28.
g. With the switch activated in the “RAISE” position and the motor start
solenoid is activated, check for voltage at the motor terminal. If voltage is
present and the motor is not running, replace the motor.
2. Problem – Liftgate will not raise to bed with a load and the pump motor running
Causes – a. Low hydraulic fluid
b. Overload condition
c. Improperly adjusted or defective main relief valve
d. Lift cylinder is bypassing, liftgate is drifting down
e. Broken hydraulic line
f. Clogged or disconnected suction line
g. Defective pump
Corrections - a. Make sure the reservoir has the proper amount of fluid. Remove the
breather cap and check the fluid line through the fill hole. The hydraulic
fluid should be within 1/2” of the top of the reservoir with the liftgate in the
lowered position. Fill with Dexron III automatic transmission fluid.
b. The power unit on the M is equipped with a lifting relief valve to prevent
overloading of the liftgate. See relief settings in “maintenance guide”
section of this manual.
c. See section “c” above for relief valve setting. Plumb a pressure gauge
into the high pressure circuit of the liftgate. Remove all loads from the
liftgate’s platform. Engage the “RAISE” switch until the liftgate is fully
raised. keep the “RAISE” switch engaged until the pump bypasses
through the relief valve and note the pressure on the gauge at this time. If
the rated relief pressure is not present during relief, adjust the high
pressure relief valve setting as necessary. If the relief pressure is not
attainable the relief valve must be cleaned and/or replaced or the pump is
defective. See part “g” below.
d. If the liftgate will not raise with a load on the platform but empty is raising
slowly or only partially, the cylinder may be bypassing. To check for a
bypassing cylinder do the following. Lower the gate to the ground to
relieve all pressure from the cylinder. Disconnect the cylinder from the
liftarm. Press the “RAISE” switch until the cylinder is fully retracted.
Disconnect the return line from the power unit and put the end of the line
in a container to catch any oil which comes out during this test. Press the
“RAISE” switch for 15 to 20 seconds and watch for a steady stream of
fluid coming out of the return line into the container. If no steady stream of
oil is present connect the hose to the butt end of the cylinder after
removing the return line and fitting. Re-attach the return line and fitting to
the rod end port. Put the loose end of the return line in a container to
catch any oil, which comes out during this test. Press the “RAISE” switch
until the cylinder is fully extended. Press the “RAISE” switch for 15 to 20
seconds and watch for a steady stream of fluid coming out of one of the
disconnected hose ends into the container. Replace or rebuild any
cylinder with fluid coming out of the return line, as this indicates fluid is
bypassing the piston seals on the cylinder. Reconnect rebuilt or replaced
cylinder and hoses as before.
e. Broken or punctured hydraulic lines and fittings must be replaced with
care to avoid injury from high pressure oil streams.
