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. Maintenance 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. DISASSEMBLY.—Place the brake assembly with the brake housing down and remove the brake housing bolts. Remove the backing plate and all discs from the torque tube, and then remove the torque tube. Turn the brake over and remove the self-locking nuts to release the return pins. Remove the tube and grip assemblies, pressure plate, and the remaining return spring parts. The tube and grip assemblies should not be disassembled. If they require replacement, replace the complete assembly as a unit. 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. CLEANING AND INSPECTION.—Dust and loose grit are removed by using low-pressure air, and then all parts are cleaned in a P-D-680 cleaning solvent and dried with a clean, lint-free cloth. All metal parts are visually inspected for cracks, wear, or other damage, as specified in the “Intermediate Repair” section of the MIM. Some parts may require inspection by one of the nondestructive methods. The return spring is inspected for proper resilience. The amount of force required to move the grips on each tube and grip assembly is checked with a special tube and grip tester. The rotating disc is inspected for cracks, distortion, and thickness. The disc must be replaced if it is worn below 0.2-inch thickness, if it is cracked, or if the friction mix is worn unevenly. The friction mix maybe pitted up to 0.5 square inch in any segment. The stationary disc is inspected for cracks and thickness. If the minimum thickness is less than 0.3 inch or the disc is cracked, it should be replaced. The backplate and pressure plate should be replaced if they are cracked. If the wear pads are worn to less than 0.088-inch tltickness, they should be replaced. WEAR PAD REPLACEMENT.—Wear pad re- placement on the pressure plate and the backing plate is authorized. Drill out rivets that hold the worn pads. Discard the worn pads. Check the plates for cracks, deformation, and rivet hole elongation. Use a standard squeeze rivet machine to rivet the replacement wear pads to the plates, using the type of rivet specified in the applicable MIM. The rivet bucktail must be below the surface of the wear pad, Rivets with more than one crack visible in the bucktail or with less than 50 percent of the circumference of the formed head flush with the sides of the countersunk area are not acceptable. The new wear pads must be surface ground to 0. 100-inch thickness, and should be flat within 0.010 inch after grinding. The reworked plates should be vapor degreased to remove all oil and grinding material. The dried plates should be wrapped in clean, heavy paper for protection until they are replaced in the brake assembly. REASSEMBLY.—Reassembly of the trimetallic brake is essentially in the reverse order of disassembly. Lubricate the packings, retainers, cylinder walls, and other contacting surfaces within the brake housing with a light coating of MIL-G-8 1322, general-purpose aircraft grease before reassembly. Apply MIL-G-6032B grease to the piston side of the piston insulators. Lubricate the brake housing bolts and the contacting surfaces of the bolt heads with antiseize compound. The coating of these bolts and the contacting surface of the bolt heads, followed by torquing, are referred to in some MIMs as “Lubtork.” TESTING.—The reassembled trimetallic brake must be tested to ensure the quality of maintenance. Connect the brake assembly to a hydraulic test stand and apply 25 psi to the inlet port. Open the bleeder valve until air-free fluid flows from the valve. Increase the pressure to 1,000 psi for 2 minutes and check for leaks. Relieve and reapply 1,000 psi several times, and then release the pressure slowly to 90 psi. Holding the 90-psi pressure, measure the clearance between the pressure plate and the first rotating disc. Minimum clearance must be 0.065 inch. If used discs were reinstalled, check for proper rotation. Secure the test stand, disconnect the brake, and plug the inlet port to prevent contamination. 12-62