in and out of bushings in the torque plate, which is bolted to the  axle flange. The cylinder assembly is bolted to the backplate to  secure the assembly around the disc. When pressure is applied,  the caliper and linings center on the disc via the sliding action  of the anchor bolts in the torque plate bushings. This provides  equal pressure to both sides of the disc to slow its rotation.  Dual-disc brakes are used on aircraft where a single disc on  each wheel does not supply sufficient braking friction. Two  discs are keyed to the wheel instead of one. A center carrier  is located between the two discs. It contains linings on each  side that contact each of the discs when the brakes are applied. The caliper mounting bolts are long and mount through the  center carrier, as well as the backplate which bolts to the  housing assembly.  [Figure 13-83]  Large, heavy aircraft require the use of multiple-disc brakes.  Multiple-disc brakes are heavy duty brakes designed for  use with power brake control valves or power boost master  cylinders, which is discussed later in this chapter. The brake  assembly consists of an extended bearing carrier similar to a  torque tube type unit that bolts to the axle flange. It supports  the various brake parts, including an annular cylinder and  piston, a series of steel discs alternating with copper or  bronze-plated discs, a backplate, and a backplate retainer.  The steel stators are keyed to the bearing carrier, and the  copper or bronze plated rotors are keyed to the rotating  wheel. Hydraulic pressure applied to the piston causes the  entire stack of stators and rotors to be compressed. This  creates enormous friction and heat and slows the rotation of  the wheel.  [Figure 13-84]  A unique feature of the Cleveland brake is that the linings  can be replaced without removing the wheel. Unbolting the  cylinder assembly from the backplate allows the anchor  bolts to slide out of the torque plate bushings. The entire  caliper assembly is then free and provides access to all of  the components.  Maintenance requirements on all single disc brake systems  are similar to those on brake systems of any type. Regular  inspection for any damage and for wear on the linings and  discs is required. Replacement of parts worn beyond limits  is always followed by an operational check. The check is  performed while taxiing the aircraft. The braking action for  each main wheel should be equal with equal application of  pedal pressure. Pedals should be firm, not soft or spongy,  when applied. When pedal pressure is released, the brakes  should release without any evidence of drag. Housing back plate Housing assembly Brake lining Brake lining Brake disc Brake disc Wheel axle Piston Self-adjusting pin Spring Washer Bleeder screw Brake lining Brake lining Center carrier Figure 13-83.  A dual-disc brake is similar to a single-disc brake. It uses a center carrier to hold brake linings against each of the discs. 13-46 Dual-Disc Brakes Multiple-Disc Brakes