Originally Posted By: Trav
Originally Posted By: i_hate_autofraud
I would not gravity bleed, air can get into the bleed fitting as it sits open, instead vacuum
bleed with a hand pump tool made for that. Of course make sure the master cylinder stays at the right level.
And it wont get in using a hand held vacuum pump? Air will not get into the system from opening a bleed screw on a full system.
The trick is to get your flare nut wrench on the bleed screw, then the rubber bleed nipple and vac hose over the
bleed screw and pull vacuum before you open the bleed screw, then close the bleed screw as vacuum drops, pump some
more to create vacuum and open the screw again until you get enough old brake fluid out.
(I'm referring to hand held vacuum pumps for brakes with hoses, nipples and a collection bottle in a kit)
The idea is you always have vacuum applied before you open any bleed screw, therefore no air gets in.
While trying 'gravity bleeding' yrs ago I watched brake fluid drain down a clear hose, but as it ran out
slowly, I noticed air creeping up the hose, the fluid does not block the air all the way up the hose,
it moves to side and lets air pass.
That's why I don't do gravity bleed, if you want old fluid out, either vacuum or use pressure with a
pal stepping on the brake pedal while you work the bleed screws.