4-208. BRAKE SYSTEM SERVICE. (Continued)
a. Bench Bleeding.
The purpose of bench bleeding is
to remove the air from the mater
cylinder so when it is installed on
the vehicle, the brake system
bleeding will be reduced.
(1) Plug the outlet ports and mount the
master cylinder (1) in a vise with the front
end tilted slightly down.
(2) Fill the reservoir (2) with clean brake fluid
(Appendix D, Item 4).
(3) Using a smooth, rounded end tool, stroke
the primary piston about 1 inch (25 mm)
several times. As air is bled from the
master cylinder, with the outlets plugged,
the resistance to the primary piston travel
will not allow the full 1 inch (25 mm)
(4) Reposition the master cylinder in the vise
with the front end of the master cylinder
tilted slightly up.
Again, stroke the
primary piston about 1 inch (25 mm)
(5) Reposition the master cylinder in the vise
to the level position. Loosen the plugs
one at a time and push the piston into the
bore to force the air from the cylinder. To
(6) Fill the reservoir and install the master
prevent air from being sucked back into
cylinder to the vehicle.
the cylinder, tighten the plug (s) before
allowing the piston to return to its' original
Use extreme care to prevent brake
fluid from contacting any painted
b. Manual Bleeding.
If the vehicle is equipped with power brakes,
deplete the vacuum reserve by applying the
brakes several times with the engine off.