lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> "Spongy" brakes can be caused by air in the system (either bubbles or dissolved), radial flexing of the lines and hoses or strain in the mechanical linkage or caliper. Before you make any changes to the system, be sure that all the air is out of the system. H-5606 oil can hold quite a bit of air in solution (like carbonated water). To degas the oil I use a salvaged 20 pound freon tank and an air powered vacuum pump I got from Harbor Freight. I pull a partial vacuum in the freon tank then aspirate about a gallon of oil into the tank. I then reconnect the vacuum pump to the tank, pull a vacuum and close the valve. I'll let the tank sit for an hour or so and then SLOWLY open the valve. Just before use I'll use the regulator off of my paint spray gun to put a 10+- PSI charge in the tank (again slowly). I then flip the tank over, bleed the hose and connect it to the brake line I disconnected from the caliper. I use a clear hose connected to the reservoir vent to drain the waste oil into a can. Once everything is set I'll crack the valve at the tank and allow about a cup of oil flush through the system while occasionally pumping the pilot and co-pilot brake petals. My caliper vents are on top so when I reconnect the brake line to the caliper I can then bleed the caliper by cracking the vent and SLOWLY pumping the petal. For you down vent guys, Cleveland has a cute fitting that adapts the vent to a -4JIC male. This technique works every time (for me) and doesn't require a helper. The brake fluid will also degas during high altitude flight. That is why I always pump the brakes on downwind. Aeroquip 303 is a medium pressure hose with a synthetic rubber liner. Its radial modulus (theoretical pressure it would take to double the circumference of the hose) is much lower than the DH hose or even nylaflow. It should be OK to use as long as it is only used where needed (at flexible joints). Use hard line everywhere else. If you run 303 from the petal to the caliper I doubt that you will get a satisfactory result. Regards Bent Regan LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com.