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ples of operation apply. Question vehicle crew to obtain maxi-
The greater the num-
mum  number  of  observed  symptoms.
ber of symptoms of troubles that can be evaluated, the easier
will
be
the
isolation
of
the
defective
system
and
components
thereof.
46.
Brakes
In  analyzing  trouble  with  the  braking  system
a.  General.
of  the  unit,  it  is  especially  important  to  localize  the  cause
because
of
the
complexity
of
the
system.
It
must
be
remem-
bered  that  the  symptom  may  be  the  end  result  of  a  defect
existing on the towing vehicle instead of the semitrailer. By
the elimination of one possible general source of trouble after
another, and then eliminating specific possibilities in the af-
fected  portion  of  the  system,  the  actual  cause  of  the  trouble
may be isolated and corrected.
b. Brakes Will Not Release.
(1) Emergency  relay  valve  in  applied  position.
(a)  Build  up  pressure  in  semitrailer  brake  system,
if
semitrailer is coupled.
(b)
Open
drain
cock
on
semitrailer
air
reser-
voir, if semitrailer is uncoupled.
(2) Intervehicular air hose improperly connected to tow-
ing vehicle or semitrailer. C o n n e c t
properly
(par.  31b(4)).
(3) Brake
valve
on
towing
vehicle
in
applied
position.
Move brake valve to released position,
(4) Restriction in lines or hose. Check and clean all lines
a n d hose.
(5) Shutoff valves closed on towing vehicle. O p e n v a l v e s .
(6) Weak or broken brake shoe tension spring. R e p l a c e
spring  (pars.  57a  and
d
(M269
and
M270)
and
TM
9-1827C (M270A1)).
c. No Brakes or Weak Brakes.
(1) Shutoff valves closed on towing vehicle. O p e n v a l v e s .
(2) Intervehicular air hose improperly connected to tow-
ing vehicle or semitrailer. C o n n e c t  c o u p l i n g s  p r o p e r l y
(par  31b(4)).
(3) Semitrailer air reservoir drain cock open. C l o s e d r a i n
cock (fig. 12).
(4) Low
air
pressure.
Check air pressure gage on tow-
ing vehicle. Make leakage tests (pars. 60c, 61b, 62a,
63a, and 65).
Check  for  restriction  in
air  lines.
(5) Defective  emergency  relay  valve. M a k e
serviceability
tests
60b).
TACO 1321B
74



 


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