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BRAKES AND MASTER CYLINDERS
From CP78, Page 4, April, July 1994
EZ's require serious diligence when it
comes to brake maintenance because the brakes are not only used to slow or stop the
airplane, but they are the only means of steering while taxiing.
Recently, there have been two incidents involving brake failures resulting in loss of control, running off runways, through ditches, causing no injuries but seriously damaging both airplanes. The damage included ripped out landing gears, broken wings/winglets and even a broken canard.
Maintaining the brakes is absolutely essential to the safe operation of an EZ and is easy to forget or ignore because most EZ's have wheel pants fitted that hide the brakes. Make it a habit to routinely and regularly remove these wheel pants and carefully check the brake linings for wear. Look for any sign of hydraulic leaks. These will appear as a dark stain at the threads of a "B" nut or fitting. Do not use shop air to blow the dust out of the wheel, this dust consists of asbestos or asbestos-like particles which could be very harmful to your lungs over the long term. Rather, use a high pressure water jet (a garden hose) to flush most of the dust, then use a commercial brake cleaner in a spray can (available at auto parts store) to completely clean the entire brake caliper, brake disc and wheel. Replace worn brake linings and fix any hydraulic leaks. Allow the brake assembly to dry out completely before going flying.
If you have Nylaflow brake lines, you should change them out every year when you do your annual inspection. Nylaflow is easily damaged by ultra violet (sunshine) and is prone to damage from the radiating heat of the sometimes red hot brake disc. To be safe, change them out as often as necessary. I, long ago, went to Stratoflex Teflon/stainless braided brake lines and have never regretted this upgrade.
Brake master cylinders are all too often
ignored. Every couple of years, or more often if you have a brake problem, you should
remove and dismantle these critical parts. Replace any suspect "O" rings and
thoroughly clean all the parts. (Denatured alcohol works well). Use a bright light and
examine the bore of each master cylinder. If there is any scoring or other contamination
such as rust, consider honing the bores prior to reassembly.
Aircraft hydraulic brakes are always filled from the bottom of the brake caliper. The hydraulic lines should run continuously uphill to the master cylinder to assure that the fluid drives all of the air out of the system as it is forced into the small brake bleeder on the lowest part of the brake caliper. Have an assistant watch for the fluid as it gets to the brake master cylinder or reservoir. They should do this using a flash light and looking through the small threaded hole usually plugged with a plastic plug.
If you have to do this job alone, you need to make up a clear plastic tubs with a fitting on one end that will screw into the 1/8" pipe threaded hole in the reservoir. The plastic line should be long enough to reach out of the reservoir and down to the can on the floor. You must be able to see this plastic line as you pump brake fluid into the brake caliper. (I use a large trigger-operated oil can and it never gets used for anything else!). Continue to pump until you can see brake fluid flowing through the overflow line you have installed. Usually there are a few bubbles in this line. Continue to pump until there are no air bubbles. Now, as you are pumping, tighten the /4" nut that is the bleeder. Do not over tighten this nut, it only needs to be firmly snug. Remove the overflow fitting and plastic line and siphon a little fluid out, lowering the fluid level about 1/2" in the reservoir. I use a 3 foot length of Nylaflow to suck the fluid out. Be careful not to get any in your mouth, it tastes awful! Replace the plastic plug, be sure that it has a small breather hole (1/16" dia. is fine) drilled through it.
Careful maintenance is the key to safe flying and don't forget, the airplane will usually let you know before it bites you. If you notice a change in your brakes, don't fly - fix it first!