The brake housing must be inspected thoroughly. Scratches,  gouges, corrosion, or other blemishes may be dressed out and  the surface treated to prevent corrosion. Minimal material  should be removed when doing so. Most important is that  there are no cracks in the housing. Fluorescent dye penetrant  is typically used to inspect for cracks. If a crack is found, the  housing must be replaced. The cylinder area(s) of the housing  must be dimensionally checked for wear. Limits are specified  in the manufacturer’s maintenance manual.  excessive key slot wear are grounds for rejection. Brake wear  pads or linings must also be inspected for wear while the  brake assembly is removed from the aircraft. Signs of uneven  wear should be investigated, and the problem corrected. The  pads may be replaced if worn beyond limits as long as the  stationary disc upon which they mount passes inspection.  Follow the manufacturer’s procedures for inspections and  for pad replacement. Rotating discs must be similarly inspected. The general  condition of the disc must be observed. Glazing can occur  when a disc or part of a disc is overheated. It causes brake  squeal and chatter. It is possible to resurface a glazed disc  if the manufacturer allows it. Rotating discs must also be  inspected in the drive key slot or drive tang area for wear and  deformation. Little damage is allowed before replacement  is required.  The brake pistons that fit into the cylinders in the housing  must also be checked for corrosion, scratches, burrs, etc.  Pistons are also dimensionally checked for wear limits  specified in the maintenance data. Some pistons have  insulators on the bottom. They should not be cracked and  should be of a minimal thickness. A file can be used to smooth  out minor irregularities.  The pressure plate and back plate on multiple disc brakes  must be inspected for freedom of movement, cracks, general  condition, and warping. New linings may be riveted to the  plates if the old linings are worn and the condition of the  plate is good. Note that replacing brake pads and linings by  riveting may require specific tools and technique as described  in the maintenance manual to ensure secure attachment.  Minor warping can be straightened on some brake assemblies. Brake seals are very important. Without properly functioning  seals, brake operation will be compromised, or the brakes  will fail. Over time, heat and pressure mold a seal into the  seal groove and harden the material. Eventually, resilience  is reduced and the seal leaks. New seals should be used to  replace all seals in the brake assembly. Acquire seals by  part number in a sealed package from a reputable supplier to  avoid bogus seals and ensure the correct seals for the brake  assembly in question. Check to ensure the new seals have  not exceeded their shelf life, which is typically three years  from the cure date. A malfunctioning automatic adjuster assembly can cause the  brakes to drag on the rotating disc(s) by not fully releasing  and pulling the lining away from the disc. This can lead to  excessive, uneven lining wear and disc glazing. The return  pin must be straight with no surface damage so it can pass  through the grip without binding. Damage under the head  can weaken the pin and cause failure. Magnetic inspection  is sometimes used to inspect for cracks.  Many brakes use back-up rings in the seal groove to support  the O-ring seals and reduce the tendency of the seal to extrude  into the space which it is meant to seal. These are often made  of Teflon® or similar material. Back-up seals are installed  on the side of the O-ring away from the fluid pressure.  [Figure 13-121]  They are often reusable.  The components of the grip and tube assembly must be in  good condition. Clean and inspect in accordance with the  manufacturer’s maintenance instructions. The grip must  move with the force specified and must move through its  full range of travel. In general aviation, replacement of brake linings is commonly  done in the hangar. The general procedure used on two  common brake assemblies is given. Follow the actual  manufacturer’s instruction when replacing brake linings on  any aircraft brake assembly. A sound torque tube is necessary to hold the brake assembly  stable on the landing gear. General visual inspection should  be made for wear, burrs, and scratches. Magnetic particle  inspection is used to check for cracks. The key areas should  be checked for dimension and wear. All limits of damage  are referenced in the manufacturer’s maintenance data. The  torque tube should be replaced if a limit is exceeded. To replace the linings on a Goodyear single disc brake  assembly, the aircraft must be jacked and supported.  Detach the anti-rattle clips that help center the disc in the  wheel before removing the wheel from the axle. The disc  Goodyear Brakes Replacement of Brake Linings Torque Tube Automatic Adjuster Pins Seal Condition Brake Housing and Piston Condition 13-72