Hydraulic fluid bleed hose Exerciser jack Figure 13-26.  Air trapped in shock strut hydraulic fluid is bled by  exercising the strut through its full range of motion while the end  of an air-tight bleed hose is submerged in a container of hydraulic  fluid.  Figure 13-27.  This valve tool features internal and external thread  chasers, a notched valve core removal/installation tool, and a  tapered end for depressing a valve core or clearing debris.  13-15 9.  Remove the bleed hose assembly and fitting from the  service port of the strut. 10. Install the air service valve, torque, and inflate the  shock strut to the manufacturer’s specifications.  Landing Gear Alignment, Support, and  Retraction Alignment A straight edge is held across the front of the main wheel tires  just below axle height. A carpenter’s square placed against  the straight edge creates a perpendicular that is parallel to  the longitudinal axis of the aircraft. Slide the square against  the wheel assembly to see if the forward and aft sections of  the tire touch the square. A gap in front indicates the wheel  is towed-in. A gap in the rear indicates the wheel is towed- out.  [Figure 13-29]  The manufacturer’s maintenance instructions give the  procedure for checking and adjusting tow-in or tow-out. A  general procedure for checking alignment on a light aircraft  follows. To ensure that the landing gear settle properly for a  tow-in/tow-out test, especially on spring steel strut aircraft,  two aluminum plates separated with grease are put under each  wheel. Gently rock the aircraft on the plates to cause the gear  to find the at rest position preferred for alignment checks.  Alignment of the wheels of an aircraft is also a consideration.  Normally, this is set by the manufacturer and only requires  occasional attention such as after a hard landing. The  aircraft’s main wheels must be inspected and adjusted, if  necessary, to maintain the proper tow-in or tow-out and the  correct camber. Tow-in and tow-out refer to the path a main  wheel would take in relation to the airframe longitudinal  axis or centerline if the wheel was free to roll forward.  Three possibilities exist. The wheel would roll either: 1)  parallel to the longitudinal axis (aligned); 2) converge on  the longitudinal axis (tow-in); or 3) veer away from the  longitudinal axis (tow-out).  [Figure 13-28] As previously mentioned, a torque arm or torque links  assembly keeps the lower strut cylinder from rotating out of  alignment with the longitudinal axis of the aircraft. In some  strut assemblies, it is the sole means of retaining the piston in  the upper strut cylinder. The link ends are attached to the fixed  upper cylinder and the moving lower cylinder with a hinge  pin in the center to allow the strut to extend and compress. Retractable landing gear consist of several components that  enable it to function. Typically, these are the torque links,  trunnion and bracket arrangements, drag strut linkages,  electrical and hydraulic gear retraction devices, as well as  locking, sensing, and indicating components. Additionally,  nose gear have steering mechanisms attached to the gear.