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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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