[dv8zen]

I have questions regarding bleeding brakes that use DOT 4 and 5.1 fluid, typically with a syringe style bleed kit:

Why does DOT 4 and 5.1 have a shelf life of 1-2 years? If it's only because it absorbs moisture, what should I expect if I decide to "de-gas" old unused DOT fluid through the vacuum method before adding it to a brake system (ex. Avid/SRAM)? Has to be better than what's currently in the brake, right?

If I create a vacuum with the syringe attached, is it like vacuum bleeding in a way (ex. susp vac bleeding)? xD I hear people say it's useless, and it's just air passing by the seals, but more "sciency" guys say boiling points lower in a vacuum and the moisture in the DOT fluid is changing to a gas.

 

[johnbryanpeters]

Pulling a vacuum on a glycol ether brake fluid is not going to remove water. Period.

Vacuum bleeding removes air in the system.

 

[Adventurous]

I mean sure, in theory subjecting the fluid to a vacuum environment would eliminate moisture, but vacuum bleeding isn't introducing a vacuum to that degree. It is just vacuuming, aka pulling, the fluid through the system as opposed to pressure bleeding or pushing it through.

JBP is right, once the fluid absorbs moisture that's the end of things. Might as well just grab a fresh bottle of DOT fluid, flush the entire system, and replace with new fluid.

 

[Sandwich]

better way to live is to buy very small bottles of dot fluid and then throw them away after a year. You are probably way better off flushing your fluid with new, unopened dot 4 every year than you are with dot 5.1 and going more than a year on a bleed.