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Page Title: AXLE-REAR (With Locking Differential)
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TM 5-4210-230-14&P-1 VEHICLE OPERATION AXLE-REAR (With Locking Differential) CAUTION To avoid personal injury or property damage, pay strict attention to the following: If   your   vehicle   is   equipped   with   a   locking differential,  power  will  be  transmitted  to  the opposite wheel should one of the wheels slip. Both wheels must be raised free of the ground should  it  be  necessary  to  operate  one  wheel with    the    vehicle    stationary;    otherwise    the wheel that is not raised will pull the vehicle off its supports. As  with  any  vehicle,  care  should  be  taken  to avoid  sudden  accelerations  when  both  drive wheels are on a slippery surface.  This could cause both drive wheels to spin, and allow the vehicle   to   slide   sideways   on   the   crowned surface of a road or in a turn. BRAKES (Air) The purpose of this dual system is to provide a means of stopping the vehicle should a failure occur in one of the two independent  brake  systems.    In  the  event  air  pressure  loss occurs   in   one   system,   the   remaining   system   continues   to provide braking action. The  air  system  splits  at  the  supply  reservoir  where  it branches   into   separate   service   reservoirs.      Each   service reservoir  supplies  air  to  a  separate  section  of  the  dual  brake valve. The  brake  valve  is  equipped  with  two  separate  supply and delivery systems for service and emergency braking, thus providing  the  operator  with  a  graduated  control  for  applying and  releasing  the  vehicle  brakes,  even  in  the  event  of  an  air loss in either the primary or secondary system. The   primary   air   system   on   all   trucks   and   tractors supply  air  to  rear  axle  brakes  and  the  secondary  air  system supplies air to the front axle brakes. Tractor systems are designed to control the towed unit from  both  braking  systems.    Should  failure  occur  in  either system,   control   of   the   trailer   service   brakes   is   maintained through the use of air from the remaining system. On   a   straight   truck   the   primary   (rear)   brakes   are designed to stop the truck in required distance in the event of air loss in the secondary system. If  a  loss  of  air  occurs  in  the  primary  system,  the  air system  on  a  straight  truck  is  designed  to  allow  the  spring brakes   on   the   rear   axle   to   be   applied   or   released   in   a modulated manner at the same time the front service brakes are applied or released by the operator. Even though there will be enough braking capability for emergency stopping, the vehicle should not be operated when a failure is indicated. All    vehicles    are    equipped    with    spring    brakes    for parking.  The parking system is operated manually by a single valve, which in the case of a tractor also controls the parking system    on    the    towed    unit.        This    total    vehicle    parking capability,   using   the   parking   valve   as   the   master   control, requires the parking brake be released and trailer emergency valve in the "released" position to permit charging of the trailer air  system.    The  need  for  an  emergency  release  reservoir  is eliminated  due  to  its  function  being  provided  by  either  of  the two    service    brake    systems.        The    parking    brakes    will automatically  apply  only  if  both  service  system  air  pressures are depleted. BRAKE ANTILOCK SYSTEM The   antilock   system   has   been   added   to   air   braked vehicles  as  an  aid  in  helping  to  keep  the  vehicle  in  its  traffic lane during severe braking. It assists the driver by keeping the wheels  from  sliding  during  hard  brake  applications  without sacrificing   stopping   distance.      Some   wheel   lock   may   be experienced at very low speeds. The antilock system analyzes wheel speed information and   detects   a   rapid   change   in   wheel   speed   such   as   that caused   during   hard   braking.      It   will   decrease   air   pressure momentarily  reducting  brake  power  allowing  the  wheels  on affected axles to roll more freely, thus preventing the wheel or brake lock-up which would result in loss of vehicle control as well as flat spotting of tires.  Just as soon as the wheels return to  a  controlled  percentage  of  their  original  speed,  the  brakes are   automatically   reapplied.      A   sequence   of   releasing   and reapplying air pressure of the brakes is known as an antilock cycle   and   may   be   repeated   several   times   during   a   stop, depending   upon   the   initial   speed,   road   surface   and   brake force applied by the driver. Each cycle can be felt by the driver as a "lurch" or the same  type  of  feeling  that  would  be  obtained  when  the  brake pedal is rapidly pumped during a stop.  On icy roads cycling may  continue  long  enough  that  reservoir  pressure  could  be depleted to a point that the low air pressure buzzer and light will come on.  This is not a cause of immediate alarm since braking is still available even at this reduced pressure. Poor  brake  adjustment  will  aggravate  air  consumption since  long  chamber  strokes  will  require  more  air  to  be  used during each cycle.  This means that reservoir air pressure will be  depleted  faster  than  would  be  the  case  with  good  brake adjustment and short chamber strokes. 1

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