777F Off-Highway Truck: Position Sensor (Hoist Control), Position Switch (Truck Body) & Oil Filter (Torque Converter Lockup Clutch)

Location of the hoist control position sensor
(1) Hoist control(2) Position sensor for the hoist control

Position sensor (2) is located on the right side of the operator's seat, and attached to hoist control (1). Position sensor (2) is a Pulse Width Modulation position sensor. Position sensor (2) sends duty cycle signals to the Chassis Electronic Control Module (Chassis ECM).

Note: Position sensor (2) does not need to be manually calibrated or adjusted. The machine performs an auto-calibration on the hoist control position sensor.

When the hoist control (1) is used, the position sensor (2) sends an electrical signal to the Chassis Electronic Control Module (Chassis ECM). The Chassis ECM uses this signal to energize the appropriate hoist proportioning solenoid on the hoist control valve. These hoist proportioning solenoids allow the spool in the hoist control valve to move. This will cause oil to be sent to the hoist cylinders in order to move the dump body.

The signal from the position sensor (2) is also used to neutralize the transmission. The Chassis ECM will allow only a forward speed position or the NEUTRAL position when position sensor (2) is in the RAISE position. The Chassis ECM will not allow a shift to the REVERSE position until the position sensor (2) has been moved from the RAISE position and the transmission shift lever is in the NEUTRAL position.

Note: If the machine is in REVERSE and position sensor (2) is in the RAISE position the Chassis ECM will shift the transmission to NEUTRAL. The machine will remain in NEUTRAL until hoist control (1) is moved into the HOLD or the FLOAT position and the transmission control has been cycled through NEUTRAL.

Position Switch (Truck Body)

(1) Magnet assembly(2) Body up or down switch

The body up or down switch (2) is located on a bracket on the rear frame. The magnet assembly (1) is connected to the dump body. When the dump body is raised, the body up or down switch (2) sends a signal to the Chassis Electronic Control Module (ECM). The signal indicates that the dump body is in the UP position. When the dump body is lowered, the magnet assembly (1) will pass in front of the body up or down switch (2) and a signal will be sent to the Chassis (ECM). This signal indicates that the dump body is DOWN. The adjustment of the body up or down switch (2) is very important. Refer to the Hydraulic System Testing and Adjusting, "Electronic Control (Body Down or Up Switch) - Adjust" for the proper adjustment procedure.

The body up or down switch (2) will limit the top gear that is being used while the dump body is in the UP position. The Chassis (ECM) comes from the factory with the top gear value that is set to FIRST gear. The transmission will not shift past FIRST gear until the dump body is down. The top gear value is programmable by utilizing the Electronic Technician (ET). The top gear value can be changed to SECOND gear, THIRD gear, or FOURTH gear.

The signal from the body up or down switch (2) is also used to control the SNUB position of the hoist control valve. The Chassis (ECM) will signal the hoist proportioning solenoids to move the hoist control valve to the SNUB position when the dump body that is being lowered nears the frame. The speed in FLOAT is reduced in the SNUB position in order to prevent the dump body from contacting the frame too hard.

The signal from the body up or down switch (2) is used to provide warnings to the operator when the truck is moving with the dump body in the UP position.

Oil Filter (Torque Converter Lockup Clutch)

(1) Inlet
(2) Outlet
(3) Oil sampling valve
(4) Pressure test port
(5) Bypass switch(6) Oil filter for the torque converter lockup clutch

The oil filter for the torque converter lockup clutch (6) is located on the left side of the frame assembly behind the front wheel.

The supply section of the gear pump for torque converter lockup sends the oil to the oil filter for the torque converter lockup clutch (6) .

Oil flows through inlet passage (1). The oil fills the space between the inside of the housing and the element. During normal operation, the oil flows through the element and out outlet passage (2) to the modulating valve for the torque converter lockup clutch and the pilot system for the hoist control. A relief valve for the pilot control pressure limits the maximum pressure of this supply oil. During normal operation, the element stops any debris that is in the oil.

If the element becomes full of debris, the restriction to the flow of oil cause a pressure increase inside the housing. The pressurized oil activates bypass switch (5) and an alarm is registered in the cab.

The oil then flows past the open bypass valve and to the modulating valve for the torque converter lockup clutch and the pilot system for the hoist control valve. When the oil does not flow through the element, the debris in the oil will cause damage to other components in the lockup clutch for the torque converter and the pilot system for the hoist control valve.

Use correct maintenance in order to make sure that the element does not become full of debris. If the element is full of debris, the flow of clean oil to the lockup clutch for the torque converter and the pilot system for the hoist control valve is stopped.

MARYGAR