Figures 12-53 and 12-54 show a typical trimetallic brake assembly. The trimetallic brake assembly consists of a brake housing subassembly, a keyed torque tube and torque tube spacer, a housing backplate, stationary and rotating discs, and a pressure plate subassembly.

The brake pistons transmit hydraulic pressure through the pressure plate subassembly to the brake discs. Standard O-rings and backup rings around each piston prevent hydraulic fluid leakage and entry of contaminants. The pistons are further protected against heat transfer from the pressure plate subassembly by individual insulators installed in the ends of each piston where it contacts the pressure plate.

Self-adjusting mechanisms are located around the brake housing. They accomplish normal release of the brake and provide a continuing adjustment action to compensate for broke wear. Each mechanism consists of a self-adjusting pin, a spring housing and bushing, a return spring guide, a retaining ring, a grip and tube subassembly, and a self-locking nut. The grip and tube subassembly mounts over the self-locking pin, with the grips being installed firmly on the tube. As disc wear occurs automatic adjustment is provided by movement of the adjusting pins through the split collar grips. The retaining ring inside the spring housing serves as a stop and retainer for the spring guide, which, in turn, holds the return spring in position. The head of the self-adjusting pin engages the pressure plate subassembly to allow brake release when pressure is removed.

When the landing gear wheel is rotating, the metallicfaced rotating discs of the brake assembly rotate freely between the stationary steel discs. When pressure is applied to the brake assembly pistons, the rotating and stationary discs are forced together, creating friction between their surfaces. The amount of hydraulic pressure applied to the brake pistons is controlled by the aircrafts brake metering system in response to the operating of the brake pedals. Braking action applied to the wheel brake is proportional to the pressure exerted on the brake pedal.

Pressure applied to the brake actuates all of the pistons within the brake housing. These pistons, in turn, force the pressure plate subassembly laterally against the discs and against the housing backplate. As the pressure is applied and the brake starts to actuate, the lateral movement of the pressure plate subassembly pulls the self-adjusting pins, the split collar grip and tube subassemblies, and the return spring guides against the return springs, compressing them until the spring guides bottom in the housings. When the hydraulic pressure is relieved, the return spring mechanisms, acting through the heads of the self-adjusting pins, pull the pressure plate subassembly back to the released position. The pistons also return to their deactuated positions. The extent of the return motion is limited by engagement of the spring guides with the retaining ring stops inside the spring housing.

As the discs wear, self-adjusting pins and tubes are pulled through the split collar grips by the force exerted on the pressure plate by the pistons. This small movement of the adjusting pins and tubes, relative to the grips, is equivalent to the combined wear of all the discs. When pressure is removed from the brake, the return springs return the pressure plate and the brake pistons to the designed reset clearance and maintain a constant displacement.

Intermediate maintenance of the trimetallic brake assembly consists of disassembly, cleaning and inspec-tion, wear pad replacement as necessary, reassembly, and testing. A brief description of each follows.

The piston insulator is removed from the pistons, and the pistons are removed from the brake housing by threading a return pin into the threaded hole in the piston and pulling slowly. Exercise care to avoid damage to the seal groove and cylinder walls. Remove the bleed valve assembly and the brake inlet plug assembly.