66 - 6
Powershift Gearbox
Pressure and Flow Testing, cont’d
Converter Relief (Safety) Valve Pressure
The purpose of the torque converter relief valve is to protect
the torque converter from excessive oil pressure. Excessive
oil pressure can be generated when the transmission oil
temperature is below 50°C and/or the engine is run at over
2000 rev/min. In this event the relief valve opens and returns
oil directly to the transmission sump, bypassing the torque
converter, cooler and clutch lubrication circuits, protecting
against damage due to excessive pressure. For this reason
it is essential that the transmission oil is above 50°C and
the engine is run between idle and 1000 rev/min when
testing the relief valve.
1
Connect a 0-20 bar (0-300 lbf/in
2
) pressure gauge to
test point
B
.
2
Fit a load valve
P
into the converter out line.
!
CAUTION
Make sure the load valve is in the OPEN position, (the
adjusting knob screwed fully OUT), before starting the
following pressure test. Failure to do this could damage
the pump.
HYD 4-4/1
DO NOT
allow the pressure to exceed 8.3 bar (120 lbf/in
2
) or
damage to the converter seals will be caused.
3
Start the engine and run at 1000 rev/min. With the
transmission in neutral, slowly screw down the load
valve
P
whilst observing the gauge reading which
should rise to the
Converter Relief (Safety) Valve
setting as specified in Technical Data.
Note that the gauge pressure will fall once the valve has
opened. This is normal relief valve operation and does not
indicate a fault. If necessary reset the load valve
P
and
perform the test again, watching the pressure gauge
carefully.
4
If the converter relief valve opens at a pressure higher
than specified then the valve is faulty. A low opening
pressure indicates a leaking pump to casing seal or a
faulty converter relief valve.
5
Stop engine, remove test gauges and load valve. Refit
hoses to original position.
Converter Out Pressure/Oil Cooler Flow Rate
Note that the converter out pressure and oil cooler flow rate
are affected by the torque converter relief valve operation.
Before carrying out tests check the operation of the relief
valve (see
Converter Relief (Safety) Valve Pressure
.
1
Stop engine, connect a 0-20 bar (0-300 lbf/in
2
) pressure
gauge and flowmeter into the converter out line as
shown at
C
and
K
respectively.
2
Run the engine at 1000 rev/min with transmission in
neutral. The pressure gauge indicates the
Converter
Out Pressure
and the flowmeter indicates the
Oil
Cooler Flow Rate
, both readings should be as
specified in
Technical Data
. A high pressure together
with low flow could be caused by a blocked oil cooler
or internal leakage.
3
Repeat step
2
, with engine running at 2000 rev/min
note gauge readings which should be as shown in
Technical Data
.
4
Stop engine, remove test gauges and refit hoses to
original position.
Lubrication Pressure
Note that the lubrication pressure is affected by the torque
converter relief valve operation. Before carrying out tests
check the operation of the relief valve (see
Converter Relief
(Safety) Valve Pressure
.
1
Stop engine, connect a suitable pressure gauge into
the return line from the oil cooler to the transmission as
shown at
J
.
2
Start the engine and run at 1000 rev/min. With the
transmission in neutral the pressure gauge will indicate
the
Lubrication Pressure
which should be as specified
in
Technical Data
.
3
Repeat step
2
and note gauge readings with engine
running at 2000 rev/min. If the pressure is high the oil
cooler may be blocked, (see
Converter Out
Pressure/Oil Cooler Flow Rate
).
4
Stop engine and remove pressure gauge.
Section F
Transmission
9803/3280
Section F
66 - 6
Issue 1
Service Procedures
