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TM 10-3930-671-24
Troubleshooting Procedures
The two most important transmission troubleshooting
procedures are 1) check fluid level and 2) run a stall test.
1.
Fluid Level Check - Before checking the
transmission
clutches,
torque
converter,
charging pump and hydraulic circuit for speeds,
pressures and/or rate of oil flow, it is important to
check
the
oil
level
in
the
transmission
(transaxle). The transmission fluid must be at
the correct (full) level. All clutches and the
converter and its fluid circuit lines must be fully
charged (filled) at all times.
The transmission fluid must be at
operating temperature of 180-200°F
(82-93°C) to obtain correct fluid level
and pressure readings. Do not
attempt to make these checks with
cold oil.
2.
To raise the oil temperature to this specification,
it is necessary to either operate (work) the truck
under load, or briefly run the engine with the
converter at stall. See converter stall procedure
for warming the oil below.
Converter Stall Procedure
NOTE
Running the truck when up on blocks
will not be adequate to warm the oil.
Part Throttle Converter Stall Procedure To Warm
Transmission Oil
Stall operation must be performed with the parking brake
applied and wheels blocked up above the ground surface
to prevent movement. Use of the service brakes (with
inching) will release the transmission clutches and
prevent stalling of the torque converter.
Be careful that the truck does not
move unexpectedly when operating
the engine and converter at stall rpm.
Unexpected movement could cause
injury or death to personnel.
1.
Apply the parking brake and block/support the
drive axle on blocks so that the drive wheels do
not touch the ground surface.
2.
Put directional control lever in FORWARD (or
REVERSE, as applicable).
3.
If 2-speed transmission, put speed control lever
in "2" (HIGH).
4.
With engine running, slowly increase engine
speed to approximately one-half throttle (1200-
1500 rpm) and operate as noted (see CAUTION
below) until transmission (converter outlet) oil
temperature reaches the operating range.
Full Throttle Converter Stall Procedure
1.
Proceed as per Steps 1, 2, & 3 above, except
check stall speed at full throttle during test.
Do not operate the converter at stall
condition longer than 30 seconds at
one time. Then, shift transmission
into neutral for 15 seconds with
engine speed at approximately one-
half throttle. Repeat procedure until
desired operating temperature has
been
reached.
Excessive
temperature (250°F max. [120°C]) will
overheat the converter and cause
damage to converter, seals and fluid.
2.
Full Throttle Stall Test Use a full throttle (full
power)
stall
test
to
identify
transmission,
converter or engine problems.
Refer to Section 4. 7, Engine RPM, Vacuum & Stall
Tests.
3.
Transmission Pressure Checks Transmission
problems can be isolated by the use of pressure
tests. When the stall test indicates slipping
clutches, then measure clutch pack pressure to
determine if the slippage is due to low pressure
or clutch plate friction material failure. In
addition,
converter
charging
pressure
and
transmission lubrication pressure may also be
measured.
Refer to Section 7.3, Transmission Pressure Checks.
4.
Mechanical Checks - Prior to checking any part
of the system for hydraulic function (pressure
testing), the following mechanical checks should
be made:
a)
Be sure all control lever linkage is properly
connected and adjusted in each segment
and at all connecting points.
b)
Check shift levers and rods for damage
and restrictions that could prevent full
travel movement. Move the levers by
hand at the control valve. If the control
spool does not actuate fully, the problem
may be in the control cover and valve
F-324
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