Shifting Operation
Manual Shifting
In order to manually shift the transmission, the AUTO/MAN switch must be in the MAN position. Shifting the transmission is the main function of the power train electronic control module (ECM). The power train ECM interprets operator switch inputs. After the power train ECM interprets the operator switch inputs, the ECM shifts the transmission.
The power train ECM consists of the following switches and valves: upshift, downshift, direction, parking brake pressure, neutralizer switch and six transmission solenoid valves. The power train ECM processes the input information from the switches. Then, the ECM activates the appropriate transmission solenoid valves.
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| Illustration 1 | g00777055 |
(1) Direction control switch. (2) Upshift switch. (3) Downshift switch. | |
The shift switches for the transmission inform the power train ECM of requests that are made by the operator. The speeds that are requested by the operator follow: first gear, second, third gear and fourth gear. The directions that are requested by the operator follow: forward, reverse and neutral. The power train ECM activates the appropriate transmission solenoid valves when the operator makes a selection. Except for certain conditions, the power train ECM shifts the transmission according to these switch settings. Refer to table 1 for more information about shifting sequences.
| Normal Shifting Sequence | |||||
| Engaged Present Gear | If REVERSE Is Selected, Then The Transmission Shifts To Gear. | If NEUTRAL Is Selected Then The Transmission Shifts To Gear. | If FORWARD Is Selected Then The Transmission Shifts To Gear. | If UPSHIFT Is Selected Then The Transmission Shifts To Gear. | If DOWNSHIFT Is Selected Then The Transmission Shifts To Gear. |
| 4F | 4R | Neutral (4N) | No Change | No Change | 3F |
| 3F | 3R | Neutral (3N) | No Change | 4F | 2F |
| 2F | 2R | Neutral (2N) | No Change | 3F | 1F |
| 1F | 1R | Neutral (1N) | No Change | 2F | No Change |
| Neutral (1) (1N, 2N, 3N, 4N) |
Last (2) | No Change | Last (2) | Next (3) | Prior (3) |
| 1R | No Change | Neutral (1N) | 1F | 2R | No Change |
| 2R | No Change | Neutral (2N) | 2F | 3R | 1R |
| 3R | No Change | Neutral (3N) | 3F | 4R | 2R |
| 4R | No Change | Neutral (4N) | 4F | No Change | 3R |
| ( 1 ) | The number in the parentheses is shown on the gear readout. |
| ( 2 ) | A direction shift out of neutral will cause a speed shift to the last speed that was selected in either forward or reverse. |
| ( 3 ) | Speed shifts are allowed when neutral is selected. The gear readout will change the speed that is shown when neutral is selected and a speed shift is made. However, no solenoids are activated until the direction switch is moved to FORWARD or REVERSE. |
When the key start switch is turned from the OFF position to ON position, the power train ECM is activated. When the power train ECM is first activated, all the transmission solenoid valves are de-energized regardless of the position of the direction switch. The power train ECM then determines if the direction switch is in the NEUTRAL position. If NEUTRAL is NOT selected, then all the functions of the transmission are disabled. If the direction switch is in the NEUTRAL position, the power train ECM selects the present speed and the direction as neutral. If the direction switch is in the NEUTRAL position and AUTO/MAN switch is in the AUTO position, the power train ECM automatically selects the initial speed and direction as 2N. With the direction switch in the NEUTRAL position, the power train ECM allows the initial selected speed to be changed.
Note: The direction switch must be in the NEUTRAL position when the key start switch is turned to the START position. If the direction switch is not in the NEUTRAL position, the start relay will not be activated. Refer to System Operation, "Transmission Electronic Control Operation" for information about "Neutral Start Operation".
| Logic for the Transmission Modulating Solenoid Valve | |
| Machine Direction/Speed |
Transmission Modulating Valves Energized Direction and Speed |
| Neutral | None and 3 |
| Forward/First | 2 and 6 |
| Forward/Second | 2 and 5 |
| Forward/Third | 2 and 4 |
| Forward/Fourth | 2 and 3 |
| Reverse/First | 1 and 6 |
| Reverse/Second | 1 and 5 |
| Reverse/Third | 1 and 4 |
| Reverse/Fourth | 1 and 4 |
The transmission modulating solenoid valves that are located on the transmission, direct pilot oil to the ends of the control spool. The control spool will shift allowing pressure oil to the corresponding clutches. The power train ECM activates the transmission modulating valves. The ECM receives input from the following switches: direction switch, upshift switch and downshift switch. In order for the machine to move, two transmission solenoid valves must be activated. When the transmission is in neutral, no solenoid valves are activated.
Neutral Start Operation
The neutral start feature requires the direction switch to be in the NEUTRAL position, before the engine will crank. The operator controls this feature by placing the direction switch in the neutral position and turning the key start switch to the START position. This feature allows the engine to start only when the transmission is in the NEUTRAL position. When this feature is in operation, the power train ECM activates the start relay. The start relay allows the starting motor to turn.
Parking Brake Operation
The parking brake function prevents the operator from operating the machine while the parking brake is engaged. Driving through the parking brake causes accelerated wear to the friction components of the parking brake.
When the parking brake control is disengaged, the transmission will shift normally. When the parking brake control is engaged, the transmission will not shift out of neutral to first speed forward or first speed reverse. If the transmission is in first speed forward or in first speed reverse and the parking brake is moved to the engaged position, the transmission will shift into neutral. All of the clutch solenoid modulating valves are de-energized. If the transmission is in second speed forward or in third speed forward, the transmission will remain engaged.
The parking brake function activates a warning category 1 or a warning category 3 on the Caterpillar Monitoring System.
Warning category 1 is activated whenever the parking brake is engaged. The parking brake indicator will flash.
While the parking brake is engaged, warning category 3 will be activated. This will occur if the operator places the transmission direction control switch in the FORWARD position or the REVERSE position. The parking brake indicator will flash and the action lamp will flash. The action alarm will sound.
When the parking brake is engaged and the transmission is in first speed, the power train ECM shifts the transmission to neutral. The power train ECM also sends the parking brake status to the Caterpillar Monitoring System via the CAT Data Link. When the parking brake is engaged, the alert indicator for the parking brake flashes on the Caterpillar Monitoring System. If the operator selects the FORWARD position or the REVERSE position and the parking brake is engaged, the Caterpillar Monitoring System initiates a Warning Category 3. A Warning Category 3 causes the parking brake indicator and the action lamp to flash. The action alarm will also sound.
Reference: For more information on the Caterpillar Monitoring System, refer to the Service Manual module Systems Operation, "Caterpillar Monitoring System" for the machine that is being serviced.
Driving Through the Parking Brake
The power train ECM will allow the operator to drive through the parking brake. The machine should be moved only for a short distance.
In order to drive through the parking brake, the operator must select first speed forward or first speed reverse. The operator must then move the transmission direction control switch to the NEUTRAL position. The operator must then move the transmission direction control switch to the previous direction that was selected.
Backup Alarm Operation
The backup alarm function alerts surrounding personnel that the machine is backing up. The backup alarm is an output of the power train electronic control module (ECM). The power train ECM activates the backup alarm relay when the transmission direction control lever (if equipped) or the transmission direction control switch (if equipped) is in the REVERSE position. The backup alarm relay then activates the backup alarm. The backup alarm receives a +battery signal from the power train ECM when the backup alarm is activated.
Ride Control Function ( 980G) Only
Earlier Ride Control
The earlier ride control used a stem valve to control the ride of the machine. The stem valve is located on the right side of the inner portion of the loader frame.
Ride control is an optional feature that is determined by the options code plug. Ride control is enabled when the operator places the ride control switch in the ON or AUTO positions. In the ON position, the ride control is activated at all times and the power train ECM continuously energizes the ride control solenoid. In the AUTO position, the ride control function is dependent on the machine ground speed. When the ground speed increases above approximately 6 mph, ride control is activated. When the ground speed decreases below approximately 5.5 mph, ride control is deactivated. As ride control is activated and deactivated the ride control solenoid is energized and de-energized.
Later Ride Control
In the later ride control, the stem valve is replaced with a three-way solenoid valve and a pressure balance valve. The three-way solenoid valve and the pressure balance valve are located on the right side of the inner portion of the loader frame.
The three-way solenoid valve is energized when the following conditions exist:
- The key start switch is in the ON position.
- The ride control is in the OFF position.
- The ride control is in the AUTO position and the machine speed is below 6 mph.
This opens one end of the pressure balance valve to tank drain. The other end of the pressure balance valve always senses the head end pressure of the lift cylinder. This normally shifts the spool of the pressure balance valve. This will open the accumulator to the implement pump supply line. When an implement pump pressure is created by moving an implement, oil goes into the accumulator through a check valve. Then, the accumulator is charged with high pressure oil from the implement pump while the ride control is OFF.
When the ride control is ON, the three-way solenoid valve is turned off. This sends accumulator pressure to one end of the pressure balance spool. The other end of the pressure balance valve is sensing the pressure of the lift cylinder. The spool shifts in order to maintain the pressure of the accumulator at approximately 689 kPa (100 psi) higher than the pressure at the head end of the lift cylinder. After the pressure has been balanced for 5 seconds, the solenoid for the ride control diverter valve is energized. This opens the head end of the lift cylinder to the accumulator and the rod end of the lift cylinder to tank.
The ride control is immediately turned OFF in the following situation:
- The machine is operated with the ride control in the ON position.
- The operator tilts the implement forward in order to dump the load.
The ride control is turned OFF in order to prevent the lift arms from being pulled down by the tilt cylinder.
When the key start switch is turned to the OFF position, the solenoid for the ride control diverter valve is de-energized. Also, the three-way solenoid valve is de-energized. This opens the accumulator pressure to the pressure balance valve. Now, the system is a mode of pressure balanced. If the lift arms are in a raised position, oil is held in the accumulator at a pressure of approximately 689 kPa (100 psi) above the pressure in the head end of the lift cylinder. All the hydraulic oil in the accumulator should be drained to the tank under the following conditions:
- The work tool is placed on the ground.
- The pressure in the lift cylinder drops below 2482 kPa (360 psi).
- The accumulator nitrogen charge is at least 3172 kPa (460 psi).
Transmission Neutralizer
The transmission neutralizer neutralizes the transmission when the operator depresses the left brake pedal. To neutralize the transmission, the power train ECM deactivates the modulating solenoid valve for direction. The modulating solenoid valve for speed remains energized.
Note: The gear/direction readout on the monitor does not change when the transmission is neutralized. The monitor continues to show the speed and direction that will be engaged when the left brake pedal is released.
Override for the Transmission Neutralizer
The neutralizer override switch disables the transmission neutralizer control. The operator turns this feature on and off with the transmission neutralizer override switch. When the override switch is activated, pressing the left brake pedal does not cause the transmission to neutralize., Instead, the service brakes are applied.