Brake Bleeding

FEBRUARY 1, 1948
The following procedure may be used as an alternate method in bleeding the brakes on the D18 series.  This procedure may offer some improvements over the procedure outlined on Page 52 and 53 of the D18S & D18C Maintenance Manual.
Disconnect the brake fluid supply line at the reservoir.  Connect the pressure pot hose to the fluid supply line.
With a strut pump, or hand pump, apply a pressure of 40 pounds per square inch to the pressure pot containing hydraulic brake fluid.
With a receptacle under the brake assembly, open slightly, the lower bleed port, the three cylinder bleed ports, and slightly loosen the hose connections at the top of the shuttle valve.
Turn on the pressure from the pressure pot.
Pump out the copilot’s lines first, and then the pilot’s lines by pumping the brake pedals very slowly eight to ten strokes each.
As soon as all air bubbles have been eliminated at the hose connections to the shuttle valve, tighten the hose connections.  Repeat step 4 if necessary to eliminate any traces of air bubbles at this point.
After tightening hose connections at the shuttle valve, repeat step 5, pump up pilot’s brakes and set parking brake.
Open lower bleed port, and bleed brake through copilot’s brake line.  If fluid will not flow through lower bleed port, tap the shuttle valve slightly with a mallet, or if necessary, loosen the copilot’s hose connection to the shuttle valve.  This should allow the valve to shuttle, permitting fluid to flow through the brake assembly from the  copilot’s line.  Tighten the hose connection, and bleed through the lower bleed port until no air bubbles are visible.
Close the lower bleed port and remove the bleed screw on the top cylinder.  Bleed all air from the top cylinder and replace the bleed screw.  Bleed the center cylinder and lower cylinder in the same manner.  The outer brake housing should be tapped lightly with a mallet during this portion of the bleeding procedure.
Maintain 25 to 40 pounds per square inch air pressure on the pressure pot throughout the bleeding procedure.
If the copilot’s hose connection at the shuttle valve was loosened in step 8, to allow the valve to shuttle, it will be well to again loosen this connection slightly and check for air bubbles at this point.
Check brakes for proper operation.  If brakes are not solid and positive, repeat the bleeding procedure.
If brake are positive and solid, pump up pilot’s brakes, and set parking brake.
Release pressure and disconnect pressure pot line from fluid supply line.  Connect fluid supply line to main reservoir and fill tank to within twon inches of the top.
Release parking brake and check brakes.  If after a few hours brakes feel spongy, pump up pilot’s brakes and set parking brake.  Allow airplane to set for 12 hours with parking brake on.  This will sometimes eliminate spongy brakes.

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