Lull 6K Service Manual - Manual (Page 567)

Transmission
Service Manual — Models 644B, 6K, 844C, 8K, 1044C, 10K 8-19
Machines w/ DW-3
Shifter For machines equipped with a DW-3 shifter, a closed pressure switch
completes a circuit that sends an electric signal to the transmission
declutch relay. The relay energizes and stops power to the DW-3 shifter.
This prevents the shifter from sending the signals to the transmission
solenoids that engage forward/reverse and this declutches the
transmission.
When this switch senses pressure greater than 250 psi, it must close and
remain closed as long as the pressure stays above 250 psi. When the
pressure drops below 250 psi, the switch must open.
A symptom of a failed service brake (or park brake) pressure switch is a
transmission that will not go into forward or reverse (loss of forward and
reverse clutch packs). If this happens, check the pressure switch integrity
(see below).
Service Brake Pressure Switch Integrity Test
1. Install a 0–600 psi test gauge test gauge in the test port marked
“BRAKES” located beneath the operator’s compartment. Pressure
should read 0 psi.
2. Locate the service brake pressure switch and unplug the pressure
switch from the vehicle’s harness.
3. Using a DMM set to test continuity, connect the DMM leads to the pins
in the plug of the pressure switch. The switch should be open. The
DMM should display NO continuity.
4. Slowly depress the brake pedal while watching the pressure gauge
and the DMM display. As the pressure at the gauge rises and
approaches approximately 250 psi, the display on the DMM should
indicate continuity. The switch should close.
5. Slowly release the brake pedal while watching the pressure gauge and
the DMM display. As the pressure at the gauge falls below
approximately 250 psi, the display on the DMM should indicate NO
continuity. The switch should be open.
If the service brake pressure switch fails to close or if the service brake
pressure switch intermittently fails to close or closes and intermittently fails
to open, remove and replace the pressure switch (See “Service Brake
Pressure Switch Replacement” in Section 9).