to what brand it was, and what DOT rating it is. I just did some research, and dot5 is purple or blue. They wont mix, you're right. A way to check what you have is take a sample out and add water, shake it and the dot3 and 4 will mix right up with water and stay that way, dot 5 will seperate. Simple test huh. Same thing with dot 5 and 3, 4. Mix them together and they will seperate like lyaers, then you know you have the wrong stuff if your trying to add. Simple too.
I would say dot 3 or 4 is fine.

[pismopowerwagon]

Dot 4 is the way to go for sure .