SERVICE MANUAL The  service  nylon  tubing  will  be  marked  at  regular intervals with name, number, type, size and manufacturing code designations.This marking is intended   to   positively   identify   the   tubing   and   prevent substitution of inferior quality tubing. TRAILER   BRAKE   HOSE   COUPLING   AND   DUMMY COUPLING Hose   couplings   provide   a   convenient   means   for connecting  and  disconnecting  air  lines  between  tractors and    trailers.    When    two    couplings    are    joined,    their packing rings are forced together under pressure to form an air tight seal. Dummy coupling is the term given to those couplings which  are  used  to  keep  dirt  or  foreign  matter  out  of  the air lines when they are not being used. Dummy couplings are  either  rigidly  mounted  to  the  truck  or  fastened  by  a chain. TEST 1. With    hose    couplings    connected    and    brakes applied,  coat  the  hose  couplings  with  soapsuds to check for leaks. No leaks allowed. 2. Leakage results from worn, damaged, or improperly installed packing rings. REPLACEMENT 1. At   least   once   a   year   or   if   leaking,   the   hose coupling  should  be  disassembled,  cleaned  and serviced. 2. Remove  old  packing  ring  by  prying  out  with  a screwdriver.   Be   sure   packing   ring   groove   is thoroughly cleaned. 3. Install  new  packing  ring  by  partially  collapsing  it with  the  fingers,  (Fig.  8  )  and  entering  one  side of flange in groove in coupling. 4. Work the remaining part of the packing ring into place  with  a  blunt  nosed  screwdriver  or  similar tool (Fig. 9). Exposed face of packing ring will be flat    and    free    of    any    bulges    when    properly installed. TRAILER BRAKE HOSE ASSEMBLIES AND CONNECTORS Trailer  brake  hose  assembles  are  used  for  making flexible  connections  between  components  on  the  truck which  change  positions  in  relation  to  each  other  or  for making   flexible   connections   between   the   tractor   and trailer.  Hose  lines  or  couplings  at  the  rear  of  tractor  are marked    by    tags    identifying    them    as    "SERVICE"    or "EMERGENCY". Fig. 8 Installing Packing Ring In Hose Coupling 1Packing Ring 2Hose Coupling Fig. 9 Using Screwdriver to Complete Packing Ring Installation 1Blunt Nosed Screwdriver 2Packing Ring 3Hose Coupling Test 1. If a line is suspected of being restricted, remove and  blow  air  through  it  in  both  directions.    Air passage through hose must not be obstructed in any way. 2. To  check  for  leaks,  apply  the  brakes  and  coat hose and connections with soap suds. No leaks are permitted. Leakage at hose connectors is CTS-4079 - CHAPTER XII - Page 6