Powershift Gearbox
Torque Converter Stall Test
The purpose of the stall test is to check the performance of
the transmission by ‘stalling’ the torque converter. This is the
point at which, due to torque applied by the engine the
torque converter stops transmitting drive to the gearbox.
The engine speed at which ‘stalling’ occurs is compared to
speeds recorded for a machine in normal condition (given in
Technical Data
). Abnormal stall speed results can be used
to identify a number of possible faults with the transmission,
typically gearbox hydraulic and clutch faults.
Note:
DO NOT stall the converter for longer than 10 seconds
or the transmission fluid will overheat. Make sure that the oil
level is correct and at normal operating temperature.
Before completing the following test, remove the
transmission dipstick. If there is any sign of smoke emitting
from the dipstick tube STOP THE TEST IMMEDIATELY and
dismantle the transmission for servicing.
By performing the tests in the first 3 gears in forward and
reverse we can see from the tables below that all the
clutches in the gearbox will be engaged, ensuring faults will
be easy to identify. Draw a table as shown so that you can
record the results.
1
Ensure that the engine and transmission are at normal
working temperature (the transmission oil must be
above 50°C). Run engine at maximum speed and check
the
No Load Speed (High Idle Speed - U.S.A).
See
Engine Technical Data for correct figure; adjust if
necessary.
2
Apply parking brake and footbrake firmly. If necessary,
set the machine against a fixed obstruction.
65 - 1
Note:
When fully engaged, the parking brake electrically
disconnects the transmission drive; this prevents the
machine from being driven with the parkbrake on. Therefore,
so that we can complete the test, move the parkbrake lever
fractionally forward until the warning light is just
extinguished; hold the lever in this position for the duration
of the test. DO NOT move the lever too far forward,
otherwise the parkbrake will not be fully operational.
Alternatively, disconnect the switch at the park brake.
3
Select 1st speed forward drive and open throttle fully.
Record the engine speed from the tachometer. Repeat
the test for 2nd and 3rd speed forward and record the
readings.
4
Repeat step
3
except this time select 1st, 2nd and 3rd
gear reverse drive respectively. Record the readings.
5
All recorded readings should be as specified at
Torque
Converter Stall
in Transmission Technical Data.
Key to Clutches
T
- Forward low ratio clutch pressure
U
- Forward high ratio clutch pressure
V
- Reverse high ratio clutch pressure
W
- Reverse low ratio clutch pressure
X
- 6 speed clutch pressure (6 speed gearbox only)
Y
- Mainshaft clutch pressure
Z
- Layshaft clutch pressure
Section F
9803/3280
Section F
65 - 1
Issue 1
Service Procedures
Stall Test Results - 6 Speed Powershift
Gear
Clutches engaged
Forward Rev/min
Reverse Rev/min
1st
X,Z
W,Z
2nd
T,Z
V,Z
3rd
U,Z
W,Y
Stall Test Results - 4 Speed Powershift
Gear
Clutches engaged
Forward Rev/min
Reverse Rev/min
1st
T,Z
W,Z
2nd
U,Z
V,Z
3rd
T,Y
W,Y
