[bobcowan]

I agree with all of the above.

Essentially, the higher the DoT number, the higher the dry boiling point. In racing, brake calipers can get really hot, and boil the fluid. Then it becomes a vapor and is compressable. Then you get a soft pedal.

3 and 4 mix just fine. But if you mix 3/4 and 5, it will clot. Then you get real erratic braking. I'v also heard fluidthatixing them makes them more corrosive, but I'm not really sure about that.

There's a new fluid that came out a couple of years ago, DoT 5.1. It's a glycol based fluid, jsut like 3 and 4. But has the performance charectoristics of 5. I have never used, because I have never been able to find it. I use Wilwood.