TM 5-3895-383-24 Problem The   propel   system   engages   very   suddenly   when   the operator is making a shift. Probable Cause The orifices are missing from the piston pumps. The shuttle valve spool that is inside the flushing valve is sticking. The servo valve spool is sticking. Problem The propel system operates in one direction only. Probable Cause The pump servo valve has failed. The pump servo piston has failed. The    rocker    arm    section    of    the    pump    swashplate assembly has failed. One of the multifunction valves is damaged. The shuttle valve spool is sticking. The control valve has failed. Problem The  propel  system  does  not  disengage  when  the  propel control lever is returned to neutral. Probable Cause The pump servo valve has failed. The pump s ervo piston has failed. The    rocker    arm    section    of    the    pump    swashplate assembly has failed. The neutral adjustment of the servo valve is incorrect. The linkage rod between the directional control valves is incorrectly adjusted. Problem The   parking   brake   does   not   release   when   the   parking brake button is pulled up. Probable Cause The parking brake button has failed. There is a malfunctioning piston seal in the brake group. The parking brake valve has failed. There is a fault in the electric circuit. The neutral start switch has failed. The neutral start relay has failed. Low charge pressure. The brake relay has failed. The   relief   valve   on   the   gear   pump   is   damaged   or incorrectly adjusted. Failure of the gear pump. Problem The   parking   brake   does   not   engage   when   the   parking brake button is pushed down. Probable Cause The parking brake button has failed. The brake relay has failed. The brake discs are worn. There is a pinched brake line. The parking brake valve has failed. There is a fault in the electrical circuit. Problem There   are   external   oil   leaks   from   either   of   the   piston motors. Probable Cause Motor case pressure is too high. There is a restriction in the oil return line to the hydraulic oil tank. There are damaged seals due to pressure peaks, use of unapproved   hydraulic   oil,   or   an   incorrect   tightening torque. Problem The oil in the propel system overheats. Probable Cause An incorrect type of oil is used in the hydraulic circuit. The oil cooler is internally restricted. The radiator and/or the oil cooler is externally restricted. There  is  a  low  charge  line  pressure  that  is  caused  by excessive internal leakage in the circuit. 10-59