| No prob with the hi jack…info is valuable to all..
Silicon based brake fluid has a higher boiling point than that of glycol based fluids (dot 3 and dot 4), but not dot 5.1
Dot 2 – not used any more, but was castor oil based
Dot 3 dot 4 – polyethylene glycol, and mineral oils, esters, ethers based
Dot 5 – silicon based
Dot 5.1 – glycol based…yes that’s right glycol
Glycol based brake fluid is approx 2 times less compressible than the others, so gives a better feel.
Lets remember one important fact regarding braking systems with fluid inside it…you are not compressing the fluid !! you are applying a force at one end of the system, which applies another force at the other end.
The reason brakes feel spongy, is the inclusion of air, which is compressible.
Boiling points are as follows :-
DOT 3 205°C
DOT 4 230°C
DOT 5 260°C
DOT 5.1 270°C
If you are using dot 5 brake fluid and want to remove all the water, you can, but its not easy. The simplest way is to remove all the fluid as best you can, then apply a vacuum pump to the lines and calipers. This lowers the boiling point of the water and turns it into a vapour. This can then be sucked out of the system.
obviously you may encounter probs with pistons being sucked back against their stops, and air being drawn into the system, depending on the mechanical state of your system !
Obviously you don’t see many diy’ers doing this to their bikes as its specialised.
My opinion is to use dot 5.1.
What a lot of people do when they buy a tin of brake fluid is shake it up on their way home..thus mixing the fluid with the vapour in the space above the fluid. They then put this straight into the system and wonder why their brakes are spongy !
Best thing to do is when you get the fluid back home, let it stand overnight and settle, allowing the bubbles to escape.
Last edited by DEMON : 21-Aug-2006 at 18:19. | 
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