Steve,
You say, "To my knowledge, opening the wheel bleed valve for "gravity" does
not result in flow, unless you are unlucky to have air entering the system to
allow fluid out the same opening."
Air can't flow into the bleed valves because of the hydrostatic pressure of
the fluid in the higher reservoir.
Gravity bleeding works with Tigers with stock brake line routing and many
other cars that don't have large vertical loops above the master cylinder that
can trap air, or that have low master cylinders.
If there is fluid in the system that has been there enough days for the air
to come out of suspension and the brakes have been applied many times, air will
either gravitate towards the master cylinder where it will escape or to the
wheel brake cylinders where it will be trapped.
Here is the bleeding process. First, check to make sure there is enough fluid
in the master cylinder and loosen the cap so air can easily enter. As you
open a wheel cylinder bleed valve, the air will come out first and then the
fluid
will start flowing. The longer it takes for the fluid to come out, the more
air there was in the cylinder.
I've done this for many years on many vehicles and it has worked, so try it.
It's just a quick easy method that you can do without help or bleeding
equipment.
John
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