In our last segment, we reviewed common points of failure in the typical general aviation aircraft brake system. However, even if nothing has actually failed, you will eventually have to replace the brake linings, which wear away over time from normal use. In automobiles, brake linings are permanently attached to metal backing plates, and the entire assembly is disposable. On aircraft, the linings are riveted to reusable parts of the caliper assembly.
In order to replace the linings, the old ones must first be removed. This process is a good example of the importance of using the right tool for the job. Most aviation tool supply houses sell low-cost brake riveting tools that are specifically made to punch out the old rivets and press in the new ones. The problem with not using the proper tool is that it is very easy to elongate the rivet holes and damage the pressure or backing plates. Also, if you set the rivets with a hammer, you can easily crack the brake lining. If you plan to do your own work (under the supervision of an A&P), I recommend making the investment in one of these tools, since they can be found for under $30. I also recommend getting a supply of brake lining rivets in case you need a “do over.”
These tools are very simple to use: Simply position the backing or pressure plate in the tool and carefully screw down the shaft until the rivet is punched out. Installation of the new linings is just as simple: Remove the punch-out adapter from the tool, place a new rivet in the hole through the new liner, and twist the shaft until the rivet is properly set.
Be sure to consult the manufacturer’s manual for the proper break-in procedures for new brakes. It’s very important to get the new linings properly seated so that you’ll have maximum braking when you need it most.
You’ll need to consult the manufacturer’s maintenance manuals to determine the wear tolerances for your brake discs; however, rusted, pitted, or warped discs should always be replaced. Replacing the disc is easier than changing a tire.
After removing the wheel from the aircraft, start by deflating the tire completely. This step is critical to your safety! You’ll need to remove the through bolts in the wheel in order to remove and replace the disc. Any air pressure in the tire could cause the wheel to blow apart in your face as you remove the bolts, so be very careful.
One of the idiosyncrasies of the federal aviation regulations is that, while changing a tire is considered preventive maintenance, changing a brake disc is not. So, you can legally disassemble the wheel, set the brake disc aside, change the tire, and reassemble everything without an A&P sign-off. However, if you happen to reassemble the wheel using a new disc, you’ll be in violation of the regulations without the supervision of an A&P.
There are many different types of discs on the market today, including chrome discs that resist corrosion. Before selecting a new type of disc for your aircraft, be sure to consult the brake manufacturer to ensure compatibility of the brake disc and the brake lining. While some discs may resist corrosion better than others, they often have different braking properties.
Interested in aircraft maintenance? View the archives of Jeff Simon’s Aircraft Maintenance series.
Jeff Simon is an A&P mechanic, pilot, and aircraft owner. He has spent the last 14 years promoting owner-assisted aircraft maintenance as a columnist for several major aviation publications and through his how-to DVD series: The Educated Owner. Jeff is also the creator of SocialFlight, the free mobile app and website that maps over 20,000 aviation events, airport restaurants, and educational aviation videos, including many how-to videos for the subjects of these articles. Free apps are available for iPhone, iPad and Android, and on the Web at www.SocialFlight.com.