4 hours ago
Core Symptoms and Operator Observations
A technician working with two nearly identical dozers—a Case 750K and a New Holland D75—encountered a puzzling issue: both machines exhibited extremely slow travel in forward and reverse. Initially, they moved at normal speed, but within seconds, travel speed dropped dramatically. Hydraulic pressures tested within spec, and filters were recently replaced, ruling out basic mechanical faults.
The technician monitored pump and motor current via diagnostic software. At gear engagement, motor current spiked to 40–50 amps and the machine pulled strongly. However, as speed dropped, motor current fell to zero and pump current dropped to 8–12 amps, fluctuating by gear. Left and right steering remained functional, though sluggish.
Terminology Notes
Both throttle and brake sensors failed to complete their full voltage sweep during calibration. When set to a released voltage of 4V, the pedals only reached 2.5V when fully depressed. This limited range prevented proper calibration and likely disrupted control logic.
The travel speed indicator on the dashboard behaved erratically. Sometimes it responded correctly, other times it lagged, jumped, or failed to move. However, the diagnostic laptop showed consistent and accurate readings from the up/down speed buttons. This discrepancy suggested a mismatch between actual speed and what the dashboard displayed—possibly affecting how the control system modulated travel.
The brake pedal sensor showed a range of 2.5V to 4V, but pressing the pedal had no effect on machine speed. The diagnostic software reported 85% brake when the pedal was fully raised and 30% when fully depressed, indicating the sensor was functioning but not influencing travel logic.
Throttle and Decel Pedal Issues
Throttle control was also compromised. Despite adjustments to the cable and linkage, full range of motion couldn’t be achieved. The throttle potentiometer remained out of spec, and the decel pedal felt unusually loose. An adjustment bolt was present, but its function was unclear, and documentation offered little guidance.
The diagnostic software showed a consistent gap between “set engine speed” and actual RPM—typically 300–400 RPM lower than expected. This mismatch could affect travel speed modulation, especially if the system relies on engine RPM to calculate torque availability.
Recommendations and Troubleshooting Strategy
Slow travel in Case 750K and NH D75 dozers can stem from a complex interplay of sensor calibration, electrical feedback, and control logic. While hydraulic systems may be healthy, electronic miscommunication between pedals, dashboard, and control modules can cripple performance. A methodical approach—starting with sensor range verification and wiring inspection—can restore full travel speed and ensure reliable operation.
A technician working with two nearly identical dozers—a Case 750K and a New Holland D75—encountered a puzzling issue: both machines exhibited extremely slow travel in forward and reverse. Initially, they moved at normal speed, but within seconds, travel speed dropped dramatically. Hydraulic pressures tested within spec, and filters were recently replaced, ruling out basic mechanical faults.
The technician monitored pump and motor current via diagnostic software. At gear engagement, motor current spiked to 40–50 amps and the machine pulled strongly. However, as speed dropped, motor current fell to zero and pump current dropped to 8–12 amps, fluctuating by gear. Left and right steering remained functional, though sluggish.
Terminology Notes
- Potentiometer Sweep: The full voltage range a sensor must travel through for accurate calibration.
- Motor Current: Electrical current drawn by the drive motor, indicating torque demand.
- Pump Current: Electrical current drawn by the hydraulic pump, reflecting fluid flow and pressure.
- Travel Speed Indicator: Dashboard gauge showing machine speed, often linked to sensor feedback and control logic.
Both throttle and brake sensors failed to complete their full voltage sweep during calibration. When set to a released voltage of 4V, the pedals only reached 2.5V when fully depressed. This limited range prevented proper calibration and likely disrupted control logic.
The travel speed indicator on the dashboard behaved erratically. Sometimes it responded correctly, other times it lagged, jumped, or failed to move. However, the diagnostic laptop showed consistent and accurate readings from the up/down speed buttons. This discrepancy suggested a mismatch between actual speed and what the dashboard displayed—possibly affecting how the control system modulated travel.
The brake pedal sensor showed a range of 2.5V to 4V, but pressing the pedal had no effect on machine speed. The diagnostic software reported 85% brake when the pedal was fully raised and 30% when fully depressed, indicating the sensor was functioning but not influencing travel logic.
Throttle and Decel Pedal Issues
Throttle control was also compromised. Despite adjustments to the cable and linkage, full range of motion couldn’t be achieved. The throttle potentiometer remained out of spec, and the decel pedal felt unusually loose. An adjustment bolt was present, but its function was unclear, and documentation offered little guidance.
The diagnostic software showed a consistent gap between “set engine speed” and actual RPM—typically 300–400 RPM lower than expected. This mismatch could affect travel speed modulation, especially if the system relies on engine RPM to calculate torque availability.
Recommendations and Troubleshooting Strategy
- Replace or Reposition Potentiometers: Ensure full sweep range is achievable. If mechanical limits prevent full travel, consider repositioning or replacing the sensors.
- Inspect Wiring and Connectors: Erratic dashboard readings may stem from poor connections or signal interference.
- Calibrate Brake and Throttle Sensors with Full Travel: Use mechanical adjustments to achieve full voltage range before software calibration.
- Test Decel Pedal Linkage and Spring Tension: A floppy pedal may fail to return properly, disrupting sensor readings.
- Compare Engine RPM and Set Speed Values: Investigate whether throttle control logic is misinterpreting RPM data due to sensor lag or calibration errors.
Slow travel in Case 750K and NH D75 dozers can stem from a complex interplay of sensor calibration, electrical feedback, and control logic. While hydraulic systems may be healthy, electronic miscommunication between pedals, dashboard, and control modules can cripple performance. A methodical approach—starting with sensor range verification and wiring inspection—can restore full travel speed and ensure reliable operation.
