Brake Bleeding Procedure
First, check to ensure that there is no air in they system. Air can be trapped in any high spot in the line and often cannot be “pumped” out. Ensure no high spots during bleeding. The following bleeding procedure may be used:
- Open brake bleeder valve slightly on the brake caliper to facilitate bleeding of air from the system.
- Attach a tube from the nozzle of a squirt can or bleeder tank of brake fluid, to the top of the brake bleeder valve. Pump the handle until oil flows bubble free from service hose before attaching.
- Make sure that the master cylinder shaft is fully extended to open up the internal bypass valve.
- Inject brake fluid (Mil-H-5606) or equivalent, into the puck housing and continue injecting until the fluid travels through the system in to the master cylinder.
- Air in the system will be pushed up and out in to the master cylinder ONLY IF the master cylinder cap (if master cylinder has built in reservoir) or remote reservoir, if used, is at the highest point in the system, and there are no loops in the brake lines.
- Fluid should be pushed through the system until it reaches approximately ¼ inch from the top of the master cylinder or remote reservoir.
- Close the brake bleeder valve, and remove the service hose.
- If the brake system is free of air, the brake pedal should feel firm and not spongy. If not, repeat steps 1 through 7 until system is free of trapped air.
- Problematic systems (especially those with local high spots in the hydraulic lines) may be best bled using a vacuum source at the reservoir and hydraulic fluid supply connected to brake bleeder. Drawing hydraulic fluid up through the system often improves the removal of trapped air in local high spots. High spots may be in the caliper, master cylinders, fittings, or park brake valves.
Second check to ensure that your linings have been adequately broken in using a standard break in procedure. Your lining should produce a shiny transfer layer if properly conditioned. The following procedure should be adequate to condition the linings:
- Apply brake pressure for high throttle static run-up. Note RPM at creep if any.
- Perform 2-3 high-speed taxi snubs to generate 300-400 degrees at brake pads and rotor by accelerating the aircraft to 30-40 mph. Remove power and apply firm braking pressure until slowed to 5 mph and release pressure. Do not bring aircraft to a complete stop during the taxi snubs. After accomplishing the snubs, do not drag the brakes. Allow the aircraft to roll as brake free as practicable until back to the tie down area. Avoid stopping the aircraft completely as much as practicable and park with brake pressure off.
- Allow brakes to cool 10-15 minutes.
- Repeat step 1. There should be a noticeable increase in holding torque.
- Repeat steps 1-3 if necessary. Properly conditioned pads and discs will have a uniform, shiny appearance on the surface.
Third ensure that the none of the o-rings has been damaged or is letting fluid out.
Fourth, check to see if you are getting adequate pressure from the master cylinders by attaching a pressure gage to the brake bleeder seat port and applying pressure. Pressure ranges from 450 PSI to 600 PSI are adequate.
Fifth, ensure that both linings are touching the brake disk. If both linings are not touching, check to see if there is adequate travel of the brake plate anchor along the guide tubes. When both linings are now, the brake plate anchor should be between the center line and the housing. See the caliper adjustment drawing for B3 & B4 brakes under Brake Assembly Drawings at www.matcomfg.com for more details on adjustment of those brakes.