SERVICE MANUAL When   maximum   traction   is   required   such   as   for pulling  through  deep  sand,  mud  or  snow,   the   lockout control on dash is operated to engage the power divider lock.  This activates the shift fork shaft and fork in power divider  to  lock  up  the  inter-axle  differential  and  provide positive drive to both forward and rear axle units. The lockout mechanism must be engaged only when the truck is standing still.  It should be kept engaged only as   long   as   positive   traction   is   required.      Continuous unnecessary   engagement   will   result   in   excessive   tire wear and may damage the axles. The  power  divider  lockout  is  controlled  by  either  a valve or switch on the vehicle instrument panel.  A "tell- tale" warning light is also provided on instrument panel to indicate when power divider lock is engaged. Three   different   kinds   of   power   shift   systems   are used to  actuate  the  power  divider  lock.    These  systems are covered in paragraphs which follow. ELECTRIC SHIFT SYSTEM The   electric   shift   system   consists   of   an   electric powered  motor  unit  mounted  on  the  forward  rear  axle with a control switch on dash. For complete information on the electric shift system (Maintenance,    Trouble    Shooting,    Rebuild,    etc.    See REAR AXLES CTS-4041 in the Service Manual). VACUUM SHIFT SYSTEM The   vacuum   shift   system   consists   of   a   vacuum power   unit   mounted   on   the   forward   rear   axle   with   a control   valve   located   on   the   instrument   panel.      The power  source  for  the  vacuum  shift  system  is  vacuum from the engine intake manifold for gasoline engines or a vacuum  pump  for  diesel  engines.    If  either  the  vacuum power  unit  or  vacuum  control  valve  are  defective  they must be replaced. AIR SHIFT SYSTEM The air shift system consists of an air power cylinder mounted  on   the   forward   rear   axle   with   an   air   control valve on the instrument panel.  The power divider lock is disengaged   by   air   pressure   and   spring   controlled   for engagement ("lock in"). When    the    PDL    (Power    Divider    Lock)    control    is placed    in    the    "lock"    position    air    in    the    system    is exhausted and the PDL will shift to the "lock" mode. When   the   PDL   control   is   placed   in   the   "unlock" position, air pressure will hold the PDL in the disengaged mode. The   air   control   valve,   control   cylinder,   hoses   and pipe    connections    of    air    control    systems    should    be inspected  periodically  for  leakage  and  other  repairs.    At time  of  axle  overhaul,  control  cylinder  and  control  valve should   be   inspected   carefully   and   worn   or   damaged parts replaced. MAINTENANCE AXLE SHAFTS Axle  failure  can  also  be  attributed  to  the  axle  shaft. For   this   reason   it   is   most   important   that   shafts   be installed   properly,   be   of   correct   size   and   lengths   for splines  to  engage  fully  and  be  kept  free  from  runout  or bends. AXLE HOUSING The axle housing is of one piece construction with an opening  in  the  center  for  mounting  the  diff  carrier.    A flange is welded to the outer ends of the axle housing for mounting the brake backing plates.  A bent axle housing can  be  the  cause  of  early  axle  failure  and  whenever  an axle  is  rebuilt  this  condition  should  always  be  checked before going ahead with the assembly. The condition of axle housing cover weld should also be checked.  If cover weld is cracked, oil seepage from housing   can   occur.      Re-welding   of   housing   cover   is permitted   providing   special   cleaning   precautions   and recommended welding procedures are observed. Procedure   for   repairing   cracked   weld   or   leaking housing cover is as follows: 1. Drain differential and remove diff carrier assembly. 2. Clean     lube     from     inside     of     housing     and     burn remaining lube from inside with torch. 3. Clean residual lube from housing with solvent. 4. Grind  or  air  arc  cracked  weld  from  outside  of  cover weld to base metal. 5. Weld  three  passes  around  outside  of  cover  using 1/8"  Spec.    No.    E7016  Weld  Rod  and  supplier’s recommended   amperage   and   voltage.   Thoroughly clean weld area between passes. CTS-4044 PRINTED IN UNITED STATES OF AMERICA Page 27