TM 1-1500-204-23-1 Immediately after landing, as ice will form on tube when aircraft  is  left  standing  without  tube  being  cleaned  of water, mud and slush. (b)   Maintain proper air-oil levels in struts as specified   on   data   plates.      Use   hydraulic   fluid,   MIL- H5606. (c)   Replace pistons having nicks, scratches,   or   dents   deep   enough   to   cause   leakage. Replace  elongated  bushings.    Replace  struts  that  have cracked fittings. (d)   When   overhauling   a   pneumatic   shock strut,  all  ferrous  metal  parts  will  be  magnetic  particle Inspected   for   cracks   and   flaws.      Inspection   will   be accomplished in accordance with applicable maintenance manual. (2)   Rubber     block     type. Replacement of compression  and  rebound  rubber  blocks,  or  adjustment of   preload   tubes   shall   be   as   specified   in   applicable aircraft maintenance manual (3)   Spring  steel  type.    Repairs  are  limited  to burnishing   minor   nicks,   burrs,   or   scratches   Replace cracked struts. 9-6.      Landing   Gear   Alignment.      The   alignment   of aircraft  landing  gear  is  too  critical,  and  the  tolerances too narrow to deal with the subject in a general manner. Reference will be made to applicable aircraft maintenance manual for specific data relating to landing gear alignment. 9-7.  Brake Systems.  Brake system types and general maintenance are explained In the following paragraphs. a. Brake Types.  The three types of brake systems in  general  use  are  the  independent,  power  control,  and power boost systems.  Each is explained in the following paragraphs. (1)   Independent    systems.        In    general,    the independent   brake   system   is   used   on   small   aircraft. This    type    of    brake    system    is    termed    independent because    it    has    its    own    reservoir    and    is    entirely independent    of    the    aircraft    main    hydraulic    system. Independent   brake   systems   are   powered   by   master cylinders   similar   to   those   used   in   the   conventional automobile brake system.  The system is composed of a reservoir,   one   or   two   master   cylinders,   mechanical linkage   which   connects   each   master   cylinder   with   its corresponding brake pedal, connecting fluid lines, and a brake  assembly  in  each  main  landing  gear  wheel  as shown in figure 9-7. (2)   Power    control    systems.        Power    brake control valve systems, as shown in figure 9-8, are used on  aircraft  requiring  a  large  volume  of  fluid  to  operate the brakes.  As a general rule, this applies to many large aircraft.  Because of their weight and size, large wheels and  brakes  are  required.    Larger  brakes  mean  greater fluid  displacement  and  higher  pressures,  and  for  this reason   independent   master   cylinder   systems   are   not practical   on   heavy   aircraft.      In   this   system   a   line   is tapped off from the main hydraulic system pressure line. (3)   Power   boost   systems.         A   typical   power boost brake system, as shown in figure 9-9, consists of a reservoir, two power boost master cylinders, two shuttle valves,  and  the  brake  assembly  in  each  main  landing wheel.    In  this  type  of  system,  a  line  is  tapped  off  the main hydraulic system pressure line, but main hydraulic system   pressure   does   not   enter   the   brakes.      Main system   pressure   is   used   only   to   assist   the   pedals through the use of power boost master cylinders. b. Brake Assemblies. Brake assemblies commonly used on aircraft are the single-disk, dual-disk. The single and dual-disk types are more commonly used on small aircraft. (1)   Single-disk   brakes.      With   the   single-disk brake,  braking  is  accomplished  by  applying  friction  to both   sides   of   a   rotating   disk   which   is   keyed   to   the landing gear wheel.  There are several variations of the single-disk   brake,   however,   all   operate   on   the   same principle  and  differ  mainly  In  the  number  of  cylinders and the type Figure 9-7.  Independent Brake System 9-7