Lull 6K Service Manual - Manual (Page 566)

Transmission
8-18 Service Manual — Models 644B, 6K, 844C, 8K, 1044C, 10K
A symptom of a failed park brake (or service 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).
Park Brake Pressure Switch Integrity Test
1. Apply the park brake.
2. Locate the park brake pressure switch and unplug both leads
connecting the pressure switch to the vehicle’s harness.
3. With a Digital Multi Meter (DMM) set to test continuity, connect the
DMM leads to the pins in one of the two pressure switch plugs. The
switch should be open. The DMM should display NO continuity.
4. Connect the leads of the DMM to the pins in the remaining pressure
switch plug. The switch should be open and the DMM should again
display NO continuity.
5. Start the engine, release the park brake, and shut the engine off.
6. With the DMM set to test continuity, connect the DMM leads to the pins
in one of the two pressure switch plugs. The switch should be closed.
The DMM should display continuity.
7. Connect the leads of the DMM to the pins in the remaining pressure
switch plug. The switch should be closed and the DMM should again
display continuity.
If one or both of the microswitches in the park brake pressure switch
consistently or intermittently fails to open when they both should be open,
remove and replace the pressure switch. Or, if both microswitches open
and one or both consistently or intermittently fails to close when both
should be closed, remove and replace the pressure switch (See “Park
Brake Pressure Switch” in Section 9).
Service Brake Pressure Switch
Description
The service brake pressure switch is a single pole, single throw, normally
open, 250 psi pressure switch connected between the service brake valve
and the wheel end brake assemblies. When the service brake is not
applied, there is no pressure at the service brake pressure switch and the
switch is open. The switch closes when the service brake is applied and
the pressure switch senses brake output pressure greater than 250 psi.
Machines w/ DW-2
Shifter For machines equipped with a DW-2 shifter, if this switch closes and the
transmission declutch switch (mounted in the dash panel) is in the “ON”
position, an electric signal is sent to the EST-19 microprocessor. This
signal enables the microprocessor to stop signals to the transmission
solenoids that engage forward/reverse and this declutches the
transmission.