lml@lancaironline.net Mailing List Archive

Regarding the bleeding of brakes, the standard method of filling brake systems at automotive factories is to leave all connections tight and pull a vacuum at the reservoir. Then a measured quantity is added to the reservoir, the vacuum released and that's it. One problem with our systems is that the hoses and lines are larger than they need to be, allowing air bubbles to stay in place and not be "dragged along" with the fluid. I think the best approach is to pull a vacuum at the reservoir. It won't "pull debris" from the wheel cylinder, as the fluid there stays put. The bubble enlarges and that gives it the impetus to rise to the reservoir. Or, as Robert says, a pressure bleed can push the fluid fast enough to drag the air with it. Except I would probably pressurize the wheel cylinder to at least push the air uphill. Either way works, though.

Gary Casey

Reverse bleeding pushes all the debris from the wheel cylinder up into the master cylinder. This will be trouble in the future..

The two person method works well but you must not wait long between the pumping action at the master cylinder as any bubble
in a hose will travel beyond the prior pumping action rendering the bleed useless.

The best is the pressure bleed. A small pot is filled with brake fluid and pressurized to 20 psi. The pot is connected to the
master cylinder reservoir. When the bleeder valve is opened at the wheel cylinder, the fluid is pushed out at a fast rate allowing
all debris and air to escape. This is the de-facto standard in the auto industry and commercial aircraft.

Robert